References for “The Asian Monsoon” book – Chapter 6

"Proceedings of the International Conference on Monsoon Variability and Prediction: International Centre for Theoretical Physics, Trieste, Italy, 9-13 May 1994." (1994). Geneva, Switzerland, World Meteorological Organization 822.

Food production and water resources in many tropical and subtropical countries depend fundamentally on the strength of the annual monsoon. The ability to understand and predict variations in seasonal monsoonal circulations is of paramount importance to the large agrarian populations in these countries. In recent years, there have been major advances in predicting and simulating monsoons on a wide range of timescales using general circulation models, together with an increasing understanding of the atmospheric response to sea surface temperature anomalies. The International Conference on Monsoon Variability and Prediction held at the International Centre for Theoretical Physics, Trieste, Italy, 9-13 May 1994, provided a unique opportunity to discuss and review our understanding of monsoons, and our ability to predict monsoons using both empirical and dynamical modelling techniques. Over 130 papers were presented and the two volumes contain their extended abstracts. The contents are as follows: P. Webster, The monsoon: structure, properties and role in interannual variability; T. Yasunari, K. Ueno, T. Tomita, Role of tropical/extra-tropical interactions of the monsoon/atmosphere-ocean system (MAOS) in the tropics; S. Gadgil, S. Sridhar, Prediction of subseasonal variation of summer monsoon rainfall over the Indian region; M. Yanai, C. Li, Interannual variability of the Asian summer monsoon and its relationship with ENSO, Eurasian snow cover and heating; M. A. Bell, P. J. Lamb, Temporal variations in the rainfall characteristics of disturbance lines over sub-Saharan West Africa: 1951-90; M. A. El-Shahawy, A. M. Lasheen, African drought in relation to location and intensity of Hadley-circulation sectors; T. Tadesse, Summer monsoon seasonal rainfall of Ethiopia in ENSO episodic years; Y. Opoku-Ankomah, Towards prediction of monsoonal rainfall variability in Ghana; O. O. Jegede, Some aspects of the West African monsoon circulation as dedeuced from a geostationary satellite; J.E. Guilou-Via, Ondes atmospheriques de periode 6-8 jours a Dakar, ete 1984; W. S. Goma, Diagnosis of seasonal rainfall in comparison to monsoon variation; J. Citeau, M. Carn, S. Fongang, P. Sagna, Relationships between Western Africa ITCZ and St-Helena anticyclone suggested by a watch of METEOSAT-WV channel; L. A. Ogallo, Interannual variability of the East African monsoon wind systems and their impacts on East African climate; K.-M. Lau, S. Yang, The influence of the Asian monsoon on the predicability of the tropical coupled ocean-atmososphere system; B. Wang, T. Murakami, Summer monsoon in the eastern North Pacific; A. Kapala, K. Born, H. Flohn, Monsoon anomaly or an El Nino event at the equatorial Indian Ocean? Catastropic rains 1961/62 in East Africa and their teleconnections; D. R. Sikka, D. K. Paul, Monsoon variability over the Asia-Pacific region in relation to ENSO events; A. M. Choudhury, Bangladesh floods, cyclones and ENSO; R. N. Keshavamurty, Interannual and intraseasonal variability of monsoon; H. N. Srivastava, K. C. Sinha Ray, R. K. Mukhopadhyay, Intra-seasonal oscillations in cloud, rainfall, circulation, mixing ratio and radio-refractive index during southwest monsoon season over India; A. M. Grimm, P. L. Silva Dia, Some thoughts on teleconnections and the Indian monsoon; J. Corte-Real, X. Wang, Low-frequency oscillations and associated wave motions over Eurasia; Y. Xiang, C. Bao, J. Ding, El Nino event and monsoon rainfall, flooding in the Yangtze-Huaihe rivers; P.-S. Lu, Evolution of Asian summer monsoon and the slowly varying disturbances; R. P. Encarnacion, Simulation of cloudiness and rainfall during the cold surge of the northeast monsoon; I. I. Mokhov, Diagnostics of Indian monsoon interseasonal evolution and its relation with general evolution of cloudiness and precipitation fields over Eurasia by method of amplitude-phase characteristics; T. Nitta, Diurnal variations of convective activities in southeast Asia and tropical western p

"Proceedings of the international scientific conference on the Tropical Ocean Global Atmosphere (TOGA) programme, 2-7 April 1995, Melbourne, Australia." (1995). Geneva, Switzerland, World Meteorological Organization 911.

(Abstract continued) - role of air-sea coupling in the annual cycle in the tropical Pacific, D.-H. Wu; On the seasonality of the predictability of ENSO, B. N. Goswami,K. Rajendran and D. Sengupta; On the western Pacific warm pool during 1986-1989 simulated with an OGCM, C. Maes, J.-P. Boulanger, P. Delecluse and C. Levy; One year of variational assimilation in the tropical Atlantic, E. Greiner, S. Arnault and A. Morliere; Predictability of the tropical atmosphere, the tropical oceans and TOGA, J. Shukla; Seasonal mean wintertime atmospheric variabilities with and without SST anomalies, M. Ting and P. Heinselman; Simulated connection between the 1982-83 ENSO and the 1984 Atlantic warm event, J. Servain, P. Delecluse, C. Levy, J.-F. Royer; Simulation of the 1982-1983 El Nino using an OGCM, P. Dandin and P. Delecluse; Single column model experiments in the TOGA COARE region, S. F. Iacobellis and R. C. J. Somerville; Structure and momentum fluxes of several TOGA COARE convective systems, D.P. Jorgensen, B. F. Smull, S. Lewis and M. A. LeMone; Systematic errors in the NMC coupled ocean atmosphere model, K. C. Mo, M. Ji and A. Leetmaa; The mechanism of mixed layer intraseasonal variations in the `warm pool' area, Q. Liu, J. Sun and S. Jiang; The role of the annual cycle in the predictability of the coupled ocean-atmosphere system: experiments with complex intermediate coupled systems, P. J. Webster; The role of wind and radiative forcing of interannual sea surface temperature anomalies in the tropical Atlantic, L. Lo and A. J. Busalacchi; The roles of SST anomalies and latent heat release in the formation of atmospheric teleconnection patterns and intraseasonal oscillation modes, J. S. Frederiksen and C. S. Frederiksen; Variability in ENSO predictive skill, D. L. T. Anderson; Symposium 5: Predictions of low frequency variability, and their application: An improved initialization procedure for El Nino forecasting, D. Chen, A. Busalacchi, S. E. Zebiak and M. A. Cane; Annual cycle and interannual variability of SST during 1985-1990, S. K. Dash, P. K. Mohanty and B. Jha; Atmospheric parameterizations in coupled air-sea models used for forecasts of ENSO, K. Miyakoda, J. Sirutis, A. Rosati, T. C. Gordon, R. Gudgel, W. F. Stern, J. Anderson and A. Navarra; China monsoonal rainfall and western Pacific Ocean temperatures, I. Simmonds and B. Yan; Climate predictions with a coupled GCM, B. P. Kirtman, B. Huang, J. Shukla, Z. Zhu and E. K. Schneider; Coupled model forecasting analysis of ENSO at BMRC, R. Kleeman, N. R. Smith and A. M. Moore; Coupling between extratropical and tropical interannual anomalies during ENSO cycle, V. V. Efimov, A. V. Prusov and M. V. Shokurov; ENSO, equatorial Pacific SST, NAO and the sea ice extent in the Northern Hemisphere, S. S. Dugam; Fisheries applications of the TOGA Monitoring Program in the Atlantic and Indian oceans: predictability of interannual oscillations in spiny lobster catches driven by ocean climatic changes, M. Vianna; Forecasting intraseasonal variability: An operational approach, S. Cleland and P. Bate; Low frequency intraseasonal oscillations over India and their potential in prediction, S. V. Singh, R. H. Kripalani and S. R. Inamdar; NIMBUS-7 SMMR snow mass and Indian monsoon rainfall, R. H. Kripalani; Prediction of the equatorial Pacific SST indices using a projection pursuit regression analysis, J.-E. Shi; Preliminary study on southern oceanic oscillation, S. Xie, C. Bao and C. Hao; Short term climate prediction: TOGA to GOALS, E. S. Sarachik; Southern Oscillation-precipitation relationships: opportunities for improved predictions, C. F. Ropelewski, M. S. Halpert and V. E. Kousky; Systems for operational climate forecasts, A. Leetmaa and M. Ji; The 1991-95 extended warm Pacific event: Southern Hemisphere effects and predictability, W. J. Wright, I. N. Smith and R. J. Allan; The accuracy of the Victorian component of the Australian Bureau of Meteorology's Seasonal Outlook Service, H. Stern

Adams, D. K. and A. C. Comrie (1997). "The North American monsoon." Bulletin of the American Meteorological Society, Boston, MA 78(10): 2197-2213.

The North American monsoon is an important feature of the atmospheric circulation over the continent, with a research literature that dates back almost 100 years. The authors review the wide range of past and current research dealing with the meteorological and climatological aspects of the North American monsoon, highlighting historical development and major research themes. The domain of the North American monsoon is large, extending over much of the western United States from its region of greatest influence in northwestern Mexico. Regarding the debate over moisture source regions and water vapor advection into southwestern North America, there is general agreement that the bulk of monsoon moisture is advected at low levels from the eastern tropical Pacific Ocean and the Gulf of California, while the Gulf of Mexico may contribute some upper-level moisture (although mixing occurs over the Sierra Madre Occidental). Surges of low-level moisture from the Gulf of California are a significant part of intraseasonal monsoon variability, and they are associated with the configuration of upper-level midlatitude troughs and tropical easterly waves at the synoptic scale, as well as the presence of low-level jets, a thermal low, and associated dynamics (including the important effects of local topography) at the mesoscale. Seasonally, the gulf surges and the latitudinal position of the midtropospheric subtropical ridge over southwestern North America appear to be responsible for much spatial and temporal variability in precipitation. Interannual variability of the North American monsoon system is high, but it is not strongly linked to El Nino or other common sources of interannual circulation variability. Recent mesoscale field measurements gathered during the South-West Area Monsoon Project have highlighted the complex nature of the monsoon-related severe storm environment and associated difficulties in modeling and forecasting.

Ahlquist, J., V. Mehta, et al. (1990). "Intraseasonal monsoon fluctuations seen through 25 years of Indian radiosonde observations." Mausam, New Delhi, India 41(2): 273-278.

Radiosonde records for 12 major Indian cities have been checked and analyzed for intraseasonal activity in the monsoon. After forming time series with two observations per day, removing bad values, and filling data gaps with linear interpolation, the time series have been plotted with and without filtering and have been subjected to spectral analysis to reveal the nature of intraseasonal fluctuations and their interannual variability. Spectra were estimated from the time series using the maximum entropy method (MEM), which fits an autoregressive (AR) model to the time series. MEM spectra based on tenth order AR models show that most of the variance in monsoon weather comes from intraseasonal activity with periods longer than 10 days, but do not show separate peaks at 10-20 and/or 30-50 day time scales for the majority of summers.

Anderson, D. L. T. (1981). "Equatorial and monsoon dynamics." World Climate Programme Meeting on Time Series of Ocean Measurements, Tokyo, May.

Various aspects of ocean dynamics thought to be relevant to the formation of SST (sea surface temperature) anomalies are examined, and a variety of time series or data sets available for confirmation are summarized. The author examines the simplest model of equatorial flow, obtained by assuming no pressure gradients and by applying the u momentum equation (u sub(t) = X) at the Equator, and estimates the time for which this equation is applicable. The simple dynamics of the Yoshida jet and thermocline tilting are analyzed primarily on the basis of the work of Wyrtki. Evidence for equatorial waves is reviewed. Interannual processes associated with wave propagation in the Pacific Ocean, as represented by the El Nino phenomenon, and in the Atlantic Ocean, as represented by remote forced upwelling and its interannual variation in the Gulf of Guinea, are discussed.

Angell, J. K., J. Korshover, et al. (1984). "Variation in United States cloudiness and sunshine, 1950-82." Journal of Climate and Applied Meteorology, Boston 23(5): 752-761.

The variation in cloudiness and percentage of possible sunshine for the contiguous U.S. and six regions thereof is examined, on the basis of data from 101 National Weather Service stations for the years 1950-1982. Over this 33-yr interval, linear regression analysis indicates a 3.7% increase in U.S. cloudiness significant at the 1% level, but a nonsignificant (at the 5% level) 0.9% decrease in sunshine. This difference in trend magnitude and significance may be related to an increase in cirrus, perhaps partly aircraft induced. Changes in the U.S. cloudiness during this interval have been greatest in autumn (7.0%) and least in spring (1.7%), and for year-average values, greatest in the southwest (4.7%) and south-central (4.4%) regions, and least in the north-central (2.5%) and northeast (2.8%) regions. There is a highly significant (at the 0.1% level) correlation of -0.92 between year-average U.S. cloudiness and sunshine, which shows that dust, smoke, and haze have not had a large effect on sunshine duration. There have also been no anomalous changes of sunshine duration relative to cloudiness after the Agung, Mt. St. Helens, and El Chichon eruptions. The positive correlations between cloudiness values (and sunshine values) for the most distant regions of the U.S. show that some of the interannual variations in these quantities are of large spatial extent. There has been an appreciable tendency (although not quite significant at the 5% level), particularly in the southwest and the north- and south-central regions, for cloudiness to be above average and sunshine below average in years of warm sea surface temperature (SST) in the equatorial eastern Pacific (El Nino). This tendency was pronounced during the unusually warm SST years of 1972 and 1982, when U.S. cloudiness was 4.0 and 4.7% above average, respectively, and sunshine 3.5 and 3.1% below average, respectively. There is no evidence for a consistent relationship between the quasi-biennial oscillation in the tropical stratosphere and U.S. cloudiness or sunshine. There has, however, been a significant tendency (at the 5% level) for U.S. cloudiness to be above average and sunshine below average in years when Indian summer or monsoon rainfall is below average, and vice versa, with respective correlations of -0.42 and 0.46. There is no evidence for a relation between Northern Hemisphere surface temperature and U.S. cloudiness or sunshine in the same year, but there is evidence for a relation with cloudiness and sunshine one year later.

Annamalai, H. and J. M. Slingo (2001). "Active/break cycles: diagnosis of the intraseasonal variability of the Asian Summer Monsoon." Climate Dynamics 18(1/2): 85-102.

In this study, various diagnostics have been applied to daily observed outgoing longwave radiation (OLR) and ECMWF ReAnalysis (ERA) products to provide a comprehensive description of the active/break cycles associated with the Asian Summer Monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability, 10-20 days and 30-60 days. Composite analysis of OLR based on filtered daily All-India rainfall (AIR) for the 40 day (30-60 days) intraseasonal mode indicates that during active phases, convection is significantly enhanced over the Indian continent, extending over the Bay of Bengal, Maritime continent and equatorial west Pacific, while convection is suppressed over the equatorial Indian Ocean and northwest tropical Pacific, resulting in a quadrapole' structure over the Asian monsoon domain. In response to this heating pattern, the large-scale Hadley (lateral) and the two east-west (transverse) tropical circulations are enhanced. There is also a significant impact on the extra-tropical circulation through excitation and propagation of Rossby waves. In contrast, the 15-day mode is more regional to the monsoon domain and has a prominent east-west orientation in convection. Only the local Hadley circulation over the monsoon region is modulated by this mode. The evolution of these two modes as revealed by POP (principal oscillation pattern) analysis, shows that the 40-day mode originates over the equatorial Indian Ocean. Once formed it has poleward propagation on either side of the equator, and eastward propagation into the equatorial west Pacific. From the equatorial west Pacific, northward propagation over the west Pacific and westward propagation into the Indian longitudes are prominent. The propagative features are complex and interactive and are responsible for the quadrapole' structure in convection seen from the composites. The interannual variability, assessed from the POP coefficient time series, indicates that the 40-day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic TCZ (tropical convergence zone). The POP analysis of the 15-day mode indicates that this event originates over the equatorial west Pacific, associated with westward propagating Rossby waves, amplifies over the northwest tropical Pacific and modulates both the continental and oceanic TCZs over Indian longitudes simultaneously. This mode is pronounced during the established phase of the monsoon. Due to the complexity in the propagational features of both the intraseasonal modes, it is concluded that understanding the subseasonal variability of one regional component of the Asian Summer Monsoon (ASM), requires understanding the entire ASM system.

Annamalai, H., J. M. Slingo, et al. (1999). "The mean evolution and variability of the Asian summer monsoon: comparison of ECMWF and NCEP-NCAR reanalyses." Monthly Weather Review, Boston, MA 127(6, Pt. 2): 1157-1186.

The behavior of the Asian summer monsoon is documented and compared using the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA) and the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) Reanalysis. In terms of seasonal mean climatologies the results suggest that, in several respects, the ERA is superior to the NCEP-NCAR Reanalysis. The overall better simulation of the precipitation and hence the diabatic heating field over the monsoon domain in ERA means that the analyzed circulation is probably nearer reality. In terms of interannual variability, inconsistencies in the definition of weak and strong monsoon years based on typical monsoon indices such as All-India Rainfall (AIR) anomalies and the large-scale wind shear based dynamical monsoon index (DMI) still exist. Two dominant modes of interannual variability have been identified that together explain nearly 50% of the variance. Individually, they have many features in common with the composite flow patterns associated with weak and strong monsoons, when defined in terms of regional AIR anomalies and the large-scale DMI. The reanalyses also show a common dominant mode of intraseasonal variability that describes the latitudinal displacement of the tropical convergence zone from its oceanic-to-continental regime and essentially captures the low-frequency active/break cycles of the monsoon. The relationship between interannual and intraseasonal variability has been investigated by considering the probability density function (PDF) of the principal component of the dominant intraseasonal mode. Based on the DMI, there is an indication that in years with a weaker monsoon circulation, the PDF is skewed toward negative values (i.e., break conditions). Similarly, the PDFs for El Nino and La Nina years suggest that El Nino predisposes the system to more break spells, although the sample size may limit the statistical significance of the results.

Arpe, K., L. Duemenil, et al. (1998). "Variability of the Indian monsoon in the ECHAM3 model: sensitivity to sea surface temperature, soil moisture, and the stratospheric quasi-biennial oscillation." Journal of Climate, Boston, MA 11(8): 1837-1858.

The variability of the monsoon is investigated using a set of 90-day forecasts [MONEG (Tropical Ocean Global Atmosphere Monsoon Numerical Experimentation Group) experiments] and a set of AMIP-type (Atmospheric Model Intercomparison Project) long-term simulations of the atmospheric circulation with the ECHAM3 model. The large-scale aspects of the summer monsoon circulation as represented by differences of dynamical quantities between the two extreme years 1987 and 1988 were reproduced well by the model in both kinds of experiments forced with observed sea surface temperature (SST). At the regional scale the difference of precipitation over India during summer 1987 and 1988 was well reproduced by the model in the 90-day forecasts using interannually varying SSTs; however, similarly good results were achieved in forecasts using climatological SSTs. The long-term simulations forced with interannually varying SST at the lower boundary of the atmosphere over a period of 14 years, on the other hand, only partly reproduce the observed differences of precipitation over India between 1987 and 1988. For the ensemble mean of five simulations averaged from June to September and for the whole of India an increase from 1987 to 1988 is simulated by the model as observed but with smaller values. The difference in observed precipitation between 1987 and 1988 is of opposite sign for May to that for September. The simulations and observations agree in the manifestation of this sense of opposing variability within a monsoon season for these two years and also for other years. The simulations and observations differ most during July. The paper concentrates on the question why the interannual variability in the long-term simulations on one hand and the 90-day forecasts and in the observations of precipitation on the other hand differ so strongly during the peak of the monsoon in July. Large-scale dynamics over India are mainly forced by the anomalies of Pacific SST. For the variability of precipitation over India other forcings than the Pacific SST are important as well. Due to enhanced evaporation, warmer SSTs over the northern Indian Ocean lead to increased precipitation over India. Changes in the SST there within the range of uncertainty (0.5 K) can lead to clear impacts. As a further boundary forcing, the impact of soil moisture is investigated. The use of realistic soil moisture differences between 1987 and 1988 in the MONEG forecasts resulted in improved skill of precipitation forecasts over India. Also the two individual AMIP simulations with realistic precipitation differences over India had more realistic soil moisture differences over east Asia in the beginning of the monsoon season between the two years than those experiments that failed to produce the correct precipitation differences. The years 1987 and 1988 were quite different with respect to the phase of the stratospheric quasi-biennial oscillation (QBO). As atmospheric circulation models cannot yet reproduce stratospheric QBOs realistically, their impact was tested by nudging observed QBOs into AMIP simulations for July 1987 and 1988. Seven out of eight experiments showed an impact toward a more realistic simulation of precipitation over India; however, during the west phase of the QBO (1987) impacts are very small. None of these forcings gave a dominant effect. If this finding is confirmed by further experimentation, improvements of practical long-range forecasts may be very difficult as two of these quantities are hardly known with the required accuracy (northern Indian Ocean SSTs and the Eurasian soil moisture) and because models are not yet able to simulate the stratospheric QBO realistically. This study confirms that El Nino has two direct effects: it reduces the precipitation over India and reduces the surface winds over the Arabian Sea. Due to the latter, the SST of the Arabian Sea can increase as there is less mixing and upwelling in the ocean. Here it is suggested that

Ashok, K., Z. Guan, et al. (2001). "Impact of the Indian Ocean Dipole on the Relationship between the Indian Monsoon Rainfall and ENSO." Geophysical Research Letters 28(23): 4499-4502.

The influence of the recently discovered Indian Ocean Dipole (IOD) on the interannual variability of the Indian summer monsoon rainfall (ISMR) has been investigated for the period 1958-1997. The IOD and the El Nino/Southern Oscillation (ENSO) have complementarily affected the ISMR during the last four decades. Whenever the ENSO-ISMR correlation is low (high), the IOD-ISMR correlation is high (low). The IOD plays an important role as a modulator of the Indian monsoon rainfall, and influences the correlation between the ISMR and ENSO. We have discovered that the ENSO-induced anomalous circulation over the Indian region is either countered or supported by the IOD-induced anomalous meridional circulation cell, depending upon the phase and amplitude of the two major tropical phenomena in the Indo-Pacific sector.

Ashrit, R., S. K. Mandke, et al. (1999). "Sensitivity of a GCM simulation of two contrasting Indian monsoons to SST anomaly distributions." Theoretical and Applied Climatology, Vienna, Austria 63(1-2): 57-64.

One of the major forcings for the interannual variability of the Asian Summer Monsoon is the Sea Surface Temperature (SST) distribution in the tropical Pacific Ocean. El Nino years are characterized by a negative Southern Oscillation Index (SOI) and a decreased monsoon rainfall over India leading to drought conditions. On the other hand, La Nina years are characterized by a positive SOI and generally good monsoon conditions over India. The monsoon ENSO relation is not a consistent one. The monsoons of 1991 and 1994 are good examples. The spring SOI was the same (-1.3) during both years. However, the All India Summer Monsoon Rainfall (AISMR) was 91.4% of normal in 1991 and 110% in 1994. Though the SOI was same during the spring of both years, the spatial distribution of SSTs was different. In the present study, the impacts of different SST distributions in the tropical Pacific Ocean, on the monsoons of 1991 and 1994 have been examined, to assess the UKMO-unified model's sensitivity to SST. It is observed that the simulated monsoon was much stronger in 1994 than in 1991, in terms of precipitation and circulation. The wind and the Outgoing Long-wave Radiation (OLR) simulated by the model are compared with NCEP/NCAR reanalyses data, while precipitation is compared with Xie-Arkin merged rainfall data.

Bansod, S. D., K. D. Prasad, et al. (2000). "Stratospheric zonal wind and temperature in relation to summer monsoon rainfall over India." Theoretical and Applied Climatology, Vienna, Austria 67(3-4): 115-121.

The interannual variability of the Indian summer monsoon (June-September) rainfall is examined in relation to the stratospheric zonal wind and temperature fluctuations at three stations, widely spaced apart. The data analyzed are for Balboa, Ascension and Singapore, equatorial stations using recent period (1964-1994) data, at each of the 10, 30 and 50 hPa levels. The 10 hPa zonal wind for Balboa and Ascension during January and the 30 hPa zonal wind for Balboa during April are found to be positively correlated with the subsequent Indian summer monsoon rainfall, whereas the temperature at 10 hPa for Ascension during May is negatively correlated with Indian summer monsoon rainfall. The relationship with stratospheric temperatures appears to be the best, and is found to be stable over the period of analysis. Stratospheric temperature is also significantly correlated with the summer monsoon rainfall over a large and coherent region, in the north-west of India. Thus, the 10hPa temperature for Ascension in May appears to be useful for forecasting summer monsoon rainfall for not only the whole of India, but also for a smaller region lying to the north-west of India.

Barnett, T. P. (1984). "Interaction of the monsoon and Pacific trade wind system at interannual time scales, Pt. 3, Partial anatomy of the Southern Oscillation." Monthly Weather Review, Boston 112(12): 2388-2400.

Studies of surface wind fields, sea surface temperature (SST), precipitation, and sea level pressure in the tropical band extending plus or minus 30 degrees of the Equator from Africa to South America led to the following conclusions. The Southern Oscillation, El Nino, and climatic variations in the monsoon system are all part of one global-scale phenomenon. In the sea level pressure field, this phenomenon seems to have a strong propagating component that appears first in the northern Indian Ocean and moves eastward into the eastern Pacific. Similar propagation of information was found in the surface wind field and equatorial precipitation regimes. These same conditions were amply demonstrated during the 1982-1983 event, and it may be concluded that the evolution of that event bears many similarities to those in the historical record studies referred to in this paper. In the surface wind field of the equatorial waveguide, the large-scale signal appears to take the form of a forced Kelvin wave. The mechanism that drives this wave appears to be latent heat release associated with precipitation anomalies that are phase locked to, and propagate with, the surface wind anomalies. The long time scales associated with the atmospheric anomalies may be associated either with the slow interaction between the Walker and Hadley cells or with ocean-atmosphere coupling. Variations in the SST in the central equatorial Pacific appear to be due almost exclusively to advective processes and not to local air-sea heat exchange, a result in accord with that of other studies. All SST anomalies in the equatorial region seem to be closely related to earlier variations in the zonal wind over the maritime continent, such as perturbations in the Indonesian low which appear as the eastward propagating node of the Pacific Walker cell. It appears to be this feature of the wind field that eventually forces the observed ocean response. Extremely limited data show a remarkable coincidence between an empirically derived histogram of recurrence intervals between El Nino events derived from wind field considerations alone and similar histograms derived by Quinn et al. from completely different data sets. The former distribution function assumes that tropical climate variations can be characterized as frequency-modulated processes.

Barnett, T. P. (1984). "Interaction of the monsoon and Pacific trade wind system at interannual time scales, Pt. 2, Tropical band." Monthly Weather Review, Boston 112(12): 2380-2387.

The author concentrates on the tropical band within plus or minus 30 degrees of the Equator; an earlier study (Part 1) concentrated on the region plus or minus 10 degrees of the Equator. The results of this study show that the two wind systems are strongly coupled across the tropical latitudes at interannual time scales with coherent variations apparent in the surface wind field from Africa to South America. It appears that the equatorial regions are coupled most strongly to the Southern Hemisphere. The couplings and interaction between the two systems are dependent upon the phase of the annual cycle. The apparent temporal bimodality observed in Part 1 in the near-equatorial band is no longer seen when the full tropical band is analyzed. There is only a slight preference in the wind system for anomalous convergence over Indonesia. The eastward propagation of anomalous zonal wind in the equatoral region is still evident in this analysis. The results suggest that the atmosphere changes its state in a way that is only broadly related to changes in the sea surface temperature (SST) in the central Pacific. Thus, it appears that mechanisms other than those associated with the Pacific SST may be required to explain much of the variability described. It also appears that the climatic signal described is only part of an even larger mode of climatic variability.

Barnett, T. P. (1989). "Effect of Eurasian snow cover on regional and global climate variations." Journal of the Atmospheric Sciences, Boston 46(5): 661-685.

The sensitivity of the global climate system to interannual variability of the Eurasian snow cover has been investigated with numerical models. It was found that heavier than normal Eurasian snow cover in spring leads to a poor monsoon over Southeast Asia, verifying an idea 100 yr old. The poor monsoon was characterized by reduced rainfall over India and Burma, reduced wind stress over the Indian Ocean, lower than normal temperatures on the Asian land mass and in the overlying atmospheric column, reduced tropical jet, increased soil moisture, and other features associated with poor monsoons. Lighter than normal snow cover led to a good monsoon with atmospheric anomalies like those described above, but of opposite sign. Remote responses from the snow field perturbation include readjustment of the Northern Hemispheric mass field in midlatitude, an equatorially symmetric response of the tropical geopotential height and temperature field, and weak, but significant, perturbations in the surface wind stress and heat flux in the Tropical Pacific. The physics responsible for the regional response involves all elements of both the surface heat budget and heat budget of the full atmospheric column. In essence, the snow, soil, and atmospheric moisture all act to keep the land and overlying atmospheric column colder than normal during a heavy snow simulation, thus reducing the land-ocean temperature contrast needed to initiate the monsoon. The remote responses are driven by heating anomalies associated with both large-scale air-sea interactions and precipitation events. The model winds from the heavy snow experiment were used to drive an ocean model. The SST field in that model developed a weak El Nino in the equatorial Pacific. A coupled ocean-atmosphere model simulation perturbed only by anomalous Eurasian snow cover was also run, and it developed a much stronger El Nino in the Pacific. The coupled system clearly amplified the wind stress anomaly associated with the poor monsoon. These results show the important role of an evolving (not specified) sea surface temperature in numerical experiments and the real climate system. The general results also demonstrate the importance of land processes in global climate dynamics and their possible role as one of the factors that could trigger ENSO events.

Basu, B. K. (2001). "Simulation of the Summer Monsoon over India in the Ensemble of Seasonal Simulations from the ECMWF Reanalyzed Data." Journal of Climate 14(7): 1440-1449.

The ensemble of seasonal (120 days) simulations of the Northern Hemispheric summer for the reanalysis period of the European Centre for Medium-Range Weather Forecasts has been examined to assess the extent to which the characteristic features of the Indian summer monsoon can be reproduced in these simulations. The present simulations could reproduce a better distribution of the seasonal average precipitation over India in comparison with the earlier Atmospheric Model Intercomparison Project simulations. The Interannual variation in the seasonal total of the spatially averaged precipitation over India has predictability. The 10-day-average precipitation values did not show any impact of the El Nino or La Nina events or any periodicity in the amount of precipitation. The intraseasonal variability did not produce any distinct pattern for 10-day-average rainfall during the excess or deficient years. The simulated patterns over India correspond to the weak phase of summer monsoon with excess precipitation over the northern part of the country and adjoining China. The cloud cover is less over the central parts of India and near-ground maximum temperature is higher. A simulated motion field reproduces the typical features of the Indian summer monsoon including the low-frequency seasonal migration of the Tibetan anticyclone at 200 hPa.

Basu, B. K. (2001). "Simulation of the summer monsoon over India in the ensemble of seasonal simulations from the ECMWF reanalyzed data." Journal of Climate, Boston, MA 14(7): 1440-1449.

The ensemble of seasonal (120 days) simulations of the Northern Hemispheric summer for the reanalysis period of the European Centre for Medium-Range Weather Forecasts has been examined to assess the extent to which the characteristic features of the Indian summer monsoon can be reproduced in these simulations. The present simulations could reproduce a better distribution of the seasonal average precipitation over India in comparison with the earlier Atmospheric Model Intercomparison Project simulations. The interannual variation in the seasonal total of the spatially averaged precipitation over India has predictability. The 10-day-average precipitation values did not show any impact of the El Nino or La Nina events or any periodicity in the amount of precipitation. The intraseasonal variability did not produce any distinct pattern for 10-day-average rainfall during the excess or deficient years. The simulated patterns over India correspond to the weak phase of summer monsoon with excess precipitation over the northeastern part of the country and adjoining China. The cloud cover is less over the central parts of India and near-ground maximum temperature is higher. A simulated motion field reproduces the typical features of the Indian summer monsoon including the low-frequency seasonal migration of the Tibetan anticyclone at 200 hPa.

Basu, S., S. D. Meyers, et al. (2000). "Annual and interannual sea level variations in the Indian Ocean from TOPEX/POSEIDON observations and ocean model simulations." Journal of Geophysical Research, Washington, DC 105(C1): 975-994.

Sea level variations relative to a 4-year mean in the Indian Ocean north of 10 degrees S are examined during 1993-1996 using both a numerical reduced gravity model with realistic coastline geometry and wind stress and sea level measurements from the TOPEX/POSEIDON altimeters. The annual signal is found to be composed of propagating as well as nonpropagating features. The propagation speeds in the model and altimetry generally agree to within 25% or less. Complex empirical orthogonal function (CEOF) decomposition yields a separation between the annual and semiannual cycles (46 and 30% of the respective variance for the model, and 40 and 26% for the altimetric measurements, respectively). The propagation of these signals across the ocean basin is indicated by the spatial phase functions. Both temporal phase functions are steady for the annual cycle, though the amplitudes are modulated in time. The results for the semi-annual cycles are similar, but the temporal phase functions are disrupted for similar to 12 months starting in 1994. This may be due to an unusually strong monsoon during that time. The correlation between model sea level variation and those measured by altimetry is highly variable in both space and time. Low-frequency filtering of the sea level anomalies, obtained by summing the two largest CEOF modes (the annual and semiannual cycles), improves the correlation. The filtered anomalies correlate in time as high as 0.9 in the western Arabian Sea and as high as 0.7 south of the equator and in the eastern Bay of Bengal. There are pockets of poor correlation (as low as -0.4) in the eastern Arabian Sea, central Bay of Bengal, and central equatorial region. These areas tend to contain recurring Rossby wave interactions as represented by the 1.5-layer model. Each area is associated with a ``phase nexus'' (analogous to an amphidromic point in tidal theory) or a strong gradient of the model spatial phase functions. The spatial correlation between the filtered anomalies is typically 0.6 over much of the observation period but contains unexplained declines as low as 0.2 during a few months in both 1995 and in 1996.

Becker, B. D., J. M. Slingo, et al. (2001). "Seasonal predictability of the Indian Summer Monsoon: What role do land surface conditions play?" Mausam 52(1): 175-190.

Anomalous springtime snow amounts over Eurasia may provide long term memory to the climate system by affecting the land surface energy and moisture budgets. In turn the anomalous land surface conditions introduced by snow anomalies may influence monsoon variability. In this paper, results from a programme of seasonal forecast ensembles are used to address, specifically, the influence of western Eurasian land surface conditions on the variability and hence predictability of the Indian summer monsoon. The factors that are important for establishing spring time land surface conditions over western Eurasia, particularly snow amounts are also investigated. The results have shown that high snow amounts over western Eurasia are linked to La Nina, suggesting that the El-Nino/Southern Oscillation (ENSO) has an influence on the wintertime climate of Eurasia. The signature of these snow depth anomalies is carried through to the summer in terms of changes in soil wetness and surface temperatures. An ensemble of summer integrations with climatological sea surface temperature (SST) has been used to investigate the impact of these anomalous land surface conditions on monsoon variability. The results have shown that the monsoon circulation is substantially weakened in association with above normal snow amounts over western Eurasia, whilst All India Rainfall is slightly increased. Results from a parallel ensemble with observed SSTs show an opposite response in All India Rainfall, suggesting that the forcing by SST anomalies is potentially dominating the monsoon's interannual variability. The results have demonstrated that land surface conditions can have a significant impact on the large scale monsoon circulation and to a lesser extent on Indian Summer Monsoon rainfall, although the mechanisms involved have yet to be identified. It is suggested that interactions between the mid-latitude circulation and the monsoon may hold the key to understanding the link between Eurasian land surface conditions and monsoon variability. If that is the case then predictability of this relationship is likely to be limited, due to the high level of internal variability of the mid-latitude circulation.

Behera, S. K., P. S. Salvekar, et al. (2000). "Simulation of interannual SST variability in the tropical Indian Ocean." Journal of Climate, Boston, MA 13(19): 3487-3499.

A 2.5-layer thermodynamic ocean model is used to investigate interannual variability in sea surface temperature (SST) of the tropical Indian Ocean. Simulated SST agrees well with the data. Model and observed SSTs exhibit large seasonal and interannual variability in the western and southeastern tropical Indian Ocean. Three processes, namely, latent heat flux, radiative flux, and entrainment, play major roles in the evolution of model SST anomalies. Interannual heat flux is found to have greater influence on the SST anomalies in most parts of the model domain. On the other hand, influence of interannual wind is only pronounced near the coasts in the Arabian Sea during the Asian summer monsoon season and a region in the central part of the southern tropical Indian Ocean (STIO) during boreal winter. Besides the El Nino-Southern Oscillation related basinwide warming, empirical orthogonal function analysis shows a dipole structure in both model and observed SST anomalies in the STIO. The eastern pole is anomalously cold with a peak occurring 4-8 months prior to the negative peak of the Southern Oscillation. A similar dipole structure in the latent heat flux anomalies explains the dipole in the SST anomalies.

Beltrando, G. and P. Camberlin (1993). "Interannual variability of rainfall in the eastern Horn of Africa and indicators of atmospheric circulation." International Journal of Climatology, New York, NY 13(5): 533-546.

Relationships between rainfall variations in the eastern Horn Of Africa, the Southern Oscillation, and the Indian Ocean temperature and pressure surface fields are studied for the period 1932-83. Rainfall data consist of stations and regional indices calculated for three selected areas experiencing quite different rainfall patterns. The results indicate significant negative correlations between northern autumn rains in Somalia and the Southern Oscillation during the same season. These rains are also negatively correlated with pressure in the western Indian Ocean, and positively correlated in the eastern Indian Ocean. The reverse pattern is shown with sea-surface temperature. This agrees very well with the observations made in Kenya as far as the short rains of October-November are concerned. Central Ethiopia summer rains, in contrast, indicate significant positive correlations with the Southern Oscillation, at zero and 3 months lag. El Nino years often correspond to drought years in this region. Evidence of an inverse relationship between the amount of rainfall in Ethiopia during summer (especially during September) and both the pressure and sea temperature over the Indian Ocean is also given. Correlations with the Arabian Sea are particularly strong. However, teleconnections between summer rains in northern Ethiopia (Eritrea) and the ENSO or the Indian Ocean fields are much weaker. These results suggest that, although summer rains over Ethiopia are said to be related to the monsoon air flow from the Congo Basin and the Atlantic Ocean, there also exist quite strong connections with the surface conditions prevailing in the Indian and Pacific Oceans.

Bess, T., G. Smith, et al. (1992). "Annual and interannual variations of Earth-emitted radiation based on a 10-year data set." Journal of Geophysical Research, Washington, DC 97(D12): 12825-12835.

Earth-emitted radiation varies in space and time due to variations of atmospheric and surface temperature, clouds, and water vapor. The method of empirical orthogonal functions (EOFs) has been applied to a 10-year data set of outgoing longwave radiation to study this variability. Spherical harmonic functions are used as a basis set for producing equal area map results. The following findings are noted. The first EOF accounts for 66% of the variance. After that, each EOF accounts for only a small variance, forming a slowly converging series. The first two EOFs describe mainly the annual cycle. The third EOF is primarily the semiannual cycle, although many other EOFs also contain significant semiannual parts. These results reaffirm earlier studies based on a shorter data set. In addition, a much stronger spring/fall mode was found in the central equatorial Pacific Ocean for the second EOF than had been found earlier. This difference is attributed to the use of broadband radiometer data which were available for the present study. The earlier study used data from a window-channel instrument which is not as sensitive to water vapor variations. The fourth EOF describes much of the 1976-1977 and 1982-1983 ENSO phenomena. There is typically a gap in the spectrum between a semiannual peak and the annual cycle for all but the first EOF. A semiannual dipole straddles the Asian-Australian monsoon track.

Bethoux, J. P. (1987). "Climatic variability of transports between the Red Sea and the Indian Ocean." Oceanologica Acta, Paris 10(3): 285-291.

Study of the heat budget of the Red Sea, a concentration basin semienclosed by the sills and straits of Bab al Mandab, permits evaluation of the annual evaporation, which, with other elements of the water and salt budgets, permits, in turn, a determination of mean transports. The seasonal cycle of the water budget is calculated from the seasonal cycle of evaporation (evaluated from mean annual values and from meteorological data) and from monthly sea level data. During winter, the outflow of dense Red Sea water is strengthened by the occurrence of light-density water in the Gulf of Aden, advected by the Northeast monsoon. Inversely, in summer, the concentration basin dynamics are disturbed by the inflow of subsurface water from the Gulf of Aden. Determination of the heat content of the surface layer (0-150 m) permits evaluation of the extension, volume, and spatial-temporal behavior of this subsurface water. Linked to the summer monsoon in the Indian Ocean, which provokes an upwelling and an increase in subsurface water density in the Gulf of Aden, this water inflows to 18 degrees N lat. then outflows back from the Red Sea when the summer monsoon decays. The seasonal cycle of transports through the Strait of Bab al Mandab shows the monsoon driving force effects superimposed upon the concentration basin transports, and the probable effect of the monsoon interannual variability. The zonal differentiation that occurs at similar to 18 degrees N as a result of topography and climate is, thus, strengthened by hydrology and water masses. Dynamic or geochemical studies must take into consideration this zonal differentiation, which is influenced by the movement of Aden subsurface water and has biological implications.

Bhalme, H. N. (1996). "Some Aspects on CLIPS." Second Session of the CCI Working Group.

Monsoons occur in different parts of the world and they are of great importance to several countries, especially in south-east Asia and Africa on account of the associated seasonal rainfall. Although the monsoon is a regular annual event, it exhibits large interannual variability, which sometimes produces natural calamities like drought and flood. These conditions actually have a direct bearing on the economy of most of the countries in the region which are predominantly agriculture depend with inadequate irrigation facilities and water management. Those countries which are dependent on agriculture none has a rainfall as uncertain as that of India. The occurrence of drought during the Indian monsoon (June-September) is one of the worst natural event creating misery and hardship for millions living under its influence. In view of the great importance of monsoon to India there have been many studies to understand its interannual variability and eventually to forecast its behaviour better. The emphasis of this paper is on interannual variability of the Indian monsoon and its relationship with regional and global factors.

Bhalme, H. N., A. B. Sikder, et al. (1990). "Relationships between planetary-scale waves, Indian monsoon rainfall and ENSO." Mausam, New Delhi, India 41(2): 279-284.

The relationships between the El Nino phenomenon and the planetary-scale waves, and the interannual variations in the Indian monsoon (June-September) rainfall have been analysed to investigate as to how SST in the equatorial eastern Pacific associated with the El Nino can produce reduced monsoon rainfall over India which are at widely separated parts of the globe. In terms of the observed relationships, a plausible mechanism for linking El Nino with the reduced Indian monsoon rainfall is discussed. The relationships noted suggest that large warm SST anomalies associated with El Nino induce eastward shift in the planetary waves which in turn reduce the Indian monsoon rainfall.

Bhalme, H. N., A. B. Sikder, et al. (1991). "Interannual monsoon variability." WMO Tropical Meteorology Research Programme.

Large-scale features associated with the interannual variability of Indian monsoon (June-September) rainfall are reviewed. The Indian monsoon rainfall does not show significant long-term increase /decrease but it shows large variability on an interannual scale. Although the actual causes of interannual variability of monsoon are not adequately understood, many processes have been hypothesized as possible causes. The external causes involve changes in amount of solar radiation reaching the outer limit of the Earth's atmosphere while the internal causes are based on changes with Earth-atmosphere system. The 11-yr sunspot cycle in Indian monsoon rainfall has been noticed in some studies but not in others. Recent studies indicate more convincing response to the 22-yr cycle (Hale or Double sunspot cycle). It has been observed that the areal extent of flood (i.e. excessive rainfall) over India during the summer monsoon fluctuates with a period of about 22-yr showing strong coherence with double sunspot cycle. Large-scale flood events over India have not occurred consistently in alternate sunspot cycle. However large-scale drought events have no preference. The correlation between Indian monsoon rainfall and preceding winter Eurasian snow cover and NH surface air temperature are so small, though physically real, that they are of insufficient value for useful forecasting of the Indian monsoon. The Indian monsoon rainfall show highest and highly significant correlation with one season later rather than earlier SOI and SST in the equatorial eastern Pacific. It tends to be followed rather than preceded by variations elsewhere. It is now established that a major ENSO episode shifts eastward the convective regimes of the tropical belt. This is the dominant factor for deficient rains over southeast Asian regions. The ENSO phenomenon is the most notable and dominant factor for interannual variability of the Indian monsoon.

Bhaskaran, B., J. F. B. Mitchell, et al. (1995). "Climatic response to the Indian subcontinent to doubled CO sub(2) concentrations." International Journal of Climatology, Chichester, UK 15(8): 873-892.

Results from the United Kingdom Meteorological Office (UKMO) coupled climate model have been analysed over the Indian subcontinent in order to validate the model's performance and to assess the changes in climate and its variability in a simulation with a 1 percent increase per year in CO sub(2) (compound). The model produces a reasonable simulation of present-day climate over the Indian subcontinent. At the time of CO sub(2) doubling, the model simulates temperature increases of the order of 1 K to 4 K over the Indian subcontinent during winter and monsoon seasons. The model-simulated monsoon circulation shifts by 10 degrees latitude towards the north and intensifies by approximately 10 percent in the warmer atmosphere. The interannual variability of monsoon onset dates and intraseasonal variability of monsoon rainfall are not significantly different when the CO sub(2) concentration doubles. However, the model simulates increased interannual variability of the monsoon rainfall and a greater number of heavy rainfall days during the monsoon.

Biswas, N. C. (1989). "Interannual variability of the advance of Indian summer monsoon and associated rainfall." Mausam, New Delhi 40(3): 329-332.

The onset of the summer monsoon over Kerala and its subsequent advance over the whole country are spectacular. In this paper, the onset of southwest monsoon over Kerala and Gangetic West Bengal and its north and westward march over the country; seasonal rainfall associated with early, normal, and delayed advance; and features related to rapid or slow process of advance have been studied in detail. Harmonic analysis of the area weighted monsoon rainfall over the country as a whole and areas of normal or excess and deficient rainfall for a period of 35 yr have also been computed. Triennial, seven, and 17-yr cycles of the rainfall variation during the season have been observed.

Borgaonkar, H. P. and G. B. Pant (2001). "Long-term climate variability over monsoon Asia as revealed by some proxy sources." Mausam 52(1): 9-22.

Studies on climate variability over the region of monsoon Asia mostly during the Quaternary, based on various sources of proxy data have been reviewed. Increasing interest to understand the processes of monsoon system over the Asian region as well as the availability of data from variety of reliable proxy sources such as, ocean sediments, ice cores and historical documents have encouraged the palaeoclimatic studies in this region. Inferences drawn from the multiproxy sources indicate good association of glacial and inter-glacial phases with over all monsoon flow. Warm and wet periods are generally characterized by strong summer monsoon, where as, weak monsoonal activities were observed during cold and dry periods. All India monsoon rainfall since early 17th century based on dendroclimatic reconstructions shows trend-less nature with large interannual variability as seen in the instrumental record of recent century. Historical evidences over this region are a potential source of information on contemporary climate change.

Brankovic, C. and T. N. Palmer (1997). "Atmospheric seasonal predictability and estimates of ensemble size." Monthly Weather Review, Boston, MA 125(5): 859-874.

Results from a set of nine-member ensemble seasonal integrations with a T63L19 version of the European Centre for Medium-Range Weather Forecasts (ECMWF) model are presented. The integrations are made using observed specified sea surface temperature (SST) from the 5-year period 1986-90, which included both warm and cold El Nino-Southern Oscillation (ENSO) events. The distributions of ensemble skill scores and internal ensemble consistency are studied. For years in which ENSO was strong, the model generally exhibits a relative high skill and high consistency in the Tropics. In the northern extratropics, the highest skill and consistency are found for the northern Pacific-North American region in winter, whereas for the northern Atlantic-European region the spring season appears to be both skillful and consistent. For years in which ENSO was weak, the distributions of ensemble skill and consistency are relatively broad and no clear distinction between Tropics and extratropics can be made. Applying a t test to interannual fluctuations over various tropical and extratropical regions, estimates of a minimum useful ensemble size are made. Explicit calculations are done with ensemble size varying between three and nine members; estimates for larger sizes are made by extrapolating the t values. Based on an analysis of 2-m temperature and precipitation, the use of relatively large (approximately 20 members) ensembles for extratropical predictions is likely to be required; in the Tropics, smaller-sized ensembles may be adequate during years in which ENSO is strong, particularly for regions such as the Sahel. The role of the SST forcing in a seasonal timescale ensemble is to bias the probability distribution function (PDF) of atmospheric states. Such PDFs can, in addition, be a convenient way of condensing a vast amount of data usually obtained from ensemble predictions. Interannual variability in PDFs of monsoon rainfall and regional geopotential height probabilities is discussed.

Brankovic, C., T. N. Palmer, et al. (1991). "Seasonal simulations with ECMWF NWP model." Programme on Long Range Forecasting Research.

Some results from a set of integrations with the T42 version of the ECMWF NWP model over the northern summers of 1987 and 1988 and with specified SSTs are presented. The year 1987 was a severe drought over both India and the African Sahel; 1988 was an above-average monsoon year for India, with rains over the Sahel close to the climatological mean, and flooding in the Sudan. Also in the late spring and early summer of 1988, a large area of the North American continent experienced the worst drought during this century. During both years the El Nino-Southern Oscillation (ENSO) cycle shifted from the warm to the cold phase. The capacity of the model to simulate both global-scale and regional seasonal mean circulations and associated rainfalls was investigated by carrying out integrations 90 days in duration. The model included a significant revision to the bulk parameterization of sensible and latent heat flux which was to increase substantially the surface evaporation in regions of weak grid-box mean wind. The model was run without cumulus friction. On seasonal time scales, the ECMWF NWP model with observed SST simulated observed interannual variation in 1987 and 1988 in the global-scale velocity potential, and stream function fields. This variation is also seen in the regional tropical rainfall, in particular in monsoon regions. The experimental results indicate that the late spring and summer 1988 SST anomalies may have played an important role in establishing a strong ridge over the North American continent.

Breidenbach, J. (1990). "EOFs of pseudo-stress over the Indian Ocean (1977-85)." Bulletin of the American Meteorological Society, Boston, MA 71(10): 1448-1454.

The method of empirical orthogonal function (EOF) analysis is applied to pseudo-stress vectors over the Indian Ocean from 1977 to 1984. The EOF method is first reviewed, as it provides an easy method for comprehensive study of the climatology and variance of the pseudo-stress dataset. The results confirm that the monsoon flow is the dominant feature in the Indian Ocean, with strong southeasterly trades near the equator in summer and strong southwesterlies in the Arabian Sea, Bay of Bengal, and South China Sea. During the Northern Hemisphere winter, the pattern is weaker, with the wind switching to northeasterlies in these areas. Strong summer monsoons occurred in 1980, 1982, and 1984. Strong winter monsoons occurred in 1980, 1983, and 1984. An interesting pattern contributing to the decay and reversal of the monsoon flow is examined here. During the 1977-83 period, most of the interannual variability occurred in the Southern Hemisphere in the southeast trades. Strong southeast trades occurred in 1981 and 1982. Weaker periods of southeast trades were present from 1977 to 1979, with more northerly southeast trades in 1978 and 1979. Weak southeast trades occurred in 1983 but slowly changed to strong southeast trades by 1985.

Cadet, D. L. and B. C. Diehl (1984). "Interannual variability of surface fields over the Indian Ocean during recent decades." Monthly Weather Review, Boston 112(10): 1921-1935.

The interannual variability of surface meteorological fields over the Indian Ocean during the period 1954-1976 is studied by using 2 million ship reports obtained from different sources. Monthly mean fields of wind, pressure, air temperature, mixing ratio, cloud cover, and sea surface temperature (SST) on a grid mesh of 2 degrees have been determined by computing the monthly mean values of the data around each grid point. Because data coverage is poor over certain areas, an objective analysis based on the successive correction method was performed. Seasonal anomaly fields are presented for the Northern Hemisphere summers of 1956 and 1972, with the two summers having opposite extreme features. During 1956 (1972), the intensity of the trade winds in the Southern Hemisphere and the summer cross-equatorial flow were above (below) normal. Sea surface temperature was below (above) normal over the entire Indian Ocean in 1956 (1972). Time series of the anomalies over different key areas show that weaker than normal trade winds persisted during a period extending from 1968 to 1974. As a consequence, the summer cross-equatorial flow was reduced, mainly along the African coast, by similar to 20%. During the same period, SST and air temperatures were above normal (to 2 degrees C during the 1972 summer), presumably because of the decrease of evaporation and turbulent mixing of the surface layer by weaker winds. The fluctuations of the different surface parameter anomalies seem to be related to a similar variation of the activity of the summer monsoon: the end of the 1960s and the beginning of the 1970s correspond to dry monsoons. This is supported by fields of correlation coefficients between summer rainfall over India and different parameters over the Indian Ocean.

Campbell, G., T. G. F. Kittel, et al. (1995). "Low-frequency variability and CO sub(2) transient climate change. Part 2: EOF analysis of CO sub(2) and model-configuration sensitivity." Global and Planetary Change, Amsterdam, The Netherlands 10(1-4): 201-216.

We used empirical orthogonal function (EOF) analysis to examine the monthly variance structure of several general circulation model (GCM) simulations to look for possible systematic changes of variability, not only due to increased carbon-dioxide (CO sub(2) ) concentration in the atmosphere but also due to model configuration. We evaluated four simulations which were present-day and doubled CO sub(2) experiments with the same atmospheric GCM coupled to (1) a simple nondynamic mixed-layer ocean (termed ``mixed-layer model'') and (2) an ocean GCM (termed ``coupled model''). Model-generated variability, as represented by EOFs of 700-mb height, is similar in all cases for global analyses and is mainly characterized by an opposition of sign between mid- and high latitudes in both hemispheres. This overall pattern does not appreciably change with a doubling of CO sub(2) in the models. However, there are regional changes between 1 x CO sub(2) and 2 x CO sub(2) runs which are similar for the mixed-layer and coupled models. These changes include shifts of centers of variability in the Pacific and Atlantic sectors of the Northern Hemisphere that are similar to changes in persistent height anomalies or ``blocking'' noted in a previous study. Changes in model configuration give rise to more extensive changes in the overall pattern of variation, with variability in Northern and Southern Hemispheres more tightly linked in the coupled model than in the mixed-layer model. We also computed EOFs using only model data for the tropics (between 30 degrees N and 30 degrees S). In these EOFs, differences between the two model configurations in terms of geographic centers of variability and time series power spectra are greater than between 1 x CO sub(2) and 2 x CO sub(2) cases. This is because the coupled model simulates some aspects of the El Nino-Southern Oscillation (ENSO) while the mixed-layer version does not. Consequently, different model configuration has a stronger effect on simulated interannual variability globally than does altered CO sub(2) forcing. Because ENSO is not represented in the mixed-layer model, CO sub(2) -induced changes in variability are not credible in that model. For the coupled model, regional increases in variability, such as over the monsoon region of south Asia, are consistent with results from other analyses. We also evaluated CO sub(2) sensitivity of the coupled model's seasonal cycle of surface air temperatures using a harmonic analysis. Strongly different seasonal cycles appear in the high latitudes of the Northern Hemisphere in the coupled model under different CO sub(2) conditions, This phenomenon, noted in earlier studies with mixed-layer models, is apparently mostly due to snow and ice reductions with increased CO sub(2) that contribute to a smaller-amplitude annual harmonic and larger-amplitude half-year harmonic of surface air temperature. Similar reductions in amplitude of the annual harmonic at high northern latitudes are noted in observed surface air temperature data in a recent period compared to an earlier period in this century.

Campbell, W. H., J. B. Blechman, et al. (1983). "Long-period tidal forcing of Indian monsoon rainfall: an hypothesis." Journal of Climate and Applied Meteorology, Boston 22(2): 287-296.

This paper examines the nature of the periodic components observed in the interannual variability of June rainfall in northern India by using an eigenvector analysis of the spectra of the June rainfall record (1895-1975) and an eigenvector analysis of the precipitation data itself for stations in that region. The first eigenvectors of these analyses have similar spatial and spectral characteristics that indicate that in June the atmosphere in northern India responds strongly at two frequencies, 0.05 and 0.26 yr super(-) super(1) . These two frequencies match the two dominant frequencies in the spectrum of a time series (1895-1975) of the mean monthly solilunar tidal potential at the latitude of northern India. It is hypothesized that tidal effects modulate the advance of the monsoon front, producing some of the observed interannual variability. This hypothesis has been tested by using the tidal frequencies to predict June rainfall a year in advance. The success rate of these year-in-advance forecasts in northern India, on independent data, significantly exceeded that expected by chance or predicted by interannual persistence, suggesting that mechanical tidal forcing might be a useful additional long-range forecast tool.

Castro, C. L., T. B. McKee, et al. (2001). "The Relationship of the North American Monsoon to Tropical and North Pacific Sea Surface Temperatures as Revealed by Observational Analyses." Journal of Climate 14(24): 4449-4473.

The North American monsoon is a seasonal shift of upper- and low-level pressure and wind patterns that brings summertime moisture into the southwest United States and ends the late spring wet period in the Great Plains. The interannual variability of the North American monsoon is examined using the NCEP-NCAR reanalysis (1948-98). The diurnal and seasonal evolution of 500-mb geopotential height, integrated moisture flux, and integrated moisture flux convergence are constructed using a 5-day running mean for the months May through September. All of the years are used to calculate an average daily Z score that removes the diurnal, seasonal, and intraseasonal variability. The 30-day average Z score centered about the date is correlated with Pacific sea surface temperature anomaly (SSTA) indices associated with the El Nino-Southern Oscillation (ENSO) and the North Pacific oscillation (NPO). These indices are Nino-3, a North Pacific index, and a Pacific index that combines the previous two. Regional time-evolving precipitation indices for the Southwest and Great Plains, which consider the total number of wet or dry stations in a region, are also correlated with the SSTA indices. The use of nonnormally distributed point source precipitation data is avoided. Teleconnections are computed relative to the climatological evolution of the North American monsoon, rather than to calendar months, thus more accurately accounting for the climatological changes in the large-scale circulation. Tropical and North Pacific SSTs are related to the occurrence of the Pacific Transition and East Pacific teleconnection patterns, respectively, in June and July. A high (low) NPO phase and El Nino (La Nina) conditions favor a weaker (stronger) and southward (northward) displaced monsoon ridge. These teleconnection patterns affect the timing and large-scale distribution of monsoon moisture. In the Great Plains, the spring wet season is lengthened (shortened) and early summer rainfall and integrated moisture flux convergence are above (below) average. In the Southwest, monsoon onset is late (early) and early summer rainfall and integrated moisture flux convergence are below (above) average. Relationships with Pacific SSTA indices decay in the later part of the monsoon coincident with weakening of the jet stream across the Pacific and strengthening of the monsoon ridge over North America.

Chakraborty, B. and M. Lal (1994). "Monsoon climate and its change in a doubled CO sub(2) atmosphere as simulated by CSIRO9 model." TAO, Taiwan, PRC 5(4): 515-536.

In this paper, the author presents an assessment of the likely climate changes over the Indian subcontinent and the intraseasonal and interannual variability in summer monsoon rainfall as a consequence of increasing greenhouse gas concentrations in the atmosphere as inferred from CSIRO9 climate model simulations. The data obtained from the control and doubled CO sub(2) experiments with the model, each for 24-equilibrium years, are analyzed in this study. The model demonstrates a reasonable skill in simulating the present-day climate and its interannual variability over the Indian subcontinent. The total seasonal rainfall over India under the influence of southwest monsoon activity as inferred from the control run is in fair agreement with the observed climatology. A rise in area-averaged surface temperature of 2.98 degrees during the monsoon season over India (for land points only) is projected by the model in a doubled CO sub(2) atmosphere. Though no significant change in the monsoon onset date is found, an intensification of monsoonal rainfall is simulated by the model in a warmer atmosphere. The seasonal changes in the other hydrological parameters (evaporation and soil moisture) simulated by the model for the doubled CO sub(2) atmosphere are also discussed.

Chan, S. C. and J. L. Evans (2002). "Comparison of the Structure of the ITCZ in the West Pacific during the Boreal Summers of 1989-93 Using AMIP Simulations and ECMWF Reanalysis." Journal of Climate 15(24): 3549-3568.

The dynamic structure and interannual variability of the ITCZ in the western North Pacific and east Asia during the boreal summers of 1989-93 are investigated. European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses are used to characterize the dynamical structure of the ITCZ. The ITCZ structure in the National Center for Atmospheric Research (NCAR) Community Climate Model 3 (CCM3.6) and the National Aeronautics and Space Administration (NASA) Goddard Institute of Space Studies (GISS) SI2000 GCM is also explored. The ITCZ axis can be partitioned into three sections in the western North Pacific and east Asia: the continental monsoon trough (CMT) in India, the Bay of Bengal, and Indo-China; the oceanic monsoon trough (OMT) in the Pacific warm pool; and the trade wind trough (TWT) in the central Pacific. The confluence point (CP) is defined as an area where the broad cyclonic flow in OMT changes to the easterly trades of the TWT. East of the CP, both GCMs simulate a weaker easterly trade wind regime with a broader ITCZ due to the dislocation of the Pacific high. To the west of the CP, both GCMs simulate a weaker cross-equatorial flow and OMT. Both models show skill in simulating the interannual variability of the location of the CP; however, for the peak ENSO warm phase years (1992-93), the spread among ensemble members of the CP longitude is comparable to the shift of ensemble mean CP location relative to 1989. That is, the internal variability of each GCM is on the same order as the simulated interannual variability in this region.

Chang, C. P. and T. Li (2000). "A theory for the tropical tropospheric biennial oscillation." Journal of the Atmospheric Sciences, Boston, MA 57(14): 2209-2224.

The key questions of how the tropospheric biennial oscillation (TBO) maintains the same phase from northern summer in South Asia to southern summer in Australia, and how the reversed phase can last through three locally inactive seasons to the next monsoon, are studied by a simple tropical atmosphere-ocean-land model. The model has five boxes representing the South Asian and Australian monsoon regions and the equatorial Indian and western and eastern Pacific Oceans. The five regions interact with each other through the SST-monsoon, evaporation-wind, monsoon-Walker circulation, and wind stress-ocean thermocline feedbacks. A biennial oscillation emerges in a reasonable parameter regime, with model SST and wind variations resembling many aspects of the observed TBO. Warm SST anomalies (SSTA) in July in the equatorial Indian Ocean cause an increase of surface moisture convergence into South Asia, leading to a stronger monsoon. The monsoon heating on one hand induces a westerly wind anomaly in the Indian Ocean, and on the other hand intensifies a planetary-scale east-west circulation leading to anomalous easterlies over the western and central Pacific. The westerly anomaly over the Indian Ocean decreases the local SST, primarily by evaporation-wind feedback. The easterly anomaly in the central Pacific causes a deepening of the ocean thermocline in the western Pacific therefore increasing the subsurface and surface temperatures. In addition, a modest easterly anomaly in the western Pacific opposes the seasonal mean westerlies so evaporation is reduced. These effects overwhelm those of the cold zonal advection and anomalous upwelling. The net result is warm SSTA persisting in the western Pacific through northern fall, leading to a stronger Australian monsoon. Meanwhile, the warming in the western Pacific also induces a stronger local Walker cell and thus a surface westerly anomaly over the Indian Ocean. This westerly anomaly helps the cold SSTA to persist through the succeeding seasons, leading to a weaker Asian monsoon in the following summer. During northern winter the westerly anomaly associated with the stronger Australian monsoon, through anomalous ocean downwelling and reduction of evaporation (when the seasonal mean wind is easterly), reinvigorates the warm SSTA in the western Pacific, which has been weakened by the slow cold advection from the eastern Pacific. This further intensifies the eastern Walker cell and helps to keep the eastern Pacific cold. The authors' theory indicates that the TBO is an inherent result of the interactions between northern summer and winter monsoon and the tropical Indian and Pacific Oceans. Thus, it is an important component of the tropical ocean-atmosphere interaction system, separate from the El Nino-Southern Oscillation. While the eastern Pacific plays only a passive role in this mechanism, the western Pacific-Maritime Continent region is crucially important. It serves as a bridge in space and time, both in connecting the convection anomaly from the northern summer to the northern winter monsoon and in channeling the feedback of the northern winter monsoon to the Indian Ocean.

Chang, C. P., Y. Zhang, et al. (2000). "Interannual and interdecadal variations of the East Asian summer monsoon and tropical Pacific SSTs. Part I: Roles of the subtropical ridge." Journal of Climate, Boston, MA 13(24): 4310-4325.

The interannual relationship between the East Asian summer monsoon and the tropical Pacific SSTs is studied using rainfall data in the Yangtze River Valley and the NCEP reanalysis for 1951-96. The datasets are also partitioned into two periods, 1951-77 and 1978-96, to study the interdecadal variations of this relationship. A wet summer monsoon is preceded by a warm equatorial eastern Pacific in the previous winter and followed by a cold equatorial eastern Pacific in the following fall. This relationship involves primarily the rainfall during the pre-Mei-yu/Mei-yu season (May-June) but not the post-Mei-yu season (July-August). In a wet monsoon year, the western North Pacific subtropical ridge is stronger as a result of positive feedback that involves the anomalous Hadley and Walker circulations, an atmospheric Rossby wave response to the western Pacific complementary cooling, and the evaporation-wind feedback. This ridge extends farther to the west from the previous winter to the following fall, resulting in an 850-hPa anomalous anticyclone near the southeast coast of China. This anticyclone 1) blocks the pre-Mei-yu and Mei-yu fronts from moving southward thereby extending the time that the fronts produce stationary rainfall; 2) enhances the pressure gradient to its northwest resulting in a more intense front; and 3) induces anomalous warming of the South China Sea surface through increased downwelling, which leads to a higher moisture supply to the rain area. A positive feedback from the strong monsoon rainfall also appears to occur, leading to an intensified anomalous anticyclone near the monsoon region. This SST-subtropical ridge-monsoon rainfall relationship is observed in both the interannual timescale within each interdecadal period and in the interdecadal scale. The SST anomalies (SSTAs) change sign in northern spring and resemble a tropospheric biennial oscillation (TBO) pattern during the first interdecadal period (1951-77). In the second interdecadal period (1978-96) the sign change occurs in northern fall and the TBO pattern in the equatorial eastern Pacific SST is replaced by longer timescales. This interdecadal variation of the monsoon-SST relationship results from the interdecadal change of the background state of the coupled ocean-atmosphere system. This difference gives rise to the different degrees of importance of the feedback from the anomalous circulations near the monsoon region to the equatorial eastern Pacific. In a wet monsoon year, the anomalous easterly winds south of the monsoon-enhanced anomalous anticyclone start to propagate slowly eastward toward the eastern Pacific in May and June, apparently as a result of an atmosphere-ocean coupled wave motion. These anomalous easterlies carry with them a cooling effect on the ocean surface. In 1951-77 this effect is insignificant as the equatorial eastern Pacific SSTAs, already change from warm to cold in northern spring, probably as a result of negative feedback processes discussed in ENSO mechanisms. In 1978-96 the equatorial eastern Pacific has a warmer mean SST. A stronger positive feedback between SSTA and the Walker circulation during a warm phase tends to keep the SSTA warm until northern fall, when the eastward-propagating anomalous easterly winds reach the eastern Pacific and reverse the SSTA.

Chang, C. P., Y. Zhang, et al. (2000). "Interannual and interdecadal variations of the East Asian summer monsoon and tropical Pacific SSTs. Part II: Meridional structure of the monsoon." Journal of Climate, Boston, MA 13(24): 4326-4340.

The relationship between the interannual variations of the East Asian summer monsoon and that of the tropical SST shows considerable variations. In this study, rainfall in the southeastern coastal area of China (SEC) during 1951-96 is used to composite the tropical SST, 850-hPa wind, and 500-hPa height. The results relative to the May-June rainfall, which represents most of the SEC summer monsoon rainfall, are compared to the Yangtze River Valley (YRV) rainfall composites. It is shown that strong interdecadal changes in the Pacific may account for the observed variations in the meridional structure of the monsoon-SST relationship. The western Pacific 500-hPa subtropical ridge, which is influenced by the equatorial eastern Pacific SST, is crucial to these variations. During 1951-77 the SEC wet phase is produced by an anomalous anticyclone in the northern South China Sea, which tends to make the monsoon pre-Mei-yu and Mei-yu fronts quasi-stationary in the general area of both SEC and YRV, and also helps to warm the SST in the northern South China Sea. In this case the monsoon rainfalls in the two regions are in phase. During 1978-96 the mean equatorial eastern Pacific SST is higher, leading to a stronger and more expansive mean western Pacific subtropical ridge. Its proximity to the SEC region causes the latter to experience a strong interdecadal change, with less mean rainfall than 1951-77. Within the 1978-96 period, the anomalous anticyclone sustaining the YRV wet phase is situated near SEC, suppressing the SEC rainfall. Therefore the SEC and YRV rainfalls become out of phase. The SEC wet phase in 1978-96 depends on an anomalous 850-hPa cyclone in the East China Sea. This anomalous cyclone, which transports moist air onshore from the east resulting in maximum moisture convergence in SEC, develops when the western Pacific subtropical ridge is weak and displaced equatorward. The flow is more baroclinic and the monsoon fronts are active in the southeast coastal area. In this case the SEC and YRV rainfalls are uncorrelated. The July and August SEC wet phases show opposite characteristics. The wet July phase depends on anomalous 850-hPa cyclonic circulation in the northern South China Sea (and the East China Sea during 1951-77), which requires a retreat of the western edge of the western Pacific subtropical ridge. The anomalous South China Sea cyclone may be due to more frequent tropical cyclone activity. This is in contrast to the wet August phase, which is associated with anomalous anticyclones in the northern South China Sea and a greater westward extension of the subtropical ridge.

Chattopadhyay, J. and R. Bhatla (1994). "The interannual variability of mid-latitude meridional circulation and its teleconnection with Indian monsoon activity." Proceedings, Bangalore, India 103(3): 369-382.

The statistical relationship between the summer monsoon rainfall over all India, northwest India and peninsular India, onset dates of monsoon and the index of mid latitude, (35 degrees to 70 degrees N) meridonal circulation at 500 hPa level over different sectors and hemisphere based on 19 years (1971-1989) data, have been examined. The results indicate that (i) the summer monsoon rainfalls over all India, northwest India and peninsular India show a significant inverse relationship with the strength of meridional index during previous January over sector 45 degrees W to 90 degrees E. (ii) The summer monsoon rainfalls over all India and peninsular India show a significant inverse relationship with the strength of meridonal index during previous December over sector 90 degrees E to 160 degrees E. (iii) The summer monsoon rainfall over northwest India shows a significant direct relationship with the meridional index during previous May over sector 160 degrees E to 45 degrees W. Significant negative relationships are also observed between the meridional circulation indices of previous October (sector 3 and 4), previous December (sectors 1, 3 and 4), previous winter season (sector 3 and 4) and the onset dates of summer monsoon over India. The meridional circulation index thus can have some possible use for long range forecasting of monsoon rainfall over all India, northwest India and peninsular India, as well as the onset dates of monsoon.

Cheang, B.-K. (1993). "Interannual variability of monsoons in Malaysia and its relationship with ENSO." Proceedings, Bangalore, India 102(1): 219-239.

Interannual variation of monsoons has been studied utilising homogeneous rainfall records of 41 years (1951-1991) from Malaysia and upper air data of stations in Asia, Australia and the western Pacific. Sources of upper air data are the U.S. Department of Commerce and Kuala Lumpur Northern Winter Monsoon Activity Centre. Extreme wet and dry years have been identified and the influence of ENSO on Maylaysian annual rainfall has been discussed. Influence of ENSO on the performance of northern summer and winter monsoons has also been studied from Malaysian rainfall data. Further, regional circulation patterns associated with El Nino and La Nina years have also been identified. No linear trend has been found in the annual rainfall of 16 stations in Malaysia. Most El Nino years are associated with below median and La Nina years with above median rainfall at most stations in Malaysia. ENSO has greater influence over east Malaysia than peninsular Malaysia. Interannual variability of rainfall with reference to ENSO conditions has been discussed in details. Also, circulation features have been identified to foresee El Nino/LaNina events.

Chen, G. T.-J. (1989). "Overview of Mei-yu research in Taiwan." Sham, P. and Chang, C. P.

Mei-yu (or Baiu) is a unique regional weather and climate phenomenon over East Asia and the western North Pacific. It occurs in the period of late spring to early summer when the circulation regime over the area changes from the northeast monsoon in winter to the southwest monsoon in summer. The mean position of this phenomenon migrates northward with time. It occurs over southern China and the Taiwan area in the period of mid-May to mid-June. The main purpose of this paper is to review and look ahead at the Mei-yu research work that has been done and will be done by Taiwan meteorologists. Research work for the Mei-yu over southern China and the Yangtze River Basin was mostly not included. The primary focus of this paper is the basic and applied research on various features of Mei-yu on different time and space scales. Only a very small portion of this paper is devoted to the aspect of forecast research. However, the current forecast skill of the Central Weather Bureau in heavy rainfall was evaluated and research work needed for improving the skill was suggested. The first part of this paper discussed the existence and importance of Mei-yu in Taiwan. Work on synoptic and climatological aspects of the Mei-yu system was then reviewed. Studies of interannual variability of Mei-yu were also included. Investigations of the characteristics of mesoscale convective systems (MCS's) as well as the environmental conditions and mesoscale triggering mechanisms for the formation and evolution of MCS's were summarized. Research of mesoscale circulation systems in the Mei-yu season, such as the Mei-yu front, low-level jet (LLJ), mesolow and outflow boundary, and topographical effect was also discussed. Finally, the field-phase of the ``Taiwan Area Mesoscale Experiment (TAMEX)'' was presented.

Chen, G. T.-J. and B. J.-D. Jou (1988). "Interannual variations of the relevant large-scale circulations during the Taiwan mei-yu seasons." Papers in Meteorological Research, Taipei, Taiwan 11(2): 119-147.

The interannual variations of large-scale circulation patterns and the corresponding frontal events over East Asia during the Taiwan mei-yu season (May 15-June 15) of 1975-1984 were examined by using the National Center for Atmospheric Research (NCAR) objectively analyzed grid-point data and synoptic weather charts. The active-wet, inactive-dry, and quasi-normal mei-yu years were defined in terms of the normalized rainfall index, which uses rainfall observations over western Taiwan. It is found that the nonfrontal forcing, such as the local circulation associated with the local instability, may play an important role in determining the mei-yu rainfall. In consistency with the previous study, the southward movement and the southward penetration of the mei-yu front seem to be controlled mainly by the midlatitude circulation systems. The more frequent frontal activities to the southeast of Ship Tango were observed in the active mei-yu years rather than in other years. In the active mei-yu season, the common features of the circulation patterns over East Asia include midlatitude blocking over the Sea of Okhotsk/Eastern Siberia and a weaker Western Pacific Subtropical High (WPSH) or southward shift of the WPSH. Stronger low-level southwesterlies originating from the Bay of Bengal are found over Taiwan and the nearby mei-yu area. In the inactive mei-yu season, midlatitude blocking is not found, and a stronger WPSH extends westward to southeastern China. Weaker low-level southwesterlies or southerlies-southeasterlies of the WPSH circulations dominate over Taiwan and its vicinity. The upper level divergent outflows produced by the convections over the monsoon low and the mei-yu frontal area apparently constitute the upper level branches of the two local Hadley circulations over East Asia. The pronounced upper level divergent outflows from the mei-yu area to the midlatitudes suggest that the mei-yu activities may play some roles in affecting midlatitude circulation systems. It is shown that the variation of the WPSH is, at most, partially affected by the monsoon circulation through its eastward divergent outflows (Walker type).

Chen, J.-M. and M.-M. Lu (2000). "Interannual variation of the Asian-Pacific atmospheric system in association with the northern summer SST changes." TAO, Taiwan, Republic of China 11(4): 833-860.

The purpose of this study is to analyze the dynamic and hydrological characteristics of the interannual variability of the northern summer (June-August) ocean-atmosphere system in the Asian-Pacific region. In this ocean-atmosphere system, there are two types of interannual variability modes. As indicated by the sea surface temperature (SST) variability, the first type is related to the variations of the mature phase of the El Nino-Southern Oscillation (ENSO) events. Its temporal variability is characterized by alternations between the maximum phases of the El Nino and La Nina events. Its spatial structure is characterized by an elongated positive (negative) SST anomaly over the tropical eastern Pacific during the El Nino (La Nina) event. The second type is related to SST variability between the developing and decaying stages of the ENSO events. This mode is characterized by warm (cold) SST anomalies in the tropical central and eastern Pacific during the developing stage of the El Nino (La Nina) event, and warm (cold) SST anomalies near the Peruvian coast during the decaying stage. In accordance with these two types of interannual SST variability, tropical convection and the upward branches of Walker circulation are found enhanced (suppressed) in association with the warm (cold) SST anomalies. The centers of tropical convection anomaly coincide well spatially with the centers of major vertical motion branches and SST anomalies in the tropical western Pacific. The centers are to the west of the centers of vertical motion branches and SST anomalies in the central and eastern Pacific. In the atmospheric system, the lower-tropospheric circulation anomalies corresponding to the first interannual mode contain spatial structures largely opposite to the climatological mean circulation. These anomalies represent the weaker Asian low and Pacific subtropical high during the El Nino event, which lead to weaker tropical monsoon westerlies and Pacific trade winds. The lower-tropospheric circulation anomalies corresponding to the second interannual mode are characterized by an anomalous low centered in the western Pacific during the developing stage of the El Nino event. This anomalous low later develops into an anomalous high during the decaying stage. For both types of interannual mode, water vapor convergence toward the convection-enhanced region is observed. Such convergence results in an increase in atmospheric water vapor and thus maintains the positive precipitation anomalies. Enhanced precipitation and tropical convection are found embedded in the lower-tropospheric anomalous lows and accompanied by intensified transient activity. Water vapor divergence, negative precipitation anomaly, and weaker transient activity are found for the convection-suppressed region.

Chen, L. (1991). "Lag association between snow cover over Qinghai-Xizang plateau and monsoon rainfall in South China applied to long-range weather forecasting." Programme on Long Range Forecasting Research.

The application of snow cover as a predictor in long-range weather prediction is considered. A discussion covers the interannual variability in the winter-spring snow cover over the Qinghai-Xizang plateau; the influence on the summer circulation over Eastern Asia; and the influence on the early monsoon rainfall in Southern China. For the application of the aforementioned relationships to long-range forecasting of snow cover, a regression equation is derived for a snow cover index S from 1956 to 1975 data: S=-3.5+0.4R-24.8T, where R is the winter rainfall; and T, the air temperature. The agreement of forecasts with observations is demonstrated.

Chen, L. (1993). "Zonal sea surface temperature anomaly in the tropical Indo-Pacific Ocean and its effect on the summer Asian monsoon." Institute of Atmospheric Physics, Frontiers in atmospheric sciences., New York, NY, Allerton Press, Inc.

In this paper, the main features of the zonal distribution of sea surface temperature (SST) anomalies in the tropical Indo-Pacific Ocean area and its interannual variability are discussed. It is shown that there is a strong reverse-direction relationship in east-west SST anomaly gradients between the Indian Ocean and the Pacific Ocean. The zonal distribution of SST anomalies in the Indo-Pacific Ocean area could be classified into two distinct basic patterns, in one there are negative anomalies over the western Indian Ocean and the eastern Pacific Ocean and positive anomalies from the eastern Indian Ocean to the western Pacific Ocean, while in the other there is a distribution opposite of the previous one. Furthermore, the differences in summer Asian monsoon circulation associated with the two SST anomaly patterns are analyzed. It is suggested that the opposite direction east-west SST anomaly gradient relationship between the tropical Indian Ocean and the Pacific Ocean could be an important factor in producing the out-of-phase tendency of interannual variabilities between the Indian and East Asian monsoon systems.

Chen, L. (1994). "Draft proposal for the South China Sea monsoon Experiment (SCSMEX)." Annual Report, Beijing, China.

In this document, a South China Sea Monsoon Experiment (SCSMEX) is proposed to provide the requisite observations needed for a better understanding of the mechanism for the earliest onset phase of the boreal summer monsoon, aiming to improve prediction of the monsoon over southeast Asia and southern China. Emphases will also be on understanding the large scale circulation and convective system over the South China Sea and their relationships with the interannual variability of the monsoon ocean-atmosphere coupled system. SCSMEX will be fully coordinated with the GEWEX Asian Monsoon Experiment (GAME) and the MOnsoon Numerical Experiment Group (MONEG), both sponsored by the World Climate Research Program (WCRP).

Chen, L., M. Dong, et al. (1992). "The characteristics of interannual variations on the East Asian monsoon." Journal of the Meteorological Society of Japan, Tokyo, Japan 70(1B): 397-421.

By utilizing the meteorological observational data over the mainland of China and surrounding oceans from 1951 to 1990, the characteristics of the climatic trend of East Asian monsoon and the interannual variation of monsoon overlapped on the general trend have been studied. The results show that during the past 40 years, especially in the 1980s, China has generally been drying and the areas south of 35 degrees N in China are getting cooler. This may be attributed to the weakening of the winter and summer monsoon in China. Mei-yu in middle and lower reaches of Yangtze River and the precipitation in other areas of China are affected by the climatic change trend. It has long been believed that the Indian Monsoon is correlative to the summer precipitation of China. But in our studies, it can be concluded that there is a significant correlation only between the summer precipitation over India and that over the western part of North China, and for other areas of China the correlation is not obvious. The interannual anomaly of the summer monsoon in China is mainly attributed to the variation of each member of the circulation system of the East Asian summer monsoon. The interactions of air-sea and air-land have also been discussed. Although a significant correlation cannot be found between the SST of equatorial eastern Pacific/Polar ice and the winter/summer monsoon of China, they all have similar significant interannual oscillations and the correlation between these interannual oscillation components of the same frequency is very high.

Chen, L. and R. Wu (2000). "Interannual and decadal variations of snow cover over Qinghai-Xizang Plateau and their relationships to summer monsoon rainfall in China." Advances in Atmospheric Sciences, Beijing, China 17(1): 18-30.

Interannual and decadal variations of winter snow cover over the Qinghai-Xizang Plateau (QXP) are analyzed by using monthly mean snow depth data set of 60 stations over QXP for the period of 1958 through 1992. It is found that the winter snow cover over QXP bears a pronounced quasi-biennial oscillation, and it underwent an obvious decadal transition from a poor snow cover period to a rich snow cover period in the late 1970's during the last 40 years. It is shown that the summer rainfall in the eastern China is closely associated with the winter snow cover over QXP not only in the interannual variation but also in the decadal variation. A clear relationship exists in the quasi-biennial oscillation between the summer rainfall in the northern part of North China and the southern China and the winter snow cover over QXP. Furthermore, the summer rainfall in the four climate divisions of Qinling-Daba Mountains, the Yangtze-Huaihe River Plain, the upper and lower reaches of the Yangtze River showed a remarkable transition from drought period to rainy period in the end of 1970's, in good correspondence with the decadal transition of the winter snow cover over QXP.

Chen, L.-t. (1991). "Relationship between the Northern Oscillation and monsoon rainfall in East China and air temperature in North America." Chinese Science Bulletin, Beijing, China 36(7): 592-596.

In the present study, for the intensity of NO the difference between monthly mean SLP anomalies at stations of Ship N (31 degrees N, 140 degrees W) and Manila (14 degrees 31'N, 121 degrees E) is used, which is called the Northern Oscillation Index (NOI). The empirical orthogonal function (EOF) analysis has shown that the interannual variabilities of SLP anomaly at the two single stations are representative in space and could be used to describe the large-scale nature of the NO. The time variations of the normalized rainfall are shown, averaged for June-July in the lower and middle reaches of the Yangtze River and the NOI averaged for March-May in the period of 1954-1983. Comparing the sign of anomaly with that of the NOI for each year in the two time series, we can see that among 30 years, 21 show the same sign and 9 show the opposite sign, indicating more chance of in-phase relationship (about 70%) than an out-of-phase one. If it is counted according to two classes of positive and negative NOI, out of the 30 years, 16 are with positive index and 14 with a negative one. The former has 11 years of the same sign and 5 of the opposite sign to the rainfall anomaly, the latter has 10 years of the same sign and 4 of the opposite sign to the rainfall anomaly. Both the chances of in-phase relationship are also about 70%. Again, if we focus our attention on the condition of 9 years of the opposite sign, i.e. 1961, 1967, 1971, 1976, 1981 in positive NOI and 1954, 1969, 1980, 1983 in negative NOI, it can be seen that all the opposite sign phenomena appeared in the years with maximum or minimum NOI.

Chen, T.-C. and H. van Loon (1986). "On the interannual variation of [a] tropical easterly jet." World Meteorological Organization, Geneva, Programme on Long-Range Forecasting, Research Report Series 1986 1(6): 388-396.

In view of the fact that studies have indicated that the anomalous warming that occurred over the Central Pacific during an El Nino year may alter the synoptic structure of the E-W Walker circulation and the local Hadley circulation, the possibility is investigated that this change may, in turn, cause the alteration of the Indian monsoon circulation and the interannual variation of the tropical easterly jet. Data in which the divergent winds were well preserved were used, since the divergent components of the upper wind fields that describe the E-W Walker circulation and the local Hadley circulation are crucial to this study. The local maintenance of the tropical easterly jet is illustrated in terms of the energetics analysis of the kinetic energy equation. From the results, it is concluded that, during El Nino years, the E-W Walker circulation and the local Hadley circulation associated with the Asiatic monsoon are shifted eastward, and divergent circulations extending from South America to equatorial Africa are weakened. The low-level monsoon circulation over the Indian Ocean is suppressed because of the upward branch of the E-W Walker circulation. Being short of moisture supply, the cumulus convection activities and rainfall over the Indian subcontinent become less and result in a weaker Tibetan high. The energetic maintenance of the tropical easterly jet west of India is attributed to the convergence of kinetic energy flux by the local Hadley and E-W Walker circulations. The variation of the E-W Walker circulation over the Asiatic monsoon and the reduction of the Tibetan high intensity during the El Nino years result in an eastward-shifting of the convergent center of divergent kinetic energy flux. Furthermore, the weakening of the divergent circulations causes the alteration of divergent kinetic energy flux in such a way that the energetic support of the tropical easterly jet is reduced.

Chen, T.-C. and H. Van Loon (1987). "Interannual variation of the tropical easterly jet." Monthly Weather Review, Boston 115(8): 1739-1759.

The 200-mb tropical wind fields analyzed at Florida State University for 1965-1974 and the 200- and 700-mb tropical wind fields from the National Meteorological Center for 1979-1982 were used to explore the mechanism for the interannual variation of the tropical easterly jet. This jet is generally weaker during the summers of warm events (dry summers) in the Southern Oscillation when anomalously warm surface water appears over the eastern and central equatorial Pacific and drought occurs over the Indian subcontinent. It is observed that divergence (convergence) exists on the upstream (downstream) side of the jet. The tropical divergent circulations, i.e., the E-W Walker and the local Hadley circulations, during such summers are weakened and shifted eastward. Therefore, divergence anomalies appear in the upper troposphere over equatorial Africa or the east coast of Africa, while convergence anomalies exist over the Indian subcontinent or the Arabian Sea. These changes of the tropical divergent circulations may cause the change in the energetics maintenance of the tropical easterly jet. The analysis shows that the divergence anomalies of the divergent kinetic energy flux appear over the east coast of Africa, and the convergence anomalies of divergent kinetic energy flux appear over the Indian subcontinent. It is inferred from these anomalies of kinetic energy flux that the kinetic energy generation and destruction associated with the tropical easterly jet are less in dry summers. On the basis of these changes in the upper level tropical circulations during dry summers, a suggestion is offered that relates the anomalously warm surface water over the eastern and central equatorial Pacific to the weakening of the low-level monsoon circulation and the tropical easterly jet.

Chen, T.-C. and S.-P. Weng (1998). "Interannual variation of the summer synoptic-scale disturbance activity in the western tropical Pacific." Monthly Weather Review, Boston, MA 126(6): 1725-1733.

The authors computed the occurrence frequency of synoptic-scale disturbances over the western tropical Pacific with a simple synoptic scheme and the Goddard Earth Observing System data for 1980-94 supplemented by the 1979 National Meteorological Center (currently the National Centers for Environmental Prediction) data. The major occurrence of these disturbances exists along the monsoon trough with maximum occurrence frequency over Micronesia. The occurrence frequency distribution undergoes an interannual variation through the influence of large-scale circulation during boreal summer. As a part of the interannual variation of large-scale summer circulation in the Pacific basin, a major anomalous anticyclonic (cyclonic) circulation cell emerges in the western subtropical Pacific (north of 15 degrees N), and a minor anomalous cyclonic (anticyclonic) circulation cell appears in the western tropical Pacific (south of 15 degrees N) during warm (cold) summers. The tropical synoptic-scale disturbance activity is affected by these anomalous summer circulations in the following two ways: 1) the maximum occurrence frequency appears east (west) of 150 degrees E (the east end of the climatological monsoon trough) during warm (cold) summers, and 2) tropical synoptic-scale disturbances are located primarily south of 15 degrees N during warm summers, while their occurrences are enhanced north of 15 degrees N during cold summers. Since the effort made here is a pilot study, the authors suggest some potential investigations of tropical synoptic-scale disturbances and interannual variations of large-scale summer circulation.

Chen, T.-C. and S.-P. Weng (1999). "Interannual and intraseasonal variations in monsoon depressions and their westward-propagating predecessors." Monthly Weather Review, Boston, MA 127(6, Pt. 1): 1005-1020.

The majority of monsoon depressions develop from the regenesis of westward-propagating residual lows from the east. Most of these residual lows can be traced to weather disturbances in the south China Sea, including tropical cyclones and 12-24-day monsoon lows. Hypothetically, any mechanism causing a variation in the occurrence frequency of these two types of weather disturbances in the western tropical Pacific-south China Sea (WTP-SCS) region may result in a corresponding change in the formation frequency of monsoon depressions over the Bay of Bengal. Two such possible mechanisms are interannual and intraseasonal variations of large-scale summer circulation in the WTP-SCS region induced by 1) the interannual variation of the sea surface temperature (SST) in the eastern tropical Pacific and 2) the northward migration of the 30-60 day monsoon trough/ridge. The National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis data and the 6-hourly tropical cyclone track collected by the Japan Meteorological Agency for the period of 1979-94 were analyzed to substantiate the aforementioned hypothesis. The findings are as follows. 1) Interannual variation. Based upon the SST averaged over the National Oceanic and Atmospheric Administration NINO3 region (150 degrees -90 degrees W, 5 degrees S-5 degrees N), the summers of 1982, 1983, 1987, and 1991 and 1981, 1984, 1985, 1988, 1989, and 1994 are defined as warm and cold, respectively. A clear interannual variation can be seen in the frequency of monsoon depressions in the Bay of Bengal: an enhancement (reduction) of monsoon depression activity occurs during cold (warm) summers. This interannual variation of monsoon depression activity is traceable to the corresponding variation of the combined tropical cyclone and 12-24-day monsoon low frequency in the south China Sea. The latter interannual variation results from the development of an anomalous anticyclonic (cyclonic) circulation between 15 degrees and 30 degrees N in the WTP-SCS region in response to the warm (cold) SST anomalies in the eastern tropical Pacific. 2) Intraseasonal variation. There is an intraseasonal variability in the occurrence of tropical cyclones and of 12-24-day monsoon lows over the south China Sea, which is followed by a corresponding variability of monsoon depressions over the Bay of Bengal. The formation frequency of these depressions is dependent on the penetration role of the residual lows of these two types of disturbances across Indochina. These residual lows lead to an intraseasonal change in monsoon depression formation in connection with a deepening/filling of the monsoon trough over northern India and the Bay of Bengal.

Chen, T.-C., S.-P. Weng, et al. (1998). "Interannual variation in the tropical cyclone formation over the western North Pacific." Monthly Weather Review, Boston, MA 126(4): 1080-1090.

The interannual variation in tropical cyclone genesis frequency over the western North Pacific was examined for the active tropical cyclone (including summer and fall) during 1979-94. An emphasis was put on the possible effect of the interannual variation of atmospheric circulation and monsoon trough on tropical cyclone occurrence. The major findings of this study are the following: 1) A distinct increase (decrease) of tropical cyclone genesis frequency occurs north of the climatological location of the monsoon trough in the Philippine Sea during summers (June-August) with anomalous cold (warm) sea surface temperature (SST) over the NINO3 region. The interannual variation of tropical cyclone genesis in this region results from the appearance of an anomalous cyclonic (anticyclonic) cell situated in a summer teleconnection wave train emanating from the western tropical Pacific and progressing along the rim of the North Pacific. In addition to the north-south interannual variation, there is also a longitudinal interannual variation in the summer tropical cyclone genesis frequency over this region. The contrast of tropical cyclone genesis between the regions west and east of 150 degrees E is reduced (enhanced) when the monsoon trough extends (retreats) eastward (westward) across this longitude during warm (cold) summers. 2) For fall (September-November), there is no clear relationship between the north-south interannual variation in the tropical cyclone genesis over the western North Pacific and SST (NINO3). However, there is a perceptible tendency of the longitudinal interannual variation in tropical cyclone genesis frequency to follow the eastward extension /westward retreat of the monsoon trough in a way such as it does during the summer season.

Chen, T.-C. and M.-C. Yen (1994). "Interannual variation of the Indian monsoon simulated by the NCAR Community Climate Model: effect of the tropical Pacific SST." Journal of Climate, Boston, MA 7(9): 1403-1415.

Previous studies have shown diagnostically and statistically that the interannual variation of the Indian monsoon is closely correlated with the tropical Pacific sea surface temperature (SST). It seems likely that the interannual variation of the Indian monsoon results from the response of this monsoon system to the interannual variations of the Pacific SST. This hypothesis has not been substantiated in the past. In order to test it, Version 1 of the National Center for Atmospheric Research Community Climate Model (CCM) was used to perform two parallel climate simulations: a control run using the 12 calendar month climatological SST and a run using real-time Pacific SST. The SST data used in this study are derived from the Comprehensive Ocean-Atmosphere Data Set. Significant interannual variations of the Indian monsoon circulation are generated by the real-time Pacific SST experiment, but not the climatological SST control experiment. In particular, the model monsoon of the real-time Pacific SST simulation weakened during the 1982 and 1987 summers and intensified in the 1984 and 1988 summers. The interannual variation of the model monsoon circulation resembles the observed in many ways. According to the linear theory of Matsuno and Gill, summertime stationary eddies are generated by steady tropical forcing. Because the Indian monsoon is a part of summertime stationary eddies, interannual variation of steady tropical heating induced by interannual Pacific SST anomalies results in interannual variations of summertime stationary eddies and the associated monsoon. Various diagnostic analyses are thus engaged to illustrate this explanation of the monsoon interannual variation.

Chen, T.-C. and J.-H. Yoon (2000). "Interannual variation in Indochina summer monsoon rainfall: possible mechanism." Journal of Climate, Boston, MA 13(11): 1979-1986.

Indochina is located between two extensively researched components of the Asian monsoon system: the Indian subcontinent and southeast-east Asia. Highly correlated with the National Oceanic and Atmospheric Administration Nino-3 sea surface temperatures, the interannual variation of Indochina monsoon rainfall is caused by a mechanism different from the two aforementioned regions. This mechanism consists of two elements: 1) the interannual modulation of the occurrence frequency of westward-propagating weather disturbances in the South China Sea-western tropical Pacific by an anomalous short-wave train emanating from the western tropical Pacific, and 2) an east-west interannual seesaw of the global divergent water vapor flux induced by the interannual variation in the global divergent circulation. An effort is made in this study to illustrate this mechanism.

Chen, W. and H.-F. Graf (1998). "The interannual variability of East Asian winter monsoon and its relation to global circulation." Hanburg, Germany, Max Planck Institut fuer Meteorologie 35.

The interannual variability of East Asian winter monsoon (EAWM) is studied based on a monsoon intensity index with the data from the NCEP/NCAR reanalysis for the period of 1968-1997. The results show that both the regional Hadley circulation along the East Asian coast and the Walker Circulation over equatorial latitudes are more intense in a strong monsoon winter than in a weak monsoon winter. This difference corresponds to the shift of major tropical convection centres. In a strong monsoon winter the convection is much enhanced over the maritime continent and reduced over the central Pacific; the situation is reverse in a weak monsoon winter. These anomalous heat source distributions force opposite phases of the PNA pattern. It is suggested that the barotropic instability of the extratropical zonal flow, which is associated with the interannual variation of EAWM, is important for the propagation of stationary waves along the route of the PNA pattern. There also seems to be a stationary wave originating over the tropical western Pacific which propagates eastward and reaches the central and eastern Pacific during strong monsoon winters. The lag-correlations between the EAWM intensity index and tropical Pacific sea surface temperature anomaly (SSTA) indicate that the interannual variability of EAWM is mainly influenced by the SSTAs over the tropical Pacific of the preceeding summer. These SSTAs disappear in the following spring. Generally a cool (warm) sea surface temperature in the tropical central and eastern Pacific corresponds to a strong (weak) EAWM. Thus the processes of tropical ocean-atmosphere interactions are suggested to be the dominant mechanism which influence the interannual variations of EAWM. However, the instability processes at midlatitudes can also cause anomalous winter monsoon, such as the 76/77 and 78/79 winter. On the other hand, the SSTA in the South China Sea has been shown to be influenced mainly by the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm that an anomalous East Asian summer monsoon is closely related to the preceding EAWM.

Chen, W., H.-F. Graf, et al. (2000). "The interannual variability of East Asian winter monsoon and its relation to the summer monsoon." Advances in Atmospheric Sciences, Beijing, China 17(1): 48-60.

Based on the NCEP/NCAR reanalysis data the interannual variability of the East Asian winter monsoon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon include strong (weak) northerly winds along coastal East Asia, cold (warm) East Asian continent and surrounding sea and warm (cold) ocean from the subtropical central Pacific to the tropical western Pacific, high (low) pressure in East Asian continent and low (high) pressure in the adjacent ocean and deep (weak) East Asian trough at 500 hPa. These interannual variations are shown to be closely connected to the SST anomaly in the tropical Pacific, both in the western and eastern Pacific. The results suggest that the strength of the EAWM is mainly influenced by the processes associated with the SST anomaly over the tropical Pacific. The EAWM generally becomes weak when there is a positive SST anomaly in the tropical eastern Pacific (El Nino), and it becomes strong when there is a negative SST anomaly (La Nina). Moreover, the SST anomaly in the South China Sea is found to be closely related to the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm the connection between the EAWM and the following East Asian summer monsoon. The possible reason for the recent 1998 summer flood in China is briefly discussed too.

Chia, H. H. and C. F. Ropelewski (2002). "The Interannual Variability in the Genesis Location of Tropical Cyclones in the Northwest Pacific." Journal of Climate 15(20): 2934-2944.

Variations in the seasonal mean (July-October) genesis positions of tropical cyclones (TCs) in the western North Pacific associated with variations in the large-scale atmospheric circulation are investigated. Analysis shows considerable interannual variability in the seasonal TC mean genesis positions (MGPs) during the 1979-99 period. The variability is shown to be related to the 200-850-hPa vertical wind shear, the west Pacific sea surface temperature (SST), the position and strength of the monsoon trough, and the position and strength of the western Pacific subtropical high (WPSH). Each of these circulation features as well as the SST is, in turn, related to the El Nino-Southern Oscillation (ENSO). However, while this study suggests that ENSO is a major factor in determining seasonal MGP, the relatively short satellite observational period also suggests that ENSO is not the sole determinant, the La Nina year of 1988 being one example. The study further suggests that the role of ENSO is complicated by the differences in the timing and evolution of individual ENSOs with respect to the peak in the mean annual cycle of the TC genesis.

Chongyin, L. and M. Mingquan (2001). "The Influence of the Indian Ocean Dipole on Atmospheric Circulation and Climate." Advances in Atmospheric Sciences 18(5): 831-843.

The SST variation in the equatorial Indian Ocean is studied with special interest in analyzing its dipole oscillation feature. The dipole oscillation appears to be stronger in September-November and weaker in January-April with higher SST in the west region and lower SST in the east region as the positive phase and higher SST in the east region and lower SST in the west region as the negative phase. Generally, the amplitude of the positive phase is larger than the negative phase. The interannual variation (4-5 year period) and the interdecadal variation (25-30 year period) also exist in the dipole. The analyses also showed the significant impact of the Indian Ocean dipole on the Asian monsoon activity, because the lower tropospheric wind fields over the Southern Asia, the Tibetan high in the upper troposphere and the subtropical high over the northwestern Pacific are all related to the Indian Ocean dipole. On the other, the Indian Ocean dipole still has significant impact on atmospheric circulation and climate in North America and the southern Indian Ocean region (including Australia and South Africa).

Chou, M.-D., P.-K. Chan, et al. (2001). "A sea surface radiation data set for climate applications in the tropical western Pacific and South China Sea." Journal of Geophysical Research. D. Atmospheres 106(D7): 7219-7228.

The sea surface shortwave and longwave radiative fluxes have been retrieved from the radiances measured by Japan's Geostationary Meteorological Satellite 5. The surface radiation data set covers the domain 40 degree S-40 degree N and 90 degree E-170 degree W and a period starting from January 1998. The temporal resolution is 1 day, and the spatial resolution is 0.5 degree x0.5 degree latitude- longitude. The retrieved surface radiation has been validated with the radiometric measurements at the Atmospheric Radiation Measurement (ARM) site on Manus Island in the equatorial western Pacific. It has also been validated with the measurements at the radiation site on Dungsha Island during the South China Sea Monsoon Experiment (SCSMEX) (May and June 1998). The data set is used to study the effect of El Nino and East Asian summer monsoon on the heating of the ocean. Interannual variations of clouds associated with El Nino and the East Asian summer monsoon have a large impact on the radiative heating of the ocean, exceeding 40 W m super(-2) in seasonal mean over large areas. Together with the Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes at the top of the atmosphere and the radiative transfer calculations of clear-sky fluxes, this surface radiation data set is also used to study the impact of clouds on the solar heating of the atmosphere. It is found that clouds enhance the atmospheric solar heating by similar to 21 W m super(-2) in the tropical western Pacific and the South China Sea.

Chu, P. C., S. Lu, et al. (1997). "Temporal and spatial variabilities of the South China Sea surface temperature anomaly." Journal of Geophysical Research, Washington, DC 102(C9): 20937-20955.

In this study we use the National Centers for Environmental Prediction (NCEP) monthly sea surface temperature (SST) fields (1982-1994) to investigate the temporal and spatial variabilities of the South China Sea (SCS) warm/cool anomalies. Three steps of analysis were performed on the data set: ensemble mean (T), composite analysis to obtain the monthly mean anomaly relative to the ensemble mean (T), and empirical orthogonal function (EOF) analysis on the residue data relative to (T)+(T). The ensemble mean SST field (T) has a rather weak horizontal gradient: 29 degrees C near the Borneo coast to 25 degrees -26 degrees C near the southeast China coast. Two areas of evident SST anomalies were found in the monthly T variation: west of Borneo-Palawan Islands (WBP) and southeast of the southern Vietnam coast (SVC). Four patterns, monsoon and transition each with two out-of-phase structures, were found. During the spring-to-summer transition (March to May) the warm anomaly is formed in the northern SCS with T>1.8 degrees C located at 112 degrees -119 degrees 30'E, 15 degrees -19 degrees 30'N. During the fall-to-winter transition (October to November) the northern SCS (north of 12 degrees N) cool anomaly is formed in November with T<-0.6 degrees C located at 108 degrees -115 degrees E, 13 degrees -20 degrees N. We performed an EOF analysis on the residue data relative to T+T in order to obtain transient and interannual variations of the SST fields. EOF1 accounts for 47% of the variance and represents the northern SCS warm/cool anomaly pattern. EOF2 accounts for 14% of the variance and represents the southern SCS dipole pattern. Strong northern SCS warm anomaly (1 degrees C warmer) appears during October-November 1987 and January-February 1988, and strong northern SCS cool anomaly (1 degrees C cooler) occurs during March 1986 and November 1992. Furthermore, a strong cross correlation between wind stress curl and SST anomalies, computed from the European Centre for Medium-Range Weather Forecast analyzed wind stress data and the NCEP SST data for different lags, shows the existence of an air-sea feedback mechanism in the SCS deep basin.

Chu, P. C., H.-C. Tseng, et al. (1997). "South China Sea warm pool detected in spring from the Navy's Master Oceanographic Observational Data Set (MOODS)." Journal of Geophysical Research, Washington, DC 102(C7): 15761-15771.

A South China Sea warm pool with sea surface temperature (SST) higher than 29.5 degrees C, recently reported by Chu and Chang [1995a, b] and Chu et al. [1997], appears in the central South China Sea (west of the Luzon Island) in boreal spring, strengthens until the onset of the summer monsoon (mid-May), and then weakens and disappears at the end of May. The transient features and interannual variabilities of the warm pool have not yet been studied. Here we use a subset of the U.S. Navy's Master Oceanographic Observation Data Set (MOODS) to investigate the surface thermal features. First, we employed an optimal interpolation scheme to build up a 10-day interval synoptic data set for December 1963 to November 1984 on a 0.5 degrees x 1 degrees grids (finer resolution in zonal direction) from the MOODS SST data. An ensemble mean SST field (T[idential] ) was established with a rather weak horizontal gradient (28.5 degrees C near the Palawan Island to 26 degrees C near the southeast China coast). Second, we performed a composite analysis to obtain the averaged SST anomaly field T similar to deviating from the ensemble mean for the winter and spring seasons (December-May). During December-March, T similar to is negative almost everywhere throughout the whole South China Sea. In early April, positive T similar to with closed isoline (warm pool) was evident west of Luzon Island. In May, the central SCS warm anomaly becomes stronger. On May 11-20, the central SCS warm pool (114 degrees -119 degrees E, 14 degrees -19 degrees N) has T similar to >1.8 degrees C. The size of the warm pool is around 200,000 km super(2) . Third, we performed an empirical orthogonal function (EOF) analysis on the residue data (T), deviating from T[idential] +T similar to , for the winter and spring seasons, in order to obtain transient and interannual variations of the SST fields. EOF1 accounts for 35.5% of the variance and resembles the ensemble mean pattern of nearly parallel contours with a maximum value in the southeast and a minimum value in the northwest. EOF2 accounts for 21.4% of the variance and is characterized by a warm/cool pool (116 degrees -118 degrees E, 16 degrees -18 degrees N) west of the Luzon Island. The corresponding principal component (PC sub(2) ) has strong interannual variability with a maximum value of 10 on February 11-20, 1965 and a minimum of -12 on March 21-31, 1964. This indicates the appearance of either a warm pool with a maximum strength of 1.2 degrees C or a cool pool with a maximum strength of -1 degrees C. Combination of T similar to and PC sub(2) x EOF2 leads to an occurrence of a central SCS warm pool from April to May with a warm anomaly varying between 0.8 degrees and 3 degrees C.

Chung, C. and S. Nigam (1999). "Asian summer monsoonAENSO feedback on the Cane-Zebiak model ENSO." Journal of Climate, Boston, MA 12(9): 2787-2807.

The Asian summer monsoon heating anomalies are parameterized in terms of the concurrent ENSO SST anomalies and used as additional forcing in the Cane-Zebiak (CZ) Pacific ocean-atmosphere anomaly model. The Asian heating parameterization is developed from the rotated principal component analysis of combined interannual variability of the tropical Pacific SSTs, residually diagnosed tropical diabatic heating at 400 mb (from ECMWF's analyses), and the 1000-mb tropical winds during the 1979-97 summer months of June, July, and August. Analysis of the 95 000-yr-long model integrations conducted with and without the interactive Asian sector heating anomalies reveals that their influence on the Pacific surface winds leads to increased ENSO occurrence--an extra ENSO event every 20 yr or so. An examination of the ENSO distribution w.r.t. the peak SST anomaly in the eastern equatorial Pacific shows increased El Nino occurrence in the 2.2-3.6 K range (and -1.0 to -1.6 K range in case of cold events) along with a modest reduction in the 0.6-1.2 K range, that is, a population shift due to the strengthening of weak El Ninos in the monsoon run. The interaction of ENSO-related Asian summer monsoon heating with the CZ model's ocean-atmosphere also results in a wider period distribution of ENSO variability, but with the El Nino peak phase remaining seasonally locked with the northern winter months. The above modeling results confirm the positive feedback between Asian summer monsoon and ENSO suggested by previous empirical and diagnostic modeling studies; the feedback is generated primarily by the diabatic heating changes in the Asian Tropics.

Cole, J. E., G. T. Shen, et al. (1992). "Coral monitors of El Nino/Southern Oscillation dynamics across the equatorial Pacific." Diaz, Henry F. and Markgraf, Vera.

Variability in the El Nino/Southern Oscillation (ENSO) system generates most of the interannual variability observed in global climate, yet its long-term history in the equatorial Pacific remains poorly documented. The fundamental dynamic components of ENSO variability in the equatorial Pacific include interannual changes in upwelling, atmospheric convection, and wind speed and direction. These processes are integral physical components of ENSO variability, and they produce distinct thermal and chemical signals in the surface ocean. Shallow-growing corals from sensitive Pacific sites incorporate these anomalies in the isotropic and trace metal chemistry of their aragonite skeletons. Short ( similar to 20 yr) coral records provide independent monitors of the ENSO system at three sites across the Pacific basin: the Galapagos (1 degrees S, 91 degrees W), Tarawa Atoll (1 degrees N, 173 degrees E), and Bali (8 degrees S, 115 degrees E). Galapagos Cd/Ca, Ba/Ca, and delta super(1) super(8) O records reflect the degree of regional upwelling in the eastern Pacific, which is suppressed during warm ENSO conditions. Oxygen isotropic data from Tarawa Atoll corals record the intense precipitation that the eastward displacement of the Indonesian Low brings to this region during warm ENSO periods. An independent record of Mn/Ca from one of these corals reflects the weakening and reversal of the trade winds that may trigger the onset of warm ENSO conditions basinwide. Finally, delta super(1) super(8) O from a Bali coral reflects the weakening of the Indonesian monsoon associated with warm ENSO periods. The isotopic and trace metal records from these three sites illustrate how chemical records from coral skeletons yield previously unobtainable information on dynamic aspects of ENSO variability, in many cases at monthly resolution. Individually, each of these records closely monitors an important ENSO component: SST, rainfall, winds, and upwelling. Together they provide information on the variability of climatic and oceanographic anomalies throughout the tropical Pacific, including the spatial patterns of evolution and recurrence of both warm-and cool-phase ENSO anomalies. Living corals that reach hundreds of years in age and fossil corals spanning thousands of years are available throughout the Pacific, enabling high resolution ENSO reconstructions under the altered climate boundary conditions of the late Pleistocene.

Corona, T. J. (1978). "Interannual variability of Northern Hemisphere precipitation." Colorado. State Univ., Ft. Collins, Environmental Research Paper Dec(16).

Forty years of monthly surface precipitation data for Northern Hemispheric land areas and two years of estimated oceanic rainfall data are processed to look for trends and interannual variability of precipitation. It is found that continental precipitation varies year to year from 3.3% for the North American summer seasons to 7.0% for the winter seasons in Europe, Asia, and North Africa. The winter in North America and summer in Europe, Asia, and North Africa vary by approximately 5.0%. In terms of volume, these percent variabilities mean a gain or loss of about 1 x 10 super(1) super(0) m super(3) of water for North America and 1 x 10 super(1) super(1) m super(3) of water for Europe, Asia, and North Africa. In addition, several long-term trends are evident in the data especially a 30-yr increasing trend for wintertime precipitation in Europe, Asia, and North Africa. The long-term trends generally agree with the strength of the u-component of the trade wind system and the African and Indian monsoon circulations. While results from satellite data are discussed, it is thought that the length of record, accuracy of the data, and the spatial resolution of the data are not suitable for obtaining an accurate estimate of oceanic precipitation.

Corti, S., F. Molteni, et al. (2000). "Predictability of snow-depth anomalies over Eurasia and associated circulation patterns." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 126(562, Pt. A): 241-262.

This study investigates the variability and predictability of snow depth anomalies over the Eurasian continent at the end of winter, as represented in 12 ensembles of General Circulation Model simulations performed at the European Centre for Medium-Range Weather Forecasts. Each ensemble includes nine integrations performed with the same prescribed sea surface temperature, but started from time-lagged initial conditions. An empirical orthogonal function (EOF) analysis shows that the leading EOF of Eurasian snow depth in March has a zonally-oriented dipole structure, with a band of positive anomalies covering northern Europe and Siberia, and negative anomalies over central Europe, the Himalayas and north China. A significant relationship is found between the positive/negative phase of this snow-depth anomaly and warm/cold El Nino Southern Oscillation events. The positive phase of the snow-depth EOF1 is associated with a wintertime circulation characterized by a strengthening of the westerly winds over Europe and Siberia; in the upper troposphere, this westerly anomaly is accompanied by negative zonal wind anomalies over Eurasia around 30-40 degrees N and positive zonal wind anomalies between the equator and 25 degrees N over Africa and south-east Asia. A good degree of predictability is found in the snow-related circulation anomalies: considering 500-hPa height, 850-hPa zonal wind and 200-hPa zonal wind, the interannual variations of the ensemble-mean fields show a correlation of 48%, 56% and 65% (respectively) with the corresponding observed anomalies over the eastern half (0 degrees to 180 degrees E) of the northern hemisphere. The tropical component of the zonal wind anomaly associated with snow-depth EOF1 is strongly predictable; it shows a marked persistence from winter to the early summer, and affects the large-scale circulation over south Asia in the early and central periods of the monsoon season.

Dahale, S. D. and S. V. Singh (1993). "Modelling of Indian monsoon rainfall series by univariate box-Jenkins type of models." Advances in Atmospheric Sciences, Beijing, China 10(2): 211-220.

The time domain approach, i.e. Autoregressive (AR) processes, of time series analysis is applied to the monsoon rainfall series of India and its two major regions, viz. North-West India and Central India. Since the original time series shows no modelable structure due to the presence of high interannual variability, a 3-point running filter is applied before exploring and fitting appropriate stochastic models. Out of several parsimonious models fitted, AR (3) is found to be most suitable. The usefulness of this fitted model is validated on an independent datum of 18 years and some skill has been noted. These models therefore can be used for low skill higher lead time forecasts of monsoons. Further, the forecasts produced through such models can be combined with other forecasts to increase the skill of monsoon forecasts.

De, U. S., S. N. Chatterjee, et al. (1988). "Low-frequency modes in summer monsoon circulation over India." Mausam, New Delhi 39(2): 167-178.

In recent years, there has been a large number of investigations on the structural features of 30-60-day oscillations during the summer monsoon of Southeast Asia. However, most of the investigations are based on the 1979 MONEX data. In this investigation, the nature of this similar to 40-day mode has been studied by using a comprehensive data set for 6 yr over the Indian subcontinent. The study reveals that the periodicity of this mode has a significant interannual variability and, during the same year, it has a strong spatial dependence. The limitations of the use of this mode in foreshadowing the changes of summer monsoon circulations over India have been discussed.

Deng, A., S. Tao, et al. (1989). "The EOF analyses of the precipitation during summer monsoon season in China." Chinese Journal of Atmospheric Sciences, New York, NY 13(3): 311-319.

In this paper, the basic climatic characteristics of the precipitation during summer monsoon season in China are studied by using the empirical orthogonal function analysis method. The month-to-month data of precipitation in the flood seasons April-September from 1951 to 1985 were used, and the 32 uniformly distributed observational stations were chosen as the study object in this work. Analyses show that the characteristic vector fields obtained and the corresponding time coefficients well represent the spatial distribution and temporal variation of precipitation during summer monsoon seasons in China, including seasonal and interannual variations. And these results provide a basis for us to study further the relationships between the precipitation patterns and physical factors such as height and SST (sea surface temperature) fields.

Ding, X., D. Zheng, et al. (2002). "Variations of the surface temperature in Hong Kong during the last century." International Journal of Climatology 22(6): 715-730.

A statistical analysis has been applied to obtain a better understanding of the variations of the surface climate in Southeast Asia. In particular, we have depicted the detailed features of the changes in the surface air temperature of Hong Kong (HK) during the past 115 years. Analysis of the time-frequency spectra of the wavelet transform indicates that although seasonal variations account for most of the temperature variations, strong signals also exist on subseasonal, interannual, and interdecadal time scales. Though the strong seasonal cycle is marked by a minimum temperature in February (and then in January) and a maximum temperature in July (and then in August), strong variations on the subseasonal and interannual time scales occur mostly in February and then in March. It is also found that a rising tendency exists in the long-recorded temperature data, with a rate of 0.09-0.15 degree C per decade. Temperature variations in HK are strongly related to changes in the regional and remote atmospheric circulation on various time scales. The East Asian monsoon circulation is the main factor controlling the seasonal cycle and the subseasonal and interannual variations of the HK temperature during winter. The subseasonal and seasonal variations of the temperature are also associated with changes in the atmospheric circulation over the North Pacific, which is closely linked to the East Asian jet stream. Strong signals are also found in both this mid-latitude circulation and the El Nino-southern oscillation phenomenon when the interannual variability of the HK temperature is apparent.

Ding, Y. (1990). "A statistical study of winter monsoons in East Asia." Chao, Jiping and Young, John A.

Utilizing the ECMWF datasets for 5 winters (Dec.-Feb.) from 1979 to 1984, a statistical study of winter monsoons in East Asia and West-Pacific has been made. The main results have been obtained as follows: (1) There are two regions of cold surges in East Asia and West-Pacific: the East China Sea and the South China Sea, and the Western Pacific to east of Phillipines. The former area is a major area of cold surge with high frequency of activity and great intensity. The cold surge is observed below 700hPa, with the maximum north winds near surface and rapidly decreasing with height. (2) Accompanying the southward penetration of cold surge, the cold air may extend southward from South China across the coastal region of Indo-China Peninsula down to the near-equatorial region. (3) Near the surface, the activity and intensity of Siberian highs are closely related to cold surges. (4) One may observe remarkable interannual variability of winter monsoon or cold surges in East Asia that may be associated with the interannual variability of Siberian highs and troughs on southern branch of westerlies.

Ding, Y., J. Lue, et al. (1990). "Interannual low-frequency oscillation of meridional winds over the equatorial Indian-Pacific Oceans." Quarterly Journal of Applied Meteorology, Beijing, China 1(1): 2-11.

Based on analysis of the meridional winds over oceanic areas and sea surface temperature for 1950-1979 extracted from the data sets of COADS, the long-term variability of the meridional winds over the equatorial Indian-Pacific Oceans and its relationship to the onset and development of El Nino events have been studied. The major results are as follows: 1. There is a great similarity between Intertropical Convergence Zone (ITCZ) over the Pacific and SST in the seasonal trend, with ITCZ and high SST found in the Southern Hemisphere in winter and in the Northern Hemisphere in summer. During El Nino years, unusual meridional winds were often observed, with significant convergence of meridional wind occurring over near-equatorial regions. 2. For the near-equatorial meridional winds, there are three types of interannual low-frequency oscillations--QBO, SO, FYO. QBO plays an important role in the unusual behavior of meridional wind for El Nino years, while SO is very important for both El Nino and cold water years. These two oscillations may fit well to the observed variation in the meridional wind. FYO may enhance the variation of meridional wind. 3. Interannual low-frequency oscillations of meridional winds originate in the Indian Ocean-Maritime Continent and coastal area of the east Pacific. Unusual activities of winter monsoon in both hemispheres and trade wind off the coastal area of the east Pacific are believed to be their major cause. 4. Monsoon-trade interaction shows up in the significant amplification of the disturbances of meridional wind while they propagate eastward from monsoon area to trade wind area.

Dong, B. and P. J. Valdes (1998). "Modelling the Asian summer monsoon rainfall and Eurasian winter/spring snow mass." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 124(552): 2567-2596.

The interannual variation of the south Asian summer monsoon is analysed based on sets of present day climate simulations using the UK Universities' Global Atmospheric Modelling Programme (UGAMP) general-circulation model with different land surface parametrization schemes, different horizontal resolutions, and sea surface temperature variations. Generally, a negative relationship is found between south Eurasian winter/spring snow mass and the amount of summer monsoon rainfall over India in all simulations. However, the significance of this relationship is dependent on the land surface parametrization scheme. The simulations using the no-flux boundary condition at the bottom of a three-layer soil model give a strong negative correlation. This inverse relationship is the strongest over north India and the foothills of the Himalayas and is statistically significant. The model results are in good agreement with observational studies. Composite analyses suggest that less winter/spring snowfall over south Eurasia is associated with a strong Indian summer monsoon, characterized by strong south-westerlies over the Arabian Sea in the lower troposphere in the June-August season and heavy precipitation in early summer over north India and the foothills of the Himalayas. In contrast, heavy winter/spring snowfall delays the onset of the Indian summer monsoon through the feedback of snowmelt, soil moisture and evaporation processes, and is associated with weak summer precipitation over the two regions. Sensitivity studies confirm that the snow mass-Indian monsoon relationship identified in the simulation at T42 is also robust in the simulation at T31. However, a negative relationship does not exist in the simulation at T21, indicating the importance of horizontal resolution in maintaining the snow-monsoon relationship in the UGAMP model.

Douville, H. (2002). "Influence of Soil Moisture on the Asian and African Monsoons. Part II: Interannual Variability." Journal of Climate 15(7): 701-720.

The relevance of soil moisture (SM) for simulating the interannual climate variability has not been much investigated until recently. Much more attention has been paid on SST anomalies, especially in the Tropics where the El Nino-Southern Oscillation represents the main mode of variability. In the present study, ensembles of atmospheric integrations based on the Action de Recherche Petit Echelle Grande Echelle (ARPEGE) climate model have been performed for two summer seasons: 1987 and 1988, respectively. The aim is to compare the relative impacts of using realistic boundary conditions of SST and SM on the simulated variability of the Asian and African monsoons. Besides control runs with interactive SM, sensitivity tests have been done in which SM is relaxed toward a state-of-the-art SM climatology, either globally or regionally over the monsoon domain. The simulations indicate that the variations of the Asian monsoon between 1987 and 1988 are mainly driven by SST anomalies. This result might be explained by the strong teleconnection with the ENSO and by a weak SM-precipitation feedback over south Asia (Part I of the study). The influence of SM is more obvious over Africa. The model needs both realistic SST and SM boundary conditions to simulate the observed variability of the Sahelian monsoon rainfall. The positive impact of the SM relaxation is not only due to a local mechanism whereby larger surface evaporation leads to larger precipitation. The best results are obtained when the relaxation is applied globally, suggesting that remote SM impacts also contribute to the improved simulation of the precipitation variability. A relationship between the Sahelian rainfall anomalies and the meridional wind anomalies over North Africa points out the possible influence of the Northern Hemisphere midlatitudes. The comparison of the low- and midtropospheric anomalies in the various pairs of experiments indicates that SM anomalies can trigger stationary waves over Europe, and thereby promote the intrusion of dry air from the midlatitudes into the Tropics. The study therefore emphasizes the relevance of SM for seasonal climate predictions, at least in summer in the Northern Hemisphere, and shows a dynamical interaction between the Tropics and extratropics.

Douville, H., F. Chauvin, et al. (2001). "Influence of Soil Moisture on the Asian and African Monsoons. Part I: Mean Monsoon and Daily Precipitation." Journal of Climate 14(11): 2381-2403.

Soil moisture responds to precipitation variability but also affects precipitation through evaporation. This two-way interaction has often been referred to as a positive feedback, since the water added to the land surface during a precipitation event leads to increased evaporation, and this in turn can lead to further rainfall. Various numerical experiments have suggested that this feedback has a major influence on tropical climate variability from the synoptic to the interannual timescale. In the present study, ensembles of seasonal simulations (March-September) have been performed in order to investigate the sensitivity of the Asian and African monsoon rainfall to regional soil moisture anomalies. After a control experiment with free-running soil moisture, other ensembles have been performed in which the soil water content is strongly constrained over a limited area, either south Asia or Sudan-Sahel. Besides idealized simulations in which soil moisture is limited by the value at the wilting point or at the field capacity, more realistic experiments are relaxed toward the Global Soil Wetness Project (GSWP) soil moisture climatology. The results show a different sensitivity of the Asian and African monsoons to the land surface hydrology. Whereas African rainfall increases with increasing soil moisture, such a clear and homogeneous response is not found over the Indian subcontinent. Precipitation does increase over northern India as a consequence of wetter surface conditions, but the increased evaporation is counterbalanced by a reduced moisture convergence when averaging the results over the whole Indian peninsula. This contrasted behavior is partly related to the more dynamical and chaotic nature of the Asian monsoon, for which moisture convergence is about 2 times that found over Sudan-Sahel so that water recycling has a weaker influence on seasonal rainfall. It is also due to a different response of the frequency distribution of daily precipitation, and particularly to an increased number of strong convective events with decreasing soil moisture over India. Part II of the study will investigate how soil moisture also affects the interannual variability of the Asian and African monsoons.

Douville, H., F. Chauvin, et al. (2001). "Influence of soil moisture on the Asian and African monsoons. Part I: Mean monsoon and daily precipitation." Journal of Climate, Boston, MA 14(11): 2381-2403.

Soil moisture responds to precipitation variability but also affects precipitation through evaporation. This two-way interaction has often been referred to as a positive feedback, since the water added to the land surface during a precipitation event leads to increased evaporation, and this in turn can lead to further rainfall. Various numerical experiments have suggested that this feedback has a major influence on tropical climate variability from the synoptic to the interannual timescale. In the present study, ensembles of seasonal simulations (March-September) have been performed in order to investigate the sensitivity of the Asian and African monsoon rainfall to regional soil moisture anomalies. After a control experiment with free-running soil moisture, other ensembles have been performed in which the soil water content is strongly constrained over a limited area, either south Asia or Sudan-Sahel. Besides idealized simulations in which soil moisture is limited by the value at the wilting point or at the field capacity, more realistic experiments are relaxed toward the Global Soil Wetness Project (GSWP) soil moisture climatology. The results show a different sensitivity of the Asian and African monsoons to the land surface hydrology. Whereas African rainfall increases with increasing soil moisture, such a clear and homogeneous response is not found over the Indian subcontinent. Precipitation does increase over northern India as a consequence of wetter surface conditions, but the increased evaporation is counterbalanced by a reduced moisture convergence when averaging the results over the whole Indian peninsula. This contrasted behavior is partly related to the more dynamical and chaotic nature of the Asian monsoon, for which moisture convergence is about 2 times that found over Sudan-Sahel so that water recycling has a weaker influence on seasonal rainfall. It is also due to a different response of the frequency distribution of daily precipitation, and particularly to an increased number of strong convective events with decreasing soil moisture over India. Part II of the study will investigate how soil moisture also affects the interannual variability of the Asian and African monsoons.

Druyan, L. M. (1990). "General Circulation Model (GCM) studies of sub-Saharan drought." WMO Tropical Meteorological Research Programme 30(4): 109-114.

This paper summarizes a number of studies carried out by various investigators and published during 1986-1989 on the use of the General Circulation Model and the GISS model to study sub-Saharan drought. In respect to the former, they include the studies of Fulland and others on the relationship between Sahel rainfall and sea surface temperature (SST) of Palmer on the impact of the SST for the Atlantic, Pacific and Indian oceans on Sahel rainfall, etc. The GISS model was used to investigate differences between model years with abundant Sahel rainfall versus model years that evolved with very dry summers over the Sahel (Druyan), the importance of the springtime circulation pattern in the assessment of the potential impact of SST on the interannual variations of the African summer monsoon rainfall, the tracking of Sahel precipitation to its evaporative sources and the 7-month simulations (March-September) with specified monthly mean SST observed in 1958 and in 1984.

Duemenil, L. (1998). "Portrayal of the Indian summer monsoon in the land-ocean-atmosphere system of a coupled GCM." Hamburg, Germany, Max Planck Institut fuer Meteorologie 40.

A 150 year-long numerical simulation of present-day climate using the Max-Planck Institute's coupled ocean-atmosphere model ECHAM4-T42-OPYC3 is analysed with regard to the interannual variability of the strength of the Indian summer monsoon and its relation to land-surface and ocean interactions. Individual years are categorised into three classes of monsoons: normal, strong and weak (greater or less than one standard deviation of precipitation over India). The ensembles of anomalous monsoons are then sub-divided into a composite of cases coinciding with sea surface temperature (SST) anomalies in the Pacific related to the El Nino-Southern Oscillation (ENSO) phenomenon and a second composite of anomalous monsoons occurring, when no SST anomalies are found in the Pacific. The coupled model shows variations of the SST in the Pacific which are as large as and occur at a similar frequency as in observations. Thus it provides the basis for a realistic simulation of the interannual monsoon variability in ENSO-related conditions, but it overemphasizes the biennial component of occurrence. As in observations, about a third of all cases of weak monsoons occur in the summer when an El Nino begins to develop in the Pacific, while strong monsoons are often associated with La Nina events. This is an improvement from earlier coupled model simulations. In the model simulation, a modulation of the strength of the monsoon is due to a change of the large-scale land/ocean temperature gradient in the Indian Ocean sector in the mid-troposphere. The two composites show different developments during the annual cycle. In ENSO-related strong monsoon cases the atmosphere over land warms up during the spring in association with generally warmer tropics as a remnant from a warm event in the previous winter. During the summer months the warming in the Indian Ocean region is replaced by a cooling in association with the developing La Nina, while the land remains significantly warmer than normal. Therefore, in the coupled simulation the Indian Ocean only shows very small SST anomalies, while observed SSTs may vary in connection with ENSO events at a time lag of four months. Also for non-ENSO related monsoons a warming occurs over land in the summer, but then neither the Indian Ocean nor the tropical west Pacific exhibit any significant anomalies during the spring. Simulated temperature anomalies responsible for these modulations are relatively small. Independent of the origin of the monsoon anomaly, strong monsoons differ from weak monsoons by a significant precipitation pattern over Indian and a modification of the 850 hPa zonal wind field over the maritime continent and the West Pacific. Similar to observations, the anomalous monsoons in the coupled model are related to precursors in the 200 hPa zonal wind field in the spring, but no evidence could be found for a significant influence from the Eurasian snow pack in the spring on the subsequent Indian summer monsoon. While the model shows many realistic features, the variation of the monsoon occurs against a background of a deficient regional rainfall pattern in India and too small a range of Indian Ocean SST variations in conjunction with ENSO events.

Dugam, S. S., S. B. Kakade, et al. (1997). "Interannual and long-term variability in the North Atlantic Oscillation and Indian summer monsoon rainfall." Theoretical and Applied Climatology, Vienna, Austria 58(1-2): 21-29.

The interannual and decadal scale variability in the North Atlantic Oscillation (NAO) and its relationship with Indian Summer monsoon rainfall has been investigated using 108 years (1881-1988) of data. The analysis is carried out for two homogeneous regions in India, (Peninsular India and Northwest India) and the whole of India. The analysis reveals that the NAO of the preceding year in January has a statistically significant inverse relationship with the summer monsoon rainfall for the whole of India and Peninsular India, but not with the rainfall of Northwest India. The decadal scale analysis reveals that the NAO during winter (December-January-February) and spring (March-April-May) has a statistically significant inverse relationship with the summer monsoon rainfall of Northwest India, Peninsular India and the whole of India. The highest correlation is observed with the winter NAO. The NAO and Northwest India rainfall relationship is stronger than that for the Peninsular and whole of India rainfall on climatological and sub-climatological scales. Trend analysis of summer monsoon rainfall over the three regions has also been carried out. From the early 1930s the Peninsular India and whole of India rainfall show a significant decreasing trend (1% level) whereas the Northwest India rainfall shows an increasing trend from 1896 onwards. Interestingly, the NAO on both climatological and sub-climatological scales during winter, reveals periods of trends very similar to that of Northwest Indian summer monsoon rainfall but with opposite phases. The decadal scale variability in ridge position at 500 hPa over India in April at 75 degrees E (an important parameter used for the long-range forecast of monsoon) and NAO is also investigated.

Feng, X. (2001). "Interannual to Interdecadal Variation of East Asian Summer Monsoon and its Association with the Global Atmospheric Circulation and Sea Surface Temperature." Advances in Atmospheric Sciences 18(4): 567-575.

The East Asian summer monsoon (EASM) underwent an interdecadal variation with interannual variations during the period from 1958 to 1997, its index tended to decline from a higher stage in the mid-1960's until it reached a lower stage after 1980's. Correlation analysis reveals that EASM is closely related with the global atmospheric circulation and sea surface temperature (SST). The differences between the weak and strong stage of EASM shows that, the summer monsoon circulation over East Asia and North Africa is sharply weakened, in the meantime, the westerlies in high latitudes and the trade-wind over the tropical ocean are also changed significantly. Over the most regions south of the northern subtropics, both air temperature in the lower troposphere and SST tended to rise compared with the strong stage of EASM. It is also revealed that the ocean-atmosphere interaction over the western Pacific and Indian Ocean plays a key role in interannual to interdecadal variation of EASM, most probably, the subtropical Indian Ocean is more important. On the other hand, the ENSO event is less related to EASM at least during the concerned period.

Ferranti, L., J. M. Slingo, et al. (1997). "Relations between interannual and intraseasonal monsoon variability as diagnosed from AMIP integrations." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 123(541): 1323-1357.

Monsoon variability on intraseasonal and interannual time-scales is analysed using data from five 10-year European Centre for Medium-Range Weather Forecasts Atmospheric Model Intercomparison Project integrations, which differ only in their initial conditions. The results show that monsoon fluctuations within a season and within different years have a common dominant mode of variability. The spatial pattern of the common dominant mode in precipitation has a pronounced zonal structure, with one band of anomalous rainfall extending from 20 degrees N to 5 degrees N, covering most of the land areas, with the other band, of opposite sign, lying between 5 degrees N and 10 degrees S, mostly over the Indian Ocean. This mode therefore describes both the active/break monsoon spells associated with fluctuations of the Tropical Convergence Zone (TCZ) between the continental and the oceanic regime and the principal pattern of interannual variability of monsoon rainfall. In the observations the oscillations between active and break monsoon spells have similar behaviour, although the model is deficient in representing the rainfall variability over India. On the intraseasonal time-scale the transition between the two regimes seems to have a chaotic nature. In addition the probability density function of the principal mode is bimodal for the years in which this mode is particularly dominant. These two results indicate a possible similarity with the Lorenz 3-component chaotic model. Northward-propagating convective regions, simulated by the model, are not clearly associated with the phase transitions of the TCZ regime. The timing of the monsoon onset appears to be modulated by the phase of the El Nino/Southern Oscillation during the preceding season, consistent with observational studies. The results suggest that the dominant mode may also represent some components of the observed monsoon variability. The interannual fluctuations of the dominant mode exhibit only a weak level of reproducibility compared with the relatively large predictability of a broad-scale monsoon wind-shear index.

Fieux, M. (1985). "Observational strategy for TOGA in the tropical Indian Ocean." World Meteorological Organization, Geneva, WCRP Publications Series No(65).

As an introduction to the observational strategy for TOGA in the tropical Indian Ocean, the author presents current knowledge of the deep atmospheric convection in the eastern Indian Ocean, its linkage to high sea surface temperatures that affect convergence and the monsoon, the effect of the shift of the convective zone during an El Nino year, the SST variability as a response of the ocean to the variability of the large-scale atmospheric forcing, the highest seasonal variability of the tropical oceans characterizing the western Indian Ocean together with the Somali currents, the highly variable equatorial circulation peculiar to the Indian Ocean, the opposite features of the zonal thermoclines in the Indian Ocean and in the Pacific Ocean, the interannual variability superimposed on the seasonal variability, the association of the interannual variability with El Nino-Southern Oscillation in the Indian Ocean, and the evidence that the most pronounced anomalies of the thermocline are phase locked with the seasonal cycle. The large-scale monitoring network and the observational techniques required to understand the processes controlling SST changes and upper ocean content on intraseasonal, annual, and interannual time scales, and in particular, to determine the relative importance of advection, upwelling, surface fluxes, and heat storage, are described. The observational strategy of large-scale monitoring involves an internationally managed XBT program, a drifting buoys program, a direct sea level measurement program, satellite data collection and analysis, and a voluntary observing ship (VOS) program. Also, process-oriented studies are noted briefly.

Fink, A. (1995). "The physical causes for the variability of intraseasonal tropical convection fluctuations over the Indo-pacific." Koeln, Germany, Universitaet zu Koeln 118.

In the present study the role of variations in tropical sea surface temperature (SST) and atmospheric precipitable water as well as the phase of El Nino-Southern Oscillation (ENSO) for the interannual variability of the convective signal of the Madden-Julian-Oscillation (MJO) is investigated. Anomalous convective activity of MJO is estimated by the difference between the seasonal standard deviation of the 25-70 day filtered OLR and the long-term seasonal mean for the period 1974 through 1994. The respective roles of the forcing mechanisms mentioned above are considered for the year-to-year variability of both the seasonal anomalies of mean convection and the seasonal variations in convective activity associated with MJO-events. Interannual variability in tropical SST and the phase of ENSO are highly correlated with seasonal anomalies of mean convection as well as with seasonal anomalies of MJO-activity over the entire equatorial Pacific from 160 omicron E to the coast of South America. When SST occasionally exceeds 27 omicron C in the eastern equatorial Pacific and /or the climatological low-level divergence disappears in the central equatorial Pacific, the eastward propagating convective MJO-events are observed to penetrate farther into the central and eastern Pacific. This behaviour is typical for, but not exclusively observed during, El Nino seasons. Over the maritime continent deep convection is significantly supressed during El Nino years. A corresponding signal in the MJO-activity index is confined to the Philippine Sea and the Australian monsoon region during boreal winter. It is shown that the MJO-activity within the region of its climatological maximum, the eastern Indian Ocean, was below normal during El Nino winters 1976/77, 1982/83 and 1986/87. However, during the ENSO warm events 1991/1992 and 1993 MJO-activity was close to average over the eastern Indian Ocean. A different stratification of the five El Ninos with respect to anomalies in intraseasonal convection is obtained for the western Pacific warm pool. The atmospheric water vapor content is closly related to seasonal convection anomalies at most locations over the Indian and Pacific Ocean. The intensity of the high-frequency convective perturbations is also significantly correlated to seasonal anomalies in precipitable water. In contrast, convective activity of MJO shows no relation to variations in the amount of precipitable water. Since MJO is composed of a hierarchy of cloud clusters with time scales ranging from 1 to 14 days, which are found to be sensitive to the amount of precipitable water, it is concluded that the interannual variability of MJO over the Indian Ocean and western Pacific ,, warm pool[`] [`] is largely determined by its frequency of occurrence rather than by modulations of its amplitude. This is consistent with rather abrupt changes in periodicity of MJO, which can neither be related to changes in SST in the western Pacific warm pool nor to the phase of ENSO. An indication of a possible mechanism which is linked to the frequency of MJO-events is obtained from the statistically significant correlation between near-surface westerly wind anomalies and increased convective activity of MJO-events which is found in the western Pacific Ocean north of the equator. A possible connection between seasonal westerly wind anomalies and the occurrence of cold surges as a possible extratropical forcing mechanism of MJO is discussed.

Flatau, M., P. Flatau, et al. (1998). "Intraseasonal oscillations and Asian monsoon onset." Conference on the TOGA Coupled Ocean Atmosphere Response Experiment.

The Asian Summer Monsoon exhibits substantial interannual variability (?) which has profound social and economic consequences. This variability is intimately related to the phase of the El Nino /Southern Oscillation (ENSO) but also depends on the regional and intraseasonal behavior of the monsoon. In this paper we present the case of the multiple monsoon onset of 1995, triggered by the passage of the strong MJO episode in early May. The development the initial bogus onset was associated with a delay of the ``real'' onset and severe drought in India at the beginning of June. The delayed onset of monsoon in 1995 (Weller et al., 1998) was preceded by the development of circulation resembling summer monsoon in the middle of May with fairly strong south-westerly flow over Bay of Bengal and Arabian Sea, cross-equatorial flow east of Africa, pressure trough developing over Himalayas and convection in the northern Bay of Bengal. However, by late May, south-westerlies weakened, or even reverse, pressure trough filled and convection over Bay of Bengal disappeared. Monsoon condition started to develop again in early June in the south-eastern part of Bay of Bengal. The monsoon arrived at southern tip of India (the Kerala Coast) on June 8.

Fu, C. and J. O. Fletcher (1985). "Relationship between Tibet-tropical ocean thermal contrast and interannual variability of Indian monsoon rainfall." Journal of Climate and Applied Meteorology, Boston 24(8): 841-847.

During the northern summer, the Tibetan Plateau is a heat source for the atmosphere, and the Equatorial Pacific Ocean Cold Tongue is a heat sink, both contributing to the thermal forcing of large-scale quasi-zonal atmospheric circulation. For the period 1954-1979, interannual variability of Indian monsoon rainfall (I sub(M) ) is found to correlate highly with the thermal contrast between the Tibetan plateau (TP) and the equatorial cold tongue (ECT). An index of this thermal contrast (SLO for sea-land oscillation) is defined as the departure from the mean of the difference between the ground surface temperature of the Tibetan Plateau (T sub(s) ) and the surface temperature of the equatorial cold tongue (T sub(w) ). The interannual variability of T sub(s) and T sub(w) are of comparable magnitude and statistically independent of each other. The index of contrast (SLO) which contains them both correlates more strongly with Indian monsoon rainfall (0.61) than does either T sub(s) (0.30) or T sub(w) (0.52). The T sub(s) and T sub(w) each contribute approximately equally to the high correlation of SLO with I sub(M) . When the thermal contrast index (SLO) is strong (SLO > 0), it is a better indicator of Indian monsoon rainfall than when it is weak (SLO < 0).

Fu, C. and G. Wen (1999). "Variation of ecosystems over East Asia in association with seasonal, interannual and decadal monsoon climate variability." Climatic Change, Dordrecht, The Netherlands 43(2): 477-494.

Nearly half of the global low latitudes are characterized by a monsoon climate. This paper first analyzes the global spatial distribution of the rate of climate variation based on precipitation data. Results show that the monsoon regions in Asia and West Africa, and to a lesser extent in Australia, have the highest rate of climate variation on all time scales. These variations are manifested as seasonal jumps, high interannual and interdecadal variabilities, and abrupt changes between climate regimes. The monsoon regions are covered by various types of ecosystems which account for a large portion of the global biomass. Further analyses of the variations of ecosystems in the Asian region and their relationships with the monsoon climate have shown that the spatial and temporal variabilities of ecosystems are characterized by their strong response to variations in monsoon rainfall, one of the major energy flows in terrestrial ecosystems. The high rate of variation in monsoon climate strongly influences variation in Asian ecosystems. Changes in Asian ecosystems seem to be mainly driven by variations in monsoon climate over various time scales. This observation has led to the proposal of `monsoon-driven ecosystems' in Asia.

Fu, C. and D. Ye (1988). "The tropical very low-frequency oscillation on interannual scale." Advances in Atmospheric Sciences, Beijing, China 5(3): 369-388.

This is a review of the studies of tropical very low-frequency oscillation (VLFO) on an interannual scale, mainly on the recent research undertaken by Chinese scientists which is not well known outside of the country. This paper summarizes the basic features of VLFO in the tropics, the characteristic time and spatial structure of oscillation, especially the new concept of Low Latitude Oscillation which consists of two components: the well-known Southern Oscillation (SO) and the so-called Northern Oscillation (NO). A large volume of evidence has been provided to illustrate the relationship between VLFO in the tropics and the climate variation in China, such as the long-term variation of the north Pacific high, the frequency of typhoons and cyclones over the East China Sea, the summer monsoon rainfall in the Yangtze Valley basin and the cold summer disaster in northeast China, and so on. Finally, some light is thrown on the nature of VLFO on an interannual scale.

Fu, X. and B. Wang (1999). "The role of longwave radiation and boundary layer thermodynamics in forcing tropical surface winds." Journal of Climate, Boston, MA 12(4): 1049-1069.

This paper reveals major deficiencies of the existing intermediate climate models for tropical surface winds and elaborates the important roles of cloud-longwave radiational forcing and boundary layer thermodynamics in driving the tropical surface winds. The heat sink associated with the cloud-longwave radiation is demonstrated as an important driving force for boreal summer northeast trades and Indian Ocean southwest monsoons. Over the western North Pacific and Atlantic Oceans, low cloudiness and high sea surface temperature enhance longwave radiation cooling, strengthening subtropical high and associated trades. On the other hand, in the regions of heavy rainfall over South Asia, reduced cloud-longwave radiation cooling enhances monsoon trough and associated southwest monsoons. The boundary layer thermodynamic processes, primarily both the surface heat fluxes and the vertical temperature advection, are shown to be critical for a realistic simulation of the intertropical convergence zone, the equatorial surface winds, and associated divergence field. To successfully simulate the tropical surface winds, it is essential for intermediate models to adequately describe the feedback of the boundary layer frictional convergence to convective heat source, cloud-longwave radiation forcing, boundary layer temperature gradient forcing, and their interactions. The capability and limitations of the intermediate tropical climate model in reproducing both climatology and interannual variations are discussed.

Fujita, K., Y. Ageta, et al. (2000). "Mass balance of Xiao Dongkemadi glacier on the central Tibetan Plateau from 1989 to 1995." Annals of Glaciology, Cambridge, United Kingdom 31: 159-163.

Data on the mass balance of Xiao Dongkemadi glacier in the Tanggula mountains, central Tibetan Plateau, were obtained over 5.5 years from 1989 to 1995. These are the first continuous mass-balance data for a continental-type glacier on the Tibetan Plateau, where the glacier accumulates during the summer monsoon (summer-accumulation-type glacier). Mass-balance vs altitude profiles were steeper in the negative than in the positive mass-balance years. This is considered to have resulted from the effect of summer accumulation. The annual mass balance is compared with air temperature, precipitation, and black-body temperature in the area including the glacier, which is calculated from infrared radiation observations by the Japanese Geostationary Meteorological Satellite. It was found that the interannual variation in the glacier mass balance was not closely related to maximum monthly mean air temperature, while it did have a relatively good correlation with maximum monthly mean black-body temperature.

Gadgil, S. and S. Sajani (1998). "Monsoon precipitation in the AMIP runs." Climate Dynamics, Berlin, Germany 14(9): 659-689.

We present an analysis of the seasonal precipitation associated with the African, Indian and the Australian-Indonesian monsoon and the interannual variation of the Indian monsoon simulated by 30 atmospheric general circulation models undertaken as a special diagnostic subproject of the Atmospheric Model Intercomparison Project (AMIP). The seasonal migration of the major rainbelt observed over the African region, is reasonably well simulated by almost all the models. The Asia West Pacific region is more complex because of the presence of warm oceans equatorward of heated continents. Whereas some models simulate the observed seasonal migration of the primary rainbelt, in several others this rainbelt remains over the equatorial oceans in all seasons. Thus, the models fall into two distinct classes on the basis of the seasonal variation of the major rainbelt over the Asia West Pacific sector, the first (class I) are models with a realistic simulation of the seasonal migration and the major rainbelt over the continent in the boreal summer; and the second (class II) are models with a smaller amplitude of seasonal migration than observed. The mean rainfall pattern over the Indian region for July-August (the peak monsoon months) is even more complex because, in addition to the primary rainbelt over the Indian monsoon zone (the monsoon rainbelt) and the secondary one over the equatorial Indian ocean, another zone with significant rainfall occurs over the foothills of Himalayas just north of the monsoon zone. Eleven models simulate the monsoon rainbelt reasonably realistically. Of these, in the simulations of five belonging to class I, the monsoon rainbelt over India in the summer is a manifestation of the seasonal migration of the planetary scale system. However in those belonging to class II it is associated with a more localised system. In several models, the oceanic rainbelt dominates the continental one. On the whole, the skill in simulation of excess/deficit summer monsoon rainfall over the Indian region is found to be much larger for models of class I than II, particularly for the ENSO associated seasons. Thus, the classification based on seasonal mean patterns is found to be useful for interpreting the simulation of interannual variation. The mean rainfall pattern of models of class I is closer to the observed and has a higher pattern correlation coefficient than that of class II. This supports Sperber and Palmer's (1996) result of the association of better simulation of interannual variability with better simulation of the mean rainfall pattern. The hypothesis, that the skill of simulation of the interannual variation of the all-India monsoon rainfall in association with ENSO depends upon the skill of simulation of the seasonal variation over the Asia West Pacific sector, is supported by a case in which we have two versions of the model where NCEP1 is in class II and NCEP2 is in class I. The simulation of the interannual variation of the local response over the central Pacific as well as the all-India monsoon rainfall are good for NCEP2 and poor for NCEP1. Our results suggest that when the model climatology is reasonably close to observations, to achieve a realistic simulation of the interannual variation of all-India monsoon rainfall associated with ENSO, the focus should be on improvement of the simulation of the seasonal variation over the Asia West Pacific sector rather than further improvement of the simulation of the mean rainfall pattern over the Indian region.

Gadgil, S. and S. Sajani (1998). "Atmospheric Model Intercomparison Project (AMIP): monsoon precipitation in AMIP runs." Results from an AMIP diagnostic subproject, Geneva, Switzerland, World Meteorological Organization 28.

We present an analysis of the seasonal precipitation associated with the African, Indian and the Australian-Indonesian monsoon and the interannual variation of the Indian monsoon simulated by thirty atmospheric general circulation models undertaken as a special diagnostic subproject of the Atmospheric Model Intercomparison Project (AMIP). The seasonal migration of the major rainbelt observed over the African region, is reasonably well simulated by almost all the models. The Asia West Pacific region is more complex because of the presence of warm oceans equatorward of heated continents. Whereas some models simulate the observed seasonal migration of the primary rainbelt, in several others this rainbelt remains over the equatorial oceans in all the seasons. Thus the models fall into two distinct classes on the basis of the seasonal variation of the major rainbelt over the Asia West Pacific sector--the first (class 1) comprising models with a realistic simulation of the seasonal migration and the major rainbelt over the continent in the boreal summer; and the second (class II) comprising models with a smaller amplitude of seasonal migration than observed. The mean rainfall pattern over the Indian region for July-August (the peak monsoon months) is even more complex because, in addition to the primary rainbelt over the Indian monsoon zone (monsoon belt) and the secondary one over the equatorial Indian ocean, another zone with significant rainfall occurs over the foothills of Himalayas just north of the monsoon zone. Eleven models simulate the monsoon rainbelt reasonably realistically. Of these, in the simulations of five belonging to class I, the monsoon rainbelt over India in the summer is a manifestation of the seasonal migration of the planetary scale system, whereas in those belonging to class II it is associated with a more localized system. In several models, the oceanic rainbelt dominates the continental one. On the whole, the skill in simulation of excess /deficit summer monsoon rainfall over the Indian region is found to be much larger for models of class I than II, particularly for the ENSO associated seasons. Thus, the classification based on seasonal mean patterns is found to be useful for interpreting the simulation of interannual variation. The mean rainfall pattern of models of class I is closer to the observed and has a higher pattern correlation coefficience than that of class II supporting Sperber and Palmer's (1996) result of the association of better simulation of interannual variability with better simulation of the mean rainfall pattern. The hypothesis that the skill of simulation of the interannual variation of the all-India monsoon rainfall in association with ENSO depends upon the skill of simulation of the seasonal variation over the Asia West Pacific sector is supported by the one case in which we have two versions of the model viz. NCEP1 and NCEP2, with NCEP1 in class II and NCEP2 in class 1. The simulation of the interannual variation of the local response over the central Pacific as well as the all-India monsoon rainfall are good for NCEP2 and poor for NCEP1. Our results suggest that when the model climatology is reasonably close to observations, for achieving a realistic simulation of the interannual variation of all-India monsoon rainfall associated with ENSO, the focus should be on improvement of the simulation of the seasonal variation over the Asia West Pacific sector rather than further improvement of the simulation of the mean rainfall pattern over the Indian region.

Gagdil, S. (1988). "Recent advances in monsoon research with particular reference to the Indian monsoon." Australian Meteorological Magazine, Canberra 36(3): 193-204.

The major advances in the understanding of the structure of the Indian summer monsoon and its intraseasonal and interannual variations are discussed. The large-scale monsoon rainfall is shown to be associated with a tropical convergence zone (TCZ) having the dynamic characteristics of the ITCZ discussed by Charney (1969). The intraseasonal and interannual variations of the monsoon rainfall arise from the space-time variations of the TCZ. The prominent scales of intraseasonal variations between active spells and breaks are identified as the 15-day scale (associated with westward propagation of synoptic-scale disturbances) and the 40-day scale (associated with northward propagation of the TCZ). Detailed analysis of satellite imagery reveals that the most prominent feature of the intraseasonal variation over the Indian longitudes is the northward propagation of the TCZ from the equatorial Indian ocean onto the heated continent. So far such poleward propagations have not been reported for any other part of the Tropics. Simple models capable of simulating the seasonal transitions as well as the intraseasonal fluctuations of the monsoon have been developed; however, the underlying mechanisms are yet to be fully understood. The structure of the variations on the interannual scale is found to be markedly similar to that on the intraseasonal scale. Thus, analysis of the interrelationship of the continental TCZ with those over the Indian and the Pacific oceans on the intraseasonal scale, should provide insight into the interannual variations as well. On the interannual scale, links between the Asian monsoon and conditions over the Pacific as manifested by the association between the El Nino and Indian droughts have been well established. The relationship between SST and cloudiness over the tropics is shown to be rather complex, with a threshold of 28 degrees C for organized convection. With deeper understanding of the dynamics of the tropical convergence zones, more light is bound to be shed on the intraseasonal and interannual variations of the monsoon in the near future.

Garternicht, U. and F. Schott (1997). "Heat fluxes of the Indian Ocean from a global eddy-resolving model." Journal of Geophysical Research, Washington, DC 102(C9): 21147-21159.

The output of the global eddy-resolving 1/4 degrees ocean model of Semtner/Chervin (run by the Naval Postgraduate School, Monterey, California) has been used to study the oceanic temperature and heat flux in the Indian Ocean. The meridional heat flux in the northern Indian Ocean is at the low end of the observed values. A vertical overturning cell in the upper 500 m is the main contributor to the annual mean meridional heat flux across 5 degrees S, whereas the horizontal gyre circulation, confined to the upper 500 m, dominates north of the equator. The change of monsoon winds is manifested in a reversal of the meridional circulation throughout the whole water column. The most notable result is a strong linear relationship of the meridional temperature flux and the zonal wind stress component north of 20 degrees S. The model's Pacific-Indian Ocean throughflow across the section at 120 degrees E accounts for -8.8 plus or minus 5.1 Sv (1 Sv[idential] 10 super(6) m super(3) s super(-) super(1) ). A strong interannual variability during the model run of 3 years shows a maximum range of 12 Sv in January/February and a minimum during March through June. The inflow from the Pacific into the Indian Ocean results in a total annual mean temperature flux of -0.9 PW (1 PW[idential] 10 super(1) super(5) W). In the model the temperature flux from the Pacific through the Indian Ocean to the south dominates in comparison with the input of solar heat from the northern Indian Ocean.

Gautier, C., P. Peterson, et al. (1998). "Variability of air-sea interactions over the Indian Ocean derived from satellite observations." Journal of Climate, Boston, MA 11(8): 1859-1873.

Novel ways of monitoring the large-scale variability of the southwest monsoon in the Indian Ocean are presented using multispectral satellite datasets. The fields of sea surface temperature (SST), surface latent heat flux (LHF), net surface solar radiation (SW), precipitation (P), and SW-LHF over the Indian Ocean are analyzed to characterize the seasonal and interannual variability with special emphasis on the period 1988-90. It is shown that satellite data are able to make a significant contribution to the multiplatform strategy necessary to describe the large-scale spatial and temporal variability of air-sea interactions associated with the Indian Ocean Monsoon. The satellite data analyzed here has shown for the first time characteristics of the interannual variability of air-sea interactions over the entire Indian Ocean. Using monthly means of SST, LHF, SW, P, and the difference SW-LHF, the main features of the seasonal and interannual variability of air-sea interactions over the Indian Ocean are characterized. It is shown that the southwest monsoon strongly affects these interactions, inducing dramatic exchanges of heat between air and sea and large temporal variations of these exchanges over relatively small timescale (with regards to typical oceanic timescales). The analyses indicate an overall good agreement between satellite and in situ (ship) estimates, except in the southern Indian Ocean, where ship sampling is minimal, the disagreement can be large. In the latitudinal band of 10 degrees N-15 degrees S, differences in climatological in situ estimates of surface sensible heat flux and net longwave radiation has a larger influence on the net surface heat flux than the difference between satellite and in situ estimates of SW and LHF.

Giorgetta, M. A., L. Bengtsson, et al. (1999). "An investigation of QBO signals in the east Asian and Indian monsoon in GCM experiments." Climate Dynamics, Berlin, Germany 15(6): 435-450.

Observations have shown that the monsoon is a highly variable phenomenon of the tropical troposphere, which exhibits significant variance in the temporal range of two to three years. The reason for this specific interannual variability has not yet been identified unequivocally. Observational analyses have also shown that El Nino indices or western Pacific SSTs exhibit some power in the two to three year period range and therefore it was suggested that an ocean-atmosphere interaction could excite and support such a cycle. Similar mechanisms include land-surface-atmosphere interaction as a possible driving mechanism. A rather different explanation could be provided by a forcing mechanism based on the quasi-biennial oscillation of the zonal wind in the lower equatorial stratosphere (QBO). The QBO is a phenomenon driven by equatorial waves with periods of some days which are excited in the troposphere. Provided that the monsoon circulation reacts to the modulation of tropopause conditions as forced by the QBO, this could explain monsoon variability in the quasi-biennial window. The possibility of a QBO-driven monsoon variability is investigated in this study in a number of general circulation model experiments where the QBO is assimilated to externally controlled phase states. These experiments show that the boreal summer monsoon is significantly influenced by the QBO. A QBO westerly phase implies less precipitation in the western Pacific, but more in India, in agreement with observations. The austral summer monsoon is exposed to similar but weaker mechanisms and the precipitation does not change significantly.

Godfred-Spenning, C. R. and C. J. C. Reason (2002). "Interannual variability of lower-tropospheric moisture transport during the Australian monsoon." International Journal of Climatology 22(5): 509-532.

The interannual variability of the horizontal lower-tropospheric moisture transport associated with the Australian summer monsoon has been analysed for the 1958-99 period. The 41-season climatology of moisture flux integrated between the surface and 450 hPa showed moderate levels of westerly transport in the month before Australian monsoon onset, associated with cross-equatorial flow in the Sulawesi Sea and west of Borneo. In the month after onset the westerly moisture transport strengthened dramatically in a zonal belt stretching from the Timor Sea to the Western Equatorial Pacific, constrained between the latitudes 5 and 15 degree S, and associated with a poleward shift in the Intertropical Convergence Zone and deepening of the monsoon trough. Vertical cross-sections showed this transport extending from the surface to the 500 hPa level. In the second and third months after onset the horizontal flow pattern remained similar, although flux magnitudes progressively decreased, and the influence of trade winds became more pronounced over northern Australia. Nine El Nino and six La Nina seasons were identified from the data set, and composite plots of the affected years revealed distinct, and in some cases surprising, alterations to the large-scale moisture transport in the tropical Australian-Indonesian region. During an El Nino it was shown that the month prior to onset, in which the moisture flux was weaker than average, yielded to a dramatically stronger than average flux during the following month, with a zone of westerly flux anomalies stretching across the north Australian coast and Arafura Sea. The period of enhanced moisture flux during an El Nino is relatively short-lived, with drier easterly anomalies asserting themselves during the following 2 months, suggesting a shorter than usual monsoon period in north Australia. In the La Nina composite, the initial month after onset shows a tendency to weaker horizontal moisture transport over the Northern Territory and Western Australia. The subsequent 2 months show positive anomalies in flux magnitude over these areas; the overall effect is to prolong the monsoon. Comparison of these results with past research has led us to suggest that the tendency for stronger (weaker) circulations to arise in the initial month of El Nino (La Nina) events is a result of mesoscale changes in soil moisture anomalies on land and offshore sea surface temperature (SST) anomalies, brought about by the large-scale alterations to SST and circulation patterns during the El Nino-Southern Oscillation. The soil moisture and SST anomalies initially act to enhance (suppress) the conditions necessary for deep convection in the El Nino (La Nina) cases via changes in land-sea thermal contrast and cloud cover.

Goldenberg, S. B. and L. J. Shapiro (1996). "Physical mechanisms for the association of El Nino and West African rainfall with Atlantic major hurricane activity." Journal of Climate, Boston, MA 9(6): 1169-1187.

Physical mechanisms responsible for the contemporaneous association, shown in earlier studies, of North Atlantic basin major hurricane (MH) activity with western Sahelian monsoon rainfall and an equatorial eastern Pacific sea surface temperature index of El Nino are examined, using correlations with 200- and 700-mb level wind data for the period 1968-92. The use of partial correlations isolates some of the relationships associated with the various parameters. The results support previous suggestions that the upper- and lower-level winds over the region in the basin between similar to 10 degrees and 20 degrees N where most MHs begin developing are critical determinants of the MH activity in each hurricane season. In particular, interannual fluctuations in the winds that produce changes in the magnitude of vertical shear are one of the most important factors, with reduced shear being associated with increased activity and stronger shear with decreased activity. The results show that most of these critical wind fluctuations are explained by their relationship to the SST and rainfall fluctuations. Results confirm previous findings that positive (warm) eastern Pacific SST and negative (drought) Sahelian rainfall anomalies are associated with suppressed Atlantic basin tropical cyclone activity through an equatorially confined near-zonal circulation with upper-level westerlies and lower-level easterlies that act to increase the climatological westerly vertical shear in the main development region. SST and rainfall anomalies of the opposite sense are related to MH activity through a zonal circulation with upper-level easterly and lower-level westerly wind anomalies that act to cancel out some of the climatological westerly vertical shear. The results also show that changes in vertical shear to the north of the main development region are unrelated to, or possibly even out of phase with, changes in the development region, providing a possible physical explanation for the observations from recent studies of the out-of-phase relationship of interannual fluctuations in MH activity in the region poleward of similar to 25 degrees N with fluctuations in activity to the south. The interannual variability of MH activity explained by Sahel rainfall is almost three times that explained by the eastern Pacific SSTs. It is demonstrated that a likely reason for this result is that the SST-associated vertical shears are more equatorially confined, so that the changes in shear in the main development region have a stronger association with the rainfall than with the SSTs.

Goswami, B. N. (1998). "Interannual variations of Indian summer monsoon in a GCM: external conditions versus internal feedbacks." Journal of Climate, Boston, MA 11(4): 501-522.

The potential predictability of the Indian summer monsoon due to slowly varying sea surface temperature (SST) forcing is examined. Factors responsible for limiting the predictability are also investigated. Three multiyear simulations with the R30 version of the Geophysical Fluid Dynamics Laboratory's climate model are carried out for this purpose. The mean monsoon simulated by this model is realistic including the mean summer precipitation over the Indian continent. The interannual variability of the large-scale component of the monsoon such as the ``monsoon shear index'' and its teleconnection with Pacific SST is well simulated by the model in a 15-yr integration with observed SST as boundary condition. On regional scales, the skill in simulating the interannual variability of precipitation over the Indian continent by the model is rather modest and its simultaneous correlation with eastern Pacific SST is negative but poor as observed. The poor predictability of precipitation over the Indian region in the model is related to the fact that contribution to the interannual variability over this region due to slow SST variations [El Nino-Southern Oscillation (ENSO) related] is comparable to those due to regional-scale fluctuations unrelated to ENSO SST. The physical mechanism through which ENSO SST tend to produce reduction in precipitation over the Indian continent is also elucidated. A measure of internal variability of the model summer monsoon is obtained from a 20-yr integration of the same model with fixed annual cycle SST as boundary conditions but with predicted soil moisture and snow cover. A comparison of summer monsoon indexes between this run and the observed SST run shows that the internal oscillations can account for a large fraction of the simulated monsoon variability. The regional-scale oscillations in the observed SST run seems to arise from these internal oscillations. It is discovered that most of the interannual internal variability is due to an internal quasi-biennial oscillation (QBO) of the model atmosphere. Such a QBO is also found in the author's third 18-yr simulation in which fixed annual cycle of SST as well as soil moisture and snow cover are prescribed. This shows that the model QBO is not due to land-surface-atmosphere interaction. It is proposed that the model QBO arises due to an interaction between nonlinear intraseasonal oscillations and the annual cycle. Spatial structure of the QBO and its role in limiting the predictability of the Indian summer monsoon is discussed.

Goswami, B. N., V. Krishnamurthy, et al. (1999). "A broad-scale circulation index for the interannual variability of the Indian summer monsoon." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 125(554, Pt. B): 611-633.

A broad-scale circulation index representing the interannual variability of the Indian summer monsoon is proposed and is shown to be well correlated with the interannual variability of precipitation in the Indian monsoon region. Using monthly precipitation analysis based on merging rain-gauge data with satellite estimates of precipitation for the period 1979-96, it is shown that the variability of precipitation on seasonal to interannual time-scales is coherent over a large region covering the Indian continent as well as the north Bay of Bengal and parts of south China. A new index, termed Extended Indian Monsoon Rainfall (EIMR), is defined as the precipitation averaged over the region 70 degrees E-110 degrees E, 10 degrees N-30 degrees N. The EIMR index is expected to represent the convective heating fluctuations associated with the Indian monsoon better than the traditional all India Monsoon Rainfall (IMR) based only on the precipitation over the Indian continent. It is shown that large precipitation over the Bay of Bengal with significant interannual variability cannot be ignored in the definition of Indian summer monsoon and its variability. The June-to-September climatological mean EIMR is found to be larger than that of the IMR even though the former is averaged over a larger area. The dominant mode of interannual variability of the Indian summer monsoon is associated with a dipole between the EIMR region and the north-western Pacific region (110 degrees E-160 degrees E, 10 degrees N-30 degrees N) and a meridional dipole between the EIMR region and the equatorial Indian Ocean (70 degrees E-110 degrees E, 10 degrees S-5 degrees N). It is argued that the interannual variability of the monsoon circulation is primarily driven by gradients of diabatic heating associated with variations of the EIMR, and that the regional monsoon Hadley circulation is a manifestation of this heating. An index of the monsoon Hadley (MH) circulation is defined as the meridional wind-shear anomaly (between 850 hPa and 200 hPa) averaged over the same domain as the EIMR. Using circulation data from two independent reanalysis products, namely the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis and the European Centre for Medium-Range Weather Forecasts reanalysis, it is shown that the MH index is significantly correlated with the EIMR. Also it is shown that both the EIMR and MH indices have a dominant quasi-biennial variability, consistent with previous studies of IMR. Teleconnections of IMR, EIMR and MH indices with summer sea surface temperature (SST) have also been investigated. There are indications that the south equatorial Indian Ocean SST has a strong positive correlation with the EIMR. Also it is noted that the correlation of the monsoon indices with the eastern Pacific SST was weak during the period under consideration primarily due to almost a reverse relationship between monsoon and El Nino and Southern Oscillation during the latest eight years.

Goswami, B. N. and R. Mohan (2001). "Intraseasonal oscillations and interannual variability of the Indian summer monsoon." Journal of Climate, Boston, MA 14(6): 1180-1198.

How and to what extent the intraseasonal oscillations (ISOs) influence the seasonal mean and its interannual variability of the Indian summer monsoon is investigated using 42-yr (1956-97) daily circulation data from National Centers for Environmental Prediction-National Center for Atmospheric Research 40-Year Reanalysis and satellite-derived outgoing longwave radiation data for the period of 1974-97. Based on zonal winds at 850 hPa over the Bay of Bengal, a criterion is devised to define ``active'' and ``break'' monsoon conditions. The underlying spatial structure of a typical ISO cycle in circulation and convection that is invariant over the years is constructed using a composite technique. A typical ISO has large-scale horizontal structure similar to the seasonal mean and intensifies (weakens) the mean flow during its active (break) phase. A typical active (break) phase is also associated with enhanced (decreased) cyclonic low-level vorticity and convection and anomalous upward (downward) motion in the northern position of the tropical convergence zone (TCZ) and decreased (increased) convection and anomalous downward (upward) motion in the southern position of the TCZ. The cycle evolves with a northward propagation of the TCZ and convection from the southern to the northern position of the TCZ. It is shown that the intraseasonal and interannual variations are governed by a common mode of spatial variability. The spatial pattern of standard deviation of intraseasonal and interannual variability of low-level vorticity is shown to be similar. The spatial pattern of the dominant mode of ISO variability of the low-level winds is also shown to be similar to that of the interannual variability of the seasonal mean winds. The similarity between the spatial patterns of the two variabilities indicates that higher frequency of occurrence of active (break) conditions would result in ``stronger'' (``weaker'') than normal seasonal mean. This possibility is tested by calculating the two-dimensional probability density function (PDF) of the ISO activity in the low-level vorticity. The PDF estimates for ``strong'' and ``weak'' monsoon years are shown to be asymmetric in both the cases. It is seen that the strong (weak) monsoon years are associated with higher probability of occurrence of active (break) conditions. This result is further supported by the calculation of PDF of ISO activity from combined vorticity and outgoing longwave radiation. This clear signal indicates that the frequency of intraseasonal pattern determines the seasonal mean. Because the ISOs are essentially chaotic, it raises an important question on predictability of the Indian summer monsoon.

Goswami, B. N. and R. S. A. Mohan (2001). "Intraseasonal Oscillations and Interannual Variability of the Indian Summer Monsoon." Journal of Climate 14(6): 1180-1198.

How and to what extent the intraseasonal oscillations (ISOs) influence the seasonal mean and its interannual variability of the Indian summer monsoon is investigated using 42-yr (1956-97) daily circulation data from National Centers for Environmental Prediction-National Center for Atmospheric Research 40-Year Reanalysis and satellite-derived outgoing longwave radiation data for the period of 1974-97. Based on zonal winds at 850 hPa over the Bay of Bengal, a criterion is devised to define "active" and "break" monsoon conditions. The underlying spatial structure of a typical ISO cycle in circulation and convection that is invariant over the years is constructed using a composite technique. A typical ISO has large-scale horizontal structure similar to the seasonal mean and intensifies (weakens) the mean flow during its active (break) phase. A typical active (break) phase is also associated with enhanced (decreased) cyclonic low-level vorticity and convection and anomalous upward (downward) motion in the northern position of the tropical convergence zone (TCZ) and decreased (increased) convection and anomalous downward (upward) motion in the southern position of the TCZ. The cycle evolves with a northward propagation of the TCZ and convection from the southern to the northern position of the TCZ. It is shown that the intraseasonal and interannual variations are governed by a common mode of spatial variability. The spatial pattern of standard deviation of intraseasonal and interannual variability of low-level vorticity is shown to be similar. The spatial pattern of the dominant mode of ISO variability of the low-level winds is also shown to be similar to that of the interannual variability of the seasonal mean winds. The similarity between the spatial patterns of the two variabilities indicates that higher frequency of occurrence of active (break) conditions would result in "stronger" ("weaker") than normal seasonal mean. This possibility is tested by calculating the two-dimensional probability density function (PDF) of the ISO activity in the low-level vorticity. The PDF estimates for "strong" and "weak" monsoon years are shown to be asymmetric in both the cases. It is seen that the strong (weak) monsoon years are associated with higher probability of occurrence of active (break) conditions. This result is further supported by the calculation of PDF of ISO activity from combined vorticity and outgoing longwave radiation. This clear signal indicates that the frequency of intraseasonal pattern determines the seasonal mean. Because the ISOs are essentially chaotic, it raises an important question on predictability of the Indian summer monsoon.

Goswami, B. N., D. Sengupta, et al. (1998). "Intraseasonal oscillations and interannual variability of surface winds over the Indian monsoon region." Proceedings of the Indian Academy of Sciences, Bangalore, India 107(1): 45-64.

The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalyses for the period 1987-1996. Two dominant ISOs are found in all years, with a period between 30-60 days and 10-20 days respectively. Although the ISOs themselves explain only about 10-25% of the daily variance, the spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances), indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics of the two modes and their interannual variability are studied in detail. The synoptic structure of the 30-60 day mode is similar in all years and is shown to be intimately related to the strong (`active') or weak (`break') phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of Bengal corresponds to the `active' (`break') phase of monsoon strengthening (weakening) the entire large scale monsoon circulation. The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough). The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The vorticity pattern associated with the 30-60 day mode has a bi-modal meridional structure similar to the one associated with the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30-60 day mode is consistent with fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10-20 day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30-60 day mode. Elsewhere in the Indian Ocean, this mode is almost always weaker than the 30-60 day mode. In the Bay of Bengal region, the wind curl anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay. On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite structure of the 30-60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual scales.

Guo, Y. F., Y. Q. Yu, et al. (1996). "Mean climate state simulated by a coupled ocean-atmosphere general circulation model." Theoretical and Applied Climatology, Vienna, Austria 55(1-4): 99-111.

The result of a 100-year integration of a coupled ocean-atmosphere general circulation model (CGCM) is analyzed, and compared with that of a 25-year integration of the corresponding uncoupled atmospheric general circulation model (AGCM) and observed data. The large-scale circulation patterns of mean climate state simulated by the CGCM are in good agreement with the observed ones, although differences exist in the positions and intensities between the simulated and the observed patterns. Having compared the standard deviations of monthly mean sea level pressure simulated by the CGCM to those by the AGCM, we found that the interaction between ocean and atmosphere mainly increases the interannual variability in the tropics especially in summer. The CGCM can also produce El Nino and Southern Oscillation (ENSO) events, whereas the AGCM cannot reproduce the main features of the Southern Oscillation. This implies that the air-sea interaction may be a principal mechanism for the occurrence of ENSO phenomena. The fundamental features of simulated regional climates are also analyzed. The CGCM can reproduce principal characteristics of surface air temperature and precipitation at five selected typical regions (desert region, plain region, monsoon region etc.). The distributions of annual mean surface air temperature and precipitation in East Asia can also be reasonably simulated.

Hackert, E. C. and S. Hastenrath (1986). "Mechanisms of Java rainfall anomalies." Monthly Weather Review, Boston 114(4): 745-757.

The large-scale circulation departure patterns associated with the interannual variability of (July-June) rainfall in Java are studied on the basis of ship observations (1911-1973) in the Indian Ocean and surface station records. Circulation mechanisms of interannual variability can, in part, be understood as modulations of the average annual cycle. Abundant rainfall years are characterized by an anomalously strong northwest monsoon and, drought years, by approximately inverse circulation characteristics. In Dec.-Jan. of the wet years, anomalously high pressure near Southeast Asia along with anomalously low pressure over Indonesia entails an enhanced meridional pressure gradient, stronger northeasterly flow over the South China Sea and Bay of Bengal, and enhanced northwesterlies over the Indonesian waters. The increased northerly wind component to the north and intensified westerlies over the equatorial Indian Ocean result in enhanced convergence and cloudiness over Indonesia, whereas surface waters are cold. In May-Oct., anomalously low pressure, abundant cloudiness, and anomalous northwesterlies consistent with the enhanced pressure gradient are associated with a positive sea surface temperature anomaly in the Indonesian waters. By contrast, in Nov.-April, abundant cloudiness and anomalous northwesterlies associated with anomalously low pressure, but resulting in higher wind speed, accompany a negative sea surface temperature anomaly. Anomalously low pressure and warm surface waters in May-Oct. are followed by low pressure and low sea temperature in Nov.-April, which are succeeded by high May-Oct. pressure. This seasonally varying relationship among cloudiness, wind, and sea surface temperature appears instrumental for the functioning of the Southern Oscillation, inasmuch as a warm sea surface is conducive to an inflation of the atmospheric column and, thus, a rise of upper tropospheric constant pressure topographies and a drop of surface pressure, with the inverse effects ensuing from a negative sea surface temperature anomaly. This chain of causalities must be regarded as an essential part of the Southern Oscillation pressure seesaw between the Indonesian and eastern South Pacific dipoles. The memory of the combined atmosphere-ocean system presumably ensures the strong pressure persistence from the drier to the rainy half year, which provides a basis for climate prediction.

Halpern, D. and P. M. Woiceshyn (2001). "Somali Jet in the Arabian Sea, El Nino, India Rainfall." Journal of Climate 14(3): 434-441.

Interannual variations of the Somali Jet in the Arabian Sea during 1988-99 were linked to El Nino and La Nina episodes and to India west coast rainfall. Onset dates and monthly mean strengths of the Somali Jet were described with Special Sensor Microwave Imager surface wind speeds. Each year the Somali Jet formed in a similar area in the western Arabian Sea, and always before the onset of monsoon rainfall in Goa. The average date of Somali Jet onset was two days later in El Nino events in comparison with La Nina conditions. Monthly mean strength of the Somali Jet was 0.4 m s super(-1) weaker during El Nino episodes than during La Nina intervals. When the monthly mean intensity of the Somali Jet was above (below) normal, there was an excess (deficit) of rainfall along the Indian west coast.

Halpern, D. and P. M. Woiceshyn (2001). "Somali jet in the Arabian Sea, El Nino, and India rainfall." Journal of Climate, Boston, MA 14(3): 434-441.

Interannual variations of the Somali Jet in the Arabian Sea during 1988-99 were linked to El Nino and La Nina episodes and to India west coast rainfall. Onset dates and monthly mean strengths of the Somali Jet were described with Special Sensor Microwave Imager surface wind speeds. Each year the Somali Jet formed in a similar area in the western Arabian Sea, and always before the onset of monsoon rainfall in Goa. The average date of Somali Jet onset was two days later in El Nino events in comparison with La Nina conditions. Monthly mean strength of the Somali Jet was 0.4 m s super(-) super(1) weaker during El Nino episodes than during La Nina intervals. When the monthly mean intensity of the Somali Jet was above (below) normal, there was an excess (deficit) of rainfall along the Indian west coast.

Han, W. and P. J. Webster (2002). "Forcing Mechanisms of Sea Level Interannual Variability in the Bay of Bengal." Journal of Physical Oceanography 32(1): 216-239.

A nonlinear, 4 one half -layer reduced-gravity ocean model with active thermodynamics and mixed layer physics is used to investigate the causes of sea level interannual variability in the Bay of Bengal, which may contribute to flooding and cholera outbreaks in Bangladesh. Forcing by NCEP-NCAR reanalysis fields from 1958 to 1998 yields realistic solutions in the Indian Ocean basin north of 29 degree S. Controlled experiments elucidate the roles of the following forcing mechanisms: interannual variability of the Bay of Bengal wind, equatorial wind, river discharges into the bay, and surface buoyancy flux including precipitation minus evaporation (heat fluxes + P - E). Sea level changes in the bay result largely from wind variability, with a typical amplitude of 10 cm and occasionally 10-25 cm at an interannual timescale. Near the eastern and northern boundaries, sea level anomalies (SLAs) are predominantly caused by equatorial wind variability, which generates coastal Kelvin waves that propagate into the bay along the eastern boundary. Near the western boundary the bay wind has a comparable influence as the equatorial wind, especially during the southwest monsoon season, owing to the counterclockwise propagation of coastal Kelvin waves forced by the large-scale alongshore wind stress in the bay. In the bay interior, SLAs are dominated by the equatorial wind forcing in the central bay, result almost equally from the equatorial and the bay wind in the southwestern bay, and are dominated by the bay wind forcing in the southwestern bay during the southwest monsoon. The westward intensification of the bay wind influence is associated with the westward propagation of Rossby waves forced by the large-scale wind curl in the interior bay. The effect of heat fluxes + P - E is generally small. Influence of interannual variability of river discharges is negligible. SLAs caused by the equatorial wind at the equator and that caused by the bay wind along the northern and western boundaries as well as in the southwestern bay are significantly correlated, reflecting the anomalous wind pattern associated with the dipole mode event in the tropical Indian Ocean. Given the dominance of equatorial wind forcing near the northern bay boundary, SLAs (or alternatively westerly wind anomalies) in the equatorial ocean may serve as a potential index for predicting Bangladesh flooding and cholera.

Haque, M. A. and M. Lal (1991). "Space and time variability analyses of the Indian monsoon rainfall as inferred from satellite-derived OLR data." Climate Research, Amelinghausen, FRG 1(3): 187-197.

Five day mean Outgoing Longwave Radiation (OLR) data from June 1974 to May 1988 (14 yr period) derived from the NOAA polar satellite are analyzed to determine objectively the onset and withdrawal dates of the southwest monsoon over 7 selected regions of the Indian sub-continent and the adjoining seas. Monthly mean OLR anomalies are derived to examine the intra- as well as interannual variability of OLR distribution for each of the 7 regions. Linear correlation matrices are also constructed from standardized OLR anomalies to explain the spatial variability of OLR in individual years and to identify the statistical coherency between the regions in the years with excess, normal and deficient monsoon rainfall. Derived dates of the monsoon onset and withdrawal using OLR indices are in fair agreement with the dates of onset and withdrawal obtained based on the rainfall records. In general, the Indian sub-continent has a high positive OLR anomaly during the winter and pre-monsoon months and a moderate negative anomaly in the monsoon season. The distribution of OLR anomalies exhibits strong dependence on both temporal and spatial scales during the years with poor or excess monsoon rainfall.

Hastenrath, S. (1987). "Predictability of Java monsoon rainfall anomalies: a case study." Journal of Climate and Applied Meteorology, Boston 26(1): 133-141.

A substantial portion of the interannual variability of rainfall at Jakarta, Java, can be predicted from antecedent pressure anomalies at Darwin, northern Australia; the pressure persistence, the concurrent correlation of pressure and rainfall, and the predictability of rainfall from antecedent pressure are all largest during the east monsoon (June-Nov.). Because of the relatively simple large-scale circulation setting, warranting a single predictor (Darwin pressure), this region is chosen for a series of experiments aimed at exploring the seasonality and secular variations of predictability, optimal length of dependent record, and updating of the regression base period used for predictions on the independent data set. The major features of pressure-rainfall relationships are common through much of the 1911-1983 record, i.e., sign and general magnitude of correlations and the closer relationships during the east, as compared to the west, monsoon. Considerable differences are, however, apparent between decades. These may stem from both sampling deficiencies (noise) and real long-term changes of the pressure-rainfall couplings caused by secular alterations in the large-scale circulation setting. The competition between these two factors is relevant concerning the optimal length of the dependent record used for predictions into the independent data set, as well as the updating of the regression base period.

Hastenrath, S. (1987). "On the prediction of Indian monsoon rainfall anomalies." Journal of Climate and Applied Meteorology, Boston 26(7): 847-857.

A complex of anomalies in the premonsoon large-scale circulation setting heralds the interannual variability of India summer monsoon rainfall. The most prominent precursors of precipitation anomalies are the latitude position of the upper air ridge over India, apparently reflecting the persistence of the boreal winter wind regime and its consequence for the establishment of the summer upper air circulation; the temperature in southern Asia and the adjacent North Indian Ocean waters, a factor instrumental in heat-low development and, hence, the establishment of meridional pressure gradients and lower tropospheric air streams from the Southern Hemisphere; and indices of the Southern Oscillation, capturing pressure departure patterns spanning the global Tropics. Stepwise multiple regression is used to extract from this anomaly complex the variance most pertinent to the interannual variability of Southwest monsoon rainfall, with observations of pertinent elements being available for the period 1939-1981. Regression models developed on a portion of this record are then used to predict the summer monsoon rainfall anomalies of the years 1966-1981. The correlations between the various precursors and the rainfall anomalies vary in the course of 1939-1981, and are, on the whole, strongest in the 1950s and 1960s. While the April latitude position of the 500-mb ridge along 75 degrees E proves to be the strongest predictor, performance is improved by inclusion of other elements representing preseason temperature and the Southern Oscillation. Correlation, root mean square error, bias, and absolute error are used as measures of forecast performance. A set of experiments with the dependent data set, ending in 1965, indicates that a regression base period of similar to 20 yr is optimal for predictions into the independent portion of the record. Another set of experiments, in which the regression base periods are successively updated to the year immediately preceding the year to be forecast, shows no improvement of predictions over the fixed regression base periods. Cross validation is not found less demanding than prediction proper. It is demonstrated that approximately one-half of the interannual variance in monsoon rainfall can be predicted from antecedent anomalies in the large-scale circulation setting.

Hastenrath, S. (1990). "The relationship of highly reflective clouds to tropical climate anomalies." Journal of Climate, Boston, MA 3(3): 353-365.

The interannual variability of tropical convection related to the Southern Oscillation (SO) and regional climate anomalies is studied from satellite-derived estimates of highly reflective clouds (HRC) during 1971-87. The novel HRC data bank provides a particularly useful measure of tropical convection for the purposes of climate diagnostics, because of its length and continuity of record. For the first time, maps are presented of the patterns of correlation between the SO, as well as regional rainfall anomalies, and convection over the global tropics. Throughout the year, the SO (high SO phase defined by anomalously high/low pressure at Tahiti /Darwin) exhibits a highly significant negative correlation with HRC in the equatorial Pacific but a much weaker positive correlation with Indonesia. The SO is correlated positively with HRC in the Amazon basin in boreal winter but negatively with HRC over central Africa throughout most of the year. The three equatorial convection centers tend to vary in unison, in particular those over the Amazon basin and central Africa, while the positive correlations of any of these centers with the SO are much weaker. Copious precipitation during the March-April rainy season of northeast Brazil is associated with a southward displaced low-pressure trough and embedded wind confluence, as well as a southward shift of the convection belt in the sector extending from South America across the Atlantic into equatorial Africa. During abundant Nordeste rainy seasons, as in the high SO phase, convective activity tends to be enhanced over Indonesia but reduced in the equatorial Pacific. Copious rainfall in Subsaharan West Africa (Sahel) tends to be associated with the high SO phase and thus intense convection over Indonesia and reduced convective activity in the equatorial central Pacific. Another new finding is the strong inverse relationship of Sahel rainfall with the convection over central Africa. Abundant Indian summer monsoon rainfall is accompanied by enhanced convective activity over the Indian Ocean and Indonesia and reduced convection in the equatorial central Pacific, characteristics of the high SO phase.

Hattemer-Frey, H. A., T. R. Karl, et al. (1986). "Annotated inventory of climatic indices and data sets." United States. Dept. of Energy, Office of Energy Research, Office of Basic Energy Sciences, Wash., D.C., DOE/NBB 0080(195).

This publication describes 34 prominent climatic indices and provides an annotated listing and bibliography of additional indices to meet the information needs of researchers who are evaluating the effects of increased CO sub(2) levels. The indices are grouped into 10 subject areas: 1) global/hemispheric data sets (monitoring a climatic variable for one or both hemispheres): Northern Hemisphere surface air temperature, Russian surface air temperatures, and Southern Hemisphere surface air temperatures; 2) marine data sets: comprehensive ocean-atmosphere data sets (COADS), global sea level changes, nighttime near-surface marine air temperatures, and tide-gage measurement of global sea level changes; 3) global and local long-term temperature and precipitation data sets: Arctic, Arctic regions, and Antarctic surface air temperatures; central England temperatures; dryness/wetness index for China; England, and Wales precipitation; Indian monsoon rainfall record and drought area indices; New Zealand temperature and precipitation record; rainfall series for four sub-Saharan zones; sub-Saharan rainfall index; and U.S. temperature and precipitation record and drought area index; 4) atmospheric constituents data sets: aircraft measurements of atmospheric CO sub(2) concentrations over the Australian region; atmospheric CO sub(2) variations at Mauna Loa Observatory, Hawaii, and the South Pole; dust veil index; and mean annual stratospheric aerosol optical depths estimates; 5) upper air data sets: circulation patterns and world climate, trade wind field over the Pacific Ocean, and tropospheric and stratospheric temperatures; 6) Southern Oscillation/El Nino data sets: atmospheric characteristics associated with the Southern Oscillation, persistence and interannual variability of the Southern Oscillation, and Southern Oscillation indices; 7) solar data sets: umbra/penumbra ratio, and Zurich (Wolf) sun-spot numbers; 8) Proxy data sets: 22-yr cycle in drought area indices for the western U.S.; past volcanic activity determined from Greenland ice cores; reconstructed estimates of temperature, sea level pressure, and Southern Oscillation index values; and reconstructed Northern Hemisphere temperatures; 9) lake level and river flow data sets: changes in the level of three East African lakes; and 10) snow cover and sea ice extent data sets: changes in snow cover and sea ice and the reflection loss index for the Northern Hemisphere. Additional climatic indices are listed in the appendix; and an extensive bibliography is included. For each of the 34 climatic indices, the following information is given: the primary reference, the application, the background, the calculation, the temporal and spatial resolutions, the units, the period of record, the reliability, the manner in which the index compares with other indices, the sponsor of the index, and the number of times the primary reference has been cited since published.

He, Y., C. Guan, et al. (1997). "Interannual and interdecadal variations in heat content of the upper ocean of the South China Sea." Advances in Atmospheric Sciences, Beijing, China 14(2): 271-276.

The vertically averaged temperature (TAV) from surface to 100 m depth of the South China Sea for the period 1959-1988 is analyzed. The results indicate that there is a significant long-term variability from interannual to interdecadal scales in the heat content in the upper ocean. The heat content of the upper ocean of the South China Sea increases evidently in the El Nino year. TAV anomaly in the ocean was negative from the end of 1950's to early 1970's, and then changed to positive. The changes of TAV of the ocean are closely related to ENSO events, the Asian winter monsoon and the tropical atmospheric circulation anomalies.

Hennessy, K. J., R. Suppiah, et al. (1999). "Australian rainfall changes, 1910-1995." Australian Meteorological Magazine, Canberra, Australia 48(1): 1-13.

Annual and seasonal trends in heavy daily rainfall, total rainfall and the number of rain days were calculated for the whole of Australia and each State/Territory from 1910 to 1995, using high-quality daily data from 379 stations. Trend significance was determined using the Kendall-tau test and trend magnitudes were computed from linear regression. While many statistically significant trends were found, non-significant trends judged to be of special interest are noted. From 1910-1995, annual total rainfall has undergone secular changes with a significant 14 per cent increase in Victoria and non-significant increases of 15-18 per cent in New South Wales (NSW), the Northern Territory (NT) and South Australia (SA). When analysed seasonally, non-significant changes of 10-40 per cent were found in some States. Heavy rainfall indices were defined as the 99th and 95th percentiles (the highest and 5th highest daily amounts, respectively, in each three-month season). Australian areal-mean heavy rainfall has not changed significantly in any season. However, on a regional basis significant increases in heavy rainfall emerged in SA in summer and NSW in autumn, while significant decreases occurred in southwest Western Australia (SWWA) in winter. Important non-significant increases of 10-45 per cent were also found in some States. There has been a significant 10 per cent rise in the annual Australian-average number of rain days. Significant increases of almost 20 per cent were found in the NT and NSW despite a significant 10 per cent decline in SWWA. Regionally, significant increases of 20-50 per cent have occurred in some States, with large changes in the frequency of light rainfall. Strong correlations exist between interannual variations in temperature, total rainfall, heavy rainfall and the number of rain days. Increases in Australian rainfall since 1910 are generally linked to an increase in heavy rainfall and the number of rain days. ENSO variability is partly responsible, as is enhanced monsoon activity in the 1970s and changes in other large-scale circulation features. Decreased rainfall in southwest WA is also linked to circulation changes.

Hewitt, C. D. and J. F. B. Mitchell (1996). "GCM simulations of the climate of 6 kyr BP: mean changes and interdecadal variability." Journal of Climate, Boston, MA 9(12, Pt. III): 3505-3529.

A simulation of the climate for 6 kyr BP, using the Hadley Centre's atmospheric GCM with prescribed SSTs is described. The control simulation successfully reproduces the large-scale features of the present-day climate and has realistic atmospheric interannual variability. The anomaly simulation for 6 kyr BP produces a climate with an enhanced Northern Hemisphere seasonal cycle, and, in particular, a strengthened African-Asian summer monsoon. Integrated over the full annual cycle, the land surface of the southern Tropics dries while the northern Tropics get wetter, and the high northern latitudes also dry. The model simulates large regional interdecadal differences in the response at 6 kyr BP highlighting the need to allow for and account for variability on long, that is, at least decadal, timescales. The authors describe the consequences of part of the experimental design employed, whereby the SSTs for the 6 kyr BP simulation are the same as in the control as recommended by the Paleoclimate Modelling Intercomparison Project, in particular, the potential importance of ocean and sea ice feedbacks.

Higgins, R. W., K. C. Mo, et al. (1998). "Interannual variability of the U.S. summer precipitation regime with emphasis on the southwestern monsoon." Journal of Climate, Boston, MA 11(10): 2582-2606.

Relationships between the interannual variability of the U.S. summer precipitation regime and the intensification, weakening, or changes in position of the climatological-mean circulation features that organize this regime are examined. The focus is on the atmospheric conditions over the conterminous United States relative to wet and dry monsoons over the southwestern United States. The onset of the monsoon in this region, which typically begins in early July, is determined using an index based on daily observed precipitation for a 32-yr (1963-94) period. Composites of observed precipitation and various fields from the National Centers for Environmental Prediction-National Center for Atmospheric Research Reanalysis for wet and dry monsoons are used to show that the interannual variability of the summer precipitation regime closely mimics the seasonal changes associated with the development of the North American monsoon system. The warm season precipitation regime is characterized by a continental-scale precipitation pattern consisting of an out-of-phase relationship between the Southwest and the Great Plains/Northern Tier and an in-phase relationship between the Southwest and the East Coast. This pattern is preserved for both wet and dry monsoons, but the Southwest is relatively wetter and the Great Plains are relatively drier during wet monsoons. Wet (dry) monsoons are also associated with a stronger (weaker) upper-tropospheric monsoon anticyclone over the western United States, consistent with changes in the upper-tropospheric divergence, midtropospheric vertical motion, and precipitation patterns. The intensity of the monsoon anticyclone over the western United States appears to be one of the most fundamental controls on summertime precipitation downstream over the Great Plains. Evidence is presented that the interannual variability of the U.S. warm season precipitation regime is linked to the season-to-reason ``memory'' of the coupled atmosphere-ocean system over the eastern tropical Pacific. In particular, it is shown that SST anomalies in the eastern Pacific cold tongue and precipitation anomalies in the intertropical convergence zone, present during the winter and spring preceding the monsoon, are linked via an anomalous local Hadley circulation to the warm season precipitation regime over the United States and Mexico. Wet (dry) summer monsoons tend to follow winters characterized by dry (wet) conditions in the Southwest and wet (dry) conditions in the Pacific Northwest. This association is attributed, in part, to the memory imparted to the atmosphere by the accompanying Pacific SST anomalies.

Higgins, R. W. and W. Shi (2000). "Dominant factors responsible for interannual variability of the summer monsoon in the southwestern United States." Journal of Climate, Boston, MA 13(4): 759-776.

Interannual variability of the summer monsoon in the southwestern United States is controlled by various ocean-and land-based conditions (e.g., SST, soil moisture, and snow cover) that provide sources of memory of antecedent climate anomalies such as ENSO. It is hypothesized that this interannual variability is also modulated by decade-scale fluctuations in the North Pacific SSTs. The following observations have been made in support of this hypothesis. First, the summer precipitation regime is dominated by a continental-scale precipitation pattern characterized by an out-of-phase relationship between precipitation in the southwestern United States and that in the Great Plains of the United States. Second, interannual fluctuations in the onset date of the monsoon in the southwestern United States are significantly correlated with interannual fluctuations in the intensity of summer rainfall in this region such that early monsoons are often very wet and late monsoons tend to be dry. Third, wet (dry) monsoons in the southwestern United States often follow winters characterized by dry (wet) conditions in the southwestern United States and wet (dry) conditions in the northwestern United States. Finally, interannual variability of the summer monsoon in the southwestern United States is modulated by long-term (decade scale) fluctuations in the North Pacific SSTs. The mechanism relating the North Pacific SST pattern to interannual variability in the summer monsoon appears to be via the impact of variations in the Pacific jet on West Coast precipitation regimes during the preceding winter. Multiyear fluctuations in the North Pacific SST pattern are consistent with multiyear fluctuations in the atmospheric circulation and in the West Coast precipitation regimes during Northern Hemisphere (NH) winter, hence with multiyear variability in the summer monsoon state. Influences on the summer monsoon during the preceding winter and spring are tied together using appropriate SST indices that capture decade-scale variability in the North Pacific during NH winter and interannual variability in the eastern tropical Pacific during NH spring. The results suggest that decadal variability in the North Pacific SSTs may be an important factor in determining long-term periods of summertime drought or rainy conditions in the southwestern United States and in the Great Plains of the United States.

Higgins, R. W. and W. Shi (2001). "Intercomparison of the Principal Modes of Interannual and Intraseasonal Variability of the North American Monsoon System." Journal of Climate 14(3): 403-417.

Time series of seasonal-, monthly, and pentad-mean precipitation are subjected to empirical orthogonal function analysis, regression analysis, and compositing techniques to study the principal modes of interannual and intraseasonal variability of the North American Monsoon System (NAMS). The leading principal component (PC) from the summertime seasonal-mean data is associated with El Nino-Southern Oscillation (ENSO) variability while the leading PC from the pentad-mean data is associated with 30-60-day intraseasonal (Madden-Julian) oscillations (MJOs). The leading PC from the monthly mean data is a hybrid of the two above-mentioned modes, capturing aspects of both. The leading PCs are used as reference time series for regressions and composites that reveal the structure of the principal modes and their manifestation in the NAMS. The leading PCs are also used to estimate the fraction of the variance of summer precipitation that is explained by ENSO and by interannual variations of MJO activity. ENSO-related impacts on the NAMS are linked to meridional adjustments of the ITCZ. In its positive polarity, the leading PC of interannual variability is associated with warm (ENSO) episodes and is characterized by an expansion of the ITCZ toward the south, increased precipitation in a zonally oriented band just north of the equator, and decreased precipitation over Mexico and portions of the Caribbean. MJO-related impacts on the NAMS are linked to more regional meridional adjustments in the precipitation pattern over the eastern tropical Pacific. In its positive polarity, the leading PC of intraseasonal variability is associated with an intensification and northward adjustment of the precipitation pattern in the eastern tropical Pacific, with increased precipitation over the warm pool to the west of Mexico and over portions of Mexico and the southwestern United States. Both the interannual and intraseasonal modes have well-defined, but distinct, sea level pressure and surface wind signatures in the eastern tropical Pacific. These features extend to the middle troposphere and are capped by circulation features in the opposite sense in the upper troposphere. The relationship of the MJO to the NAMS is examined in more detail using the leading PC of intraseasonal variability and an objective procedure to identify the phase of MJO events. The leading PC is strongly related to the eastward progression of centers of enhanced (reduced) convection around the global Tropics on intraseasonal timescales. Notably, a strong relationship between the leading mode of intraseasonal variability of the NAMS, the MJO, and the points of origin of tropical cyclones in the Pacific and Atlantic basins is also present.

Higgins, R. W. and W. Shi (2001). "Intercomparison of the principal modes of interannual and intraseasonal variability of the North American Monsoon System." Journal of Climate, Boston, MA 14(3): 403-417.

Time series of seasonal-, monthly, and pentad-mean precipitation are subjected to empirical orthogonal function analysis, regression analysis, and compositing techniques to study the principal modes of interannual and intraseasonal variability of the North American Monsoon System (NAMS). The leading principal component (PC) from the summertime seasonal-mean data is associated with El Nino-Southern Oscillation (ENSO) variability while the leading PC from the pentad-mean data is associated with 30-60-day intraseasonal (Madden-Julian) oscillations (MJOs). The leading PC from the monthly mean data is a hybrid of the two above-mentioned modes, capturing aspects of both. The leading PCs are used as reference time series for regressions and composites that reveal the structure of the principal modes and their manifestation in the NAMS. The leading PCs are also used to estimate the fraction of the variance of summer precipitation that is explained by ENSO and by interannual variations of MJO activity. ENSO-related impacts on the NAMS are linked to meridional adjustments of the ITCZ. In its positive polarity, the leading PC of interannual variability is associated with warm (ENSO) episodes and is characterized by an expansion of the ITCZ toward the south, increased precipitation in a zonally oriented band just north of the equator, and decreased precipitation over Mexico and portions of the Caribbean. MJO-related impacts on the NAMS are linked to more regional meridional adjustments in the precipitation pattern over the eastern tropical Pacific. In its positive polarity, the leading PC of intraseasonal variability is associated with an intensification and northward adjustment of the precipitation pattern in the eastern tropical Pacific, with increased precipitation over the warm pool to the west of Mexico and over portions of Mexico and the southwestern United States. Both the interannual and intraseasonal modes have well-defined, but distinct, sea level pressure and surface wind signatures in the eastern tropical Pacific. These features extend to the middle troposphere and are capped by circulation features in the opposite sense in the upper troposphere. The relationship of the MJO to the NAMS is examined in more detail using the leading PC of intraseasonal variability and an objective procedure to identify the phase of MJO events. The leading PC is strongly related to the eastward progression of centers of enhanced (reduced) convection around the global Tropics on intraseasonal timescales. Notably, a strong relationship between the leading mode of intraseasonal variability of the NAMS, the MJO, and the points of origin of tropical cyclones in the Pacific and Atlantic basins is also present.

Hoerling, M. P., T. K. Schaack, et al. (1990). "Heating distributions from January and July simulations of NCAR community climate models." Journal of Climate, Boston, MA 3(4): 417-434.

Simulations of the global distribution of heating (the sum of latent, sensible, short and longwave radiation) are presented for January and July using the R15 NCAR Community Climate Model (CCM). The vertical and horizontal distributions of heating predicted by an earlier version of the CCM (CCM0B) are contrasted with those predicted by the current version of the CCM (CCM1) in which substantial revisions were made in the physical parameterizations of convective, radiative, and sensible heating. The results are compared with climatological studies of atmospheric heating and with recent diagnostic analyses of heating during the Global Weather Experiment (GWE). The dominant heat sources in the CCM simulations of January and July are located over Indonesia-Southeast Asia in broad agreement with the primary feature of the observed Asian monsoon; however, several marked distinctions between the vertically averaged heating distributions for CCM0B and CCM1 occur. During January, centers of maximum heating are located farther south of the equator in CCM1 than in CCM0B. This southward shift in CCM1 is accompanied by strong heating along the South Pacific and South Atlantic convergence zones. These latter features are largely absent in CCM0B. Additionally, CCM1 heating over the monsoon regions of southern Africa and South America is nearly double that found in CCM0B. Similarly, during July, CCM1 heating in the monsoon regions of northern Africa, the western Pacific, and Central America is nearly double that observed in CCM0B. With fixed boundary conditions (e.g., sea surface temperatures, soil moisture, sea ice extent, and snow cover) in the perpetual simulations, the interannual variability of heating is due entirely to internal model dynamics. The interannual variability of both January and July heating is larger in CCM1 than in CCM0B. Regions of maximum interannual variability in both CCM0B and CCM1 are found in the vicinity of the principal tropical heat source regions. This variability is associated primarily with in situ fluctuations in the intensity of regional heating centers, while geographical displacements appear to be of secondary importance. Major differences are found between the vertical distributions of heating for CCM0B and CCM1. These stem largely from changes in physical parameterizations, in particular a change in the prescribed critical relative humidity for condensation by moist stable and unstable adiabatic adjustment from 80% in CCM0B to 100% in CCM1, and a replacement of dry convective adjustment in CCM0B by vertical diffusion of heat and moisture in CCM1. In the tropics, maximum heating occurs in the lower troposphere in CCM0B, while strongest heating occurs in the mid- to upper troposphere in CCM1. In the storm tracks of extratropical latitudes, heating is confined below 800 mb in CCM0B, while heating of appreciable magnitude extends above 500 mb in CCM1. The vertical distribution of heating in CCM1 agrees favorably with diagnosed distributions for the GWE, while the CCM0B heating distribution does not.

Holland, G. J. (1986). "Interannual variability of the Australian summer monsoon at Darwin: 1952-82." Monthly Weather Review, Boston 114(3): 594-604.

Fluctuations in the Australian summer monsoon over the period 1952-1982 are described. The basis of the study is an objective definition of the major summer monsoon components based on the low-level zonal winds at Darwin; this is shown to be in good agreement with other large-scale indicators. Statistics are presented and discussed for the interannual variation in summer monsoon onset, extent, active and break conditions, circulation strength, and vertical structure. Some relationships with the Southern Oscillation are also described. These indicate that the Southern Oscillation Index (SOI) is highly correlated with the intensity and degree of convergence in the low-level monsoonal shear zone and with the mean daily rainfall rate over northern Australia. There is also a significant correlation between the summer monsoon onset date and the SOI in the following spring, which has implications for El Nino teleconnections.

Hsu, H. H., Y. L. Chen, et al. (2001). "Effects of atmosphere ocean interaction on the interannual variability of winter temperature in Taiwan and East Asia." Climate Dynamics 17(4): 305-316.

This study investigated the ocean-atmosphere interaction effect on the winter surface air temperature in Taiwan. Temperature fluctuations in Taiwan and marine East Asia correlated better with a SST dipole in the western North Pacific than the SST in the central/eastern equatorial Pacific. During the warm (cold) winters, a positive (negative) SST anomaly appears in marine East Asia and a negative (positive) SST anomaly appears in the Philippine Sea. The corresponding low-level atmospheric circulation is a cyclonic (anticyclonic) anomaly over the East Asian continent and an anticyclonic (cyclonic) circulation in the Philippine Sea during the warm (cold) winters. Based on the results of both numerical and empirical studies, it is proposed that a vigorous ocean-atmosphere interaction occurring in the western North Pacific modulates the strength of the East Asian winter monsoon and the winter temperature in marine East Asia. The mechanism is described as follows. The near-surface circulation anomalies, which are forced by the local SST anomaly, strengthen (weaken) the northeasterly trade winds in the Philippine Sea and weaken (strengthen) the northeasterly winter monsoon in East Asia during warm (cold) winters. The anomalous circulation causes the SST to fluctuate by modulating the heat flux at the ocean surface. The SST anomaly in turn enhances the anomalous circulation. Such an ocean-atmosphere interaction results in the rapid development of the anomalous circulation in the western North Pacific and the anomalous winter temperature in marine East Asia. This interaction is phase-locked with the seasonal cycle and occurs most efficiently in the boreal winters.

Hu, Q. (2002). "Interannual Rainfall Variations in the North American Summer Monsoon Region: 1900-98." Journal of Climate 15(10): 1189-1202.

The following questions are addressed in this study using an array of data and statistical methods: 1) does the North American monsoon region have a single dominant monsoon system; 2) if it has more than one, what are they; and 3) what are major causes of interannual monsoon rainfall variations in these systems? Results showed two dominant summer monsoon systems in the region: one in south-central Mexico, south of the 26 'N, and the other in the southwestern United States and northwestern Mexico. Monsoon rainfall variations in these regions are usually opposite to each other and have different causes. The interannual variations in monsoon rainfall in south-central Mexico were highly affected by interannual variations in the intertropical convergence zone (ITCZ) in the eastern tropical Pacific. A northern (southern) position of the ITCZ, often related to cooler (warmer) than normal sea surface temperatures in the eastern tropical Pacific Ocean, corresponded to strong (weak) monsoon. The 'land memory effect' was evident in interannual variations of monsoon rainfall in the southwestern United States, shown by strong correlations of the summer rainfall variation versus antecedent winter precipitation anomalies in the western United States. However, the effect was not robust but varied fairly regularly. It was strong from approximately 1920 to 1930 and disappeared from 1931 to 1960. It regained its strength from 1961 to 1990 but has weakened again since 1990. The forcing of this variation was identified as a multidecadal variation in atmosphere circulations in the North Pacific-North American sector and the land memory effect was part of this variation. This multidecadal variation has to be included in prediction methods in order for them to correctly describe seasonal and interannual variations in summer rainfall in the North American monsoon region.

Huang, J. and Q. Zhu (1996). "MLCB low-frequency wind in flood/drought years and its interannual difference." Journal of Nanjing Institute of Meteorology, Nanjing, China 19(3): 276-282.

Based on the low-frequency windfields, study is made of the difference in low-frequency oscillation (LFO) between flood- and drought-hit years and the relation to rainfall. Results suggest that in such years the low-frequency component makes up greatly varying portion for the circulation systems in east China and the MLCB (mid-lower Changjiang basins) rainfall-related wind features and variation are quite distinct; in 1980 as the flood year over the MLCB the change in precipitation is closely associated with the LFO in the East-Asian monsoon region, especially in subtropical monsoon, with its northward propagation in a phatic manner, marked by a quasi-8 pentad period, thus responsible for the periodic variation in rainfall whilst in 1988 as the year of drought the rainfall change bears no relation to East-Asian monsoon's LFO but to a vigorous low-frequency vortex dominating the northern portion of East Asia, which originates from the one over the waters east of Japan moving north and then turning west, and the movement and development are at a quasi-8 pentad period, too, leading to change in rainfall over the MLCB.

Huijun, W., X. Feng, et al. (2002). "The Spring Monsoon in South China and Its Relationship to Large-Scale Circulation Features." Advances in Atmospheric Sciences 19(4): 651-664.

In this paper, the authors define the spring monsoon in South China, and study the climatology and the interannual variation through analysis of the precipitation and the related atmospheric circulation, as revealed by the NCEP/NCAR reanalysis data. The results indicate that the spring monsoon season in South China occurs climatologically in April and May, which is supported by both seasonal and interannual variation of the atmospheric circulation and precipitation. The related atmospheric circulation is different from that during the East Asian summer or winter monsoon season. The interannual variation of the spring monsoon rainfall in South China relates primarily to the anomalous circulation over the North Pacific, which is linked with the westerly jet over North Asia and with the polar vortex. It is also connected with sea surface temperature anomalies in the Pacific. Changes in the Asian tropical atmospheric circulation has little influence on the spring monsoon in South China according to this research.

Hwang, C. and S.-A. Chen (2000). "Fourier and wavelet analyses of TOPEX/POSEIDON-derived sea level anomaly over the South China Sea: a contribution to the South China Sea Monsoon Experiment." Journal of Geophysical Research, Washington, DC 105(C12): 28785-28804.

We processed 5.6 years of TOPEX/Poseidon altimeter data and obtained time series of sea level anomaly (SLA) over the South China Sea (SCS). Fourier analysis shows that sea level variability of the SCS contains major components with periods larger than 180 days and is dominated by the annual and semiannual components. Tidal aliasing creates 30-180 day components that can be misinterpreted as wind-induced variabilities. Continuous and multiresolution wavelet analyses show that the SLA of the SCS has monthly to interannual components of time-varying amplitudes, and the regional slope of SLA is 8.9 mm yr super(-) super(1) , which may be caused by the decadal climate change. Coherences of SLA with wind stress anomalies (WSA) and sea surface temperature anomalies (STA) are significant at the annual and semi-annual components. At periods of 2-5 years the wavelet coefficients of SLA, WSA, and STA have the same pattern, but WSA leads SLA, and STA follows SLA. The zero crossing of SLA in spring is highly correlated with the onset of the summer monsoon. The interannual variability of SLA is correlated with El Nino-Southern Oscillation, and most important is that when the El Nino-like wavelet coefficients of SLA over the warm pool northeast of Australia or the SCS change curvature from negative to positive, an El Nino is likely to develop. This is a contribution to the South China Sea Monsoon Experiment (SCSMEX).

Iyengar, R. N. (1991). "Application of principal component analysis to understand variability of rainfall." Proceedings of the Indian Academy of Sciences Earth and Planetary Sciences, Bangalore, India 100(2): 105-126.

This paper presents the usefulness of principal component analysis for understanding the temporal variability of monsoon rainfall. Monthly rainfall data of Karnataka, collected from 50 stations for a period of 82 years have been analysed for interseasonal and interannual variabilities. A subset of the above data comprising 10 stations from the coherent west zone of Karnataka has also been investigated to bring out statistically significant interannual signals in the southwest monsoon rainfall. Conditional probabilities are proposed for a few above normal/below normal transitions. A sample prediction exercise for June-July using such a transition probability has been found to be successful.

Iyengar, R. N. and P. Basak (1994). "Regionalization of Indian monsoon rainfall and long-term variability signals." International Journal of Climatology, New York, NY 14(10): 1095-1114.

Large regions in India with homogeneous variability of monsoon rainfall are identified with the help of principal component analysis. Four major regions, called principal regions, are first demarcated. Even though the variance explained by the first PC is only 21 per cent, it can be used to organize 45 per cent of the surface area into a coherent region. A novel sequential methodology wherein at every step the grouped stations are sieved out is also proposed. This helps in identifying 10 sequentially homogeneous regions accounting for 91 per cent of the total area under consideration. The four principal regional rainfall series reflect the interannual variability originally present in the data set. These are mutually uncorrelated and hence represent four independent monsoon anomaly patterns also. The first and the fourth principal regions contain temporal signals well discriminated from white noise.

Jacobi, C. (2000). "Midlatitude mesosphere/lower thermosphere region winds and their connection with European and Asian tropospheric parameters." Theoretical and Applied Climatology, Vienna, Austria 65(3-4): 231-243.

Investigation of long-term measurements of winter mesosphere/lower thermosphere (MLT) region zonal winds has shown a connection of Northern Hemisphere tropospheric parameters and MLT conditions. These are on one hand due to a connection of the stratospheric polar vortex and the North Atlantic Oscillation (NAO) and on the other hand forced by a coupling of the troposphere/lower stratosphere and the MLT region through planetary wave propagation and wave-mean flow interaction. The connection between European and Asian winter climatological parameters and the NAO leads to the fact, that the signal of Eurasian winter conditions can be found in the interannual variability of MLT winds. Some of these winter tropospheric parameters influence the strength of the Indian monsoon in the following summer, and this leads to a correlation between winter MLT winds and summer Indian rainfall, so that the midlatitude MLT winter dynamics can be used as a precursory signal of the strength of the Indian monsoon.

Janicot, S., S. Trzaska, et al. (2001). "Summer Sahel-ENSO teleconnection and decadal time scale SST variations." Climate Dynamics 18(3/4): 303-320.

The correlation between Sahel rainfall and El Nino-Southern Oscillation (ENSO) in the northern summer has been varying for the last fifty years. We propose that the existence of periods of weak or strong relationship could result from an interaction with the global decadal scale sea surface temperature (SST) background. The main modes of SST variability have been extracted through a principal component analysis with Varimax rotation. The correlations between a July-September Sahel rainfall index and these SST modes have been computed on a 20-year running window between 1945 and 1993. The correlations with the interannual ENSO-SST mode are negative, not significant in the 1960s during the transition period from the wet climate phases to the long-running drought in the Sahel, but then were significant since 1976. During the former period, the correlations between the Sahel rainfall index and the other SST modes (expressing mostly on quasi and multi-decadal scales) are the highest, in particular correlations with the tropical Atlantic "dipole. Correlations between Sahel and Guinea Coast rainfall are also significantly negative. After 1970, the Sahel-Guinea Coast rainfall correlations are no longer significant, and the ENSO-SST mode becomes the only one significantly correlated with Sahel rainfall, especially due to the impact of warm events. The partial correlations between the ENSO-SST mode and the Sahel rainfall index, when the influence of the other SST modes are eliminated, are significant over all the 20-year running periods between 1945 and 1993, suggesting that this summer teleconnection could be modulated by the decadal scale SST background. The NCEP/NCAR reanalyses reproduce accurately the interannual variability of the atmospheric circulation after 1968. In particular a regional West African Monsoon Index (WAMI), combining wind speed anomalies at 925 and 200 hPa, is highly correlated with the July-September Sahel rainfall index. A warm ENSO event is associated both with an eastward mean sea level pressure gradient between the eastern tropical Pacific and the tropical Atlantic and with a northward pressure gradient along the western coast of West Africa. This pattern leads to enhanced trade winds over the tropical Atlantic and to weaker moisture advection over West Africa, consistent with a weaker monsoon system strength and a weaker Southern Hemisphere Hadley circulation.

Ji, L., S. Sun, et al. (1997). "Model study on the interannual variability of Asian winter monsoon and its influence." Advances in Atmospheric Sciences, Beijing, China 14(1): 1-22.

The interannual variation of Asian winter (NE) monsoon and its influence is studied using the long-term integration of Max-Plank Institute ECHAM3 (T42 L19) model. The simulation well reproduces the main features of the climatological mean Asian winter monsoon and shows pronounced difference of atmospheric circulation between strong and weak winter monsoon and for the consecutive seasons to follow. Most striking is the appearance and persistence of an anomalous cyclonic flow over the western Pacific and enhanced Walker circulation for strong winter monsoon in agreement with the observation. The contrast in summer rainfall patterns of both East China and India can also be discerned in the simulation. Comparison of three sets of experiments with different SST shows that the forcing from the anomalies of global SST makes a major contribution to the interannual variability of Asian winter monsoon and, in particular, to the interseasonal persistence of the salient features of circulation. The SSTA over the tropical western Pacific also plays an important part of its own in modulating the Walker circulation and the extratropical flow patterns. The apparent effect of strong NE monsoon is to enhance the convection over the tropical western Pacific. This effect, on the one hand, leads to a strengthening of SE trades to the east and extra westerly flow to the west, thus favorable to maintaining a specific pattern of SSTA. On the other hand, the thermal forcing associated with the SSTA acts to strengthen the extratropical flow pattern which is, in turn, conductive to stronger monsoon activity. The result seems to suggest a certain self-sustained regime in the air-sea system, which is characterized by two related interactions, namely the air-sea and tropical-extratropical interactions with intermittent outburst of NE cold surge as linkage. There is a connection between the strength of the Asian winter monsoon and the precipitation over China in the following summer. Links between these two variabilities are mainly through SST anomalies but snow over Asia is a contributing factor as well.

Jinhai, H., Z. Bing, et al. (2001). "Vertical Circulation Structure, Interannual Variation Features and Variation Mechanism of Western Pacific Subtropical High." Advances in Atmospheric Sciences 18(4): 497-510.

The paper investigates the vertical circulation structure of the western Pacific subtropical high (STH) and its interannual variation features in relation to East Asian subtropical summer monsoon and external thermal forcing by using the high-resolution and good-quality observations from the 1998 South China Sea Summer Monsoon Experiment (SCSMEX), the NCEP 40-year reanalysis data and relevant SST and the STH parameters. It is found that the vertical circulation structures differ greatly in features between quasi-stationary and transient components of the western Pacific STH. When rainstorms happen in the rainband of East Asian subtropical monsoon on the STH north side, the downdrafts are distinct around the ridge at a related meridian. The sinking at high (low) levels comes from the north (south) side of the STH, thereby revealing that the high is a tie between tropical and extratropical systems. The analyses of this paper suggest that the latent heat release associated with subtropical monsoon precipitation, the offshore SST and East Asian land-sea thermal contrast have a significant effect on the STH interannual anomaly. Our numerical experiment shows that the offshore SSTA-caused sensible heating may excite an anomalous anticyclonic circulation on the west side, which affects the intensity (area) and meridional position of the western Pacific STH.

Joseph, P. V., J. K. Eischeid, et al. (1994). "Interannual variability of the onset of the Indian summer monsoon and its association with atmospheric features, El Nino, and sea surface temperature anomalies." Journal of Climate, Boston, MA 7(1): 81-105.

The long-term mean date of the monsoon onset over Kerala (MOK) varies between 30 May and 2 June according to different estimates, with a standard deviation of 8-9 days. The earliest date of MOK, and the most delayed one, during the last 100 years differ by 46 days (7 May and 22 June, respectively). MOK switches on a spatially large and intense convective heat source over south Asia, lasting from June to September, whose moisture supply is made available through the cross-equatorial low-level jet stream. Superposed epoch analysis of 10 years of outgoing longwave radiation (OLR) data shows that MOK is a significant stage in the evolution of the OLR field in the tropics of the eastern hemisphere. At the time of MOK there is increased convection in a band about 5-10 degrees wide meridionally, extending from the south Arabian Sea to south China, and convection is suppressed all around, particularly in the western Pacific Ocean. In 1983 when MOK was delayed by about 3 pentads, OLR data showed that the boreal spring-to-summer migration of the equatorial convective cloudiness maximum (ECCM), both westward and northward, was also delayed. The delayed MOK is accompanied by delays in the northwestward movement of ECCM and is confirmed by an analysis of long-term data of southwest Pacific tropical cyclones. Of the 22 years between 1870-1989 when MOK was delayed by 8 days or more, 16 cases were associated with a moderate or strong El Nino. Of the 13 strong El Ninos during the same period, 9 were associated with moderate-to-large delays in MOK. Delays preferentially occurred in the year+1 of an El Nino, where year 0 is the growing phase of the El Nino in sea surface temperature (SST). Analysis of the SST field has shown that delayed MOK is associated with warm SST anomalies at and south of the equator in the Indian and Pacific oceans and cold SST anomalies in the tropical and subtropical oceans to the north during the season prior to the monsoon onset (i.e., March to May). It is hypothesized that such SST anomalies over the Indian and Pacific oceans (generally found associated with El Nino, either in year 0 or year+1 or in both) cause the interannual variability of the MOK through their action in affecting the timing of the northwestward movement of the ECCM.

Joseph, P. V., B. Liebmann, et al. (1991). "Interannual variability of the Australian summer monsoon onset: possible influence of Indian summer monsoon and El Nino." Journal of Climate, Boston, MA 4(5): 529-538.

The date of Australian summer monsoon onset (ASMO) is found to be well correlated with the monsoon rainfall of India during the preceding June to September. Years of below (above) normal Indian summer monsoon rainfall (ISMR) are followed by delayed (early) ASMO. Sea surface temperature (SST) anomalies during the September to November season over the tropical Indian Ocean, the equatorial eastern Pacific Ocean, and the ocean north of Australia also correlate significantly with the date of the following ASMO. Delays in ASMO are associated with cold SST north of Australia and warm SST in the tropical Indian and equatorial east Pacific oceans. Previous studies have shown that a warm SST is created over the tropical Indian Ocean in years of poor ISMR. We hypothesize that a warm SST anomaly over the Indian Ocean delays the seasonal southward and eastward migration of the cloudiness maximum. A delay in the southeastward movement of cloudiness results in a delayed ASMO. A similar hypothesis already has been suggested to explain the variability of the date of monsoon onset over India. Weak ISMR often is associated with the contemporaneous presence of El Nino, although many weak monsoons occur without El Nino. Thus warm SSTs in the eastern equatorial Pacific are related to a delayed ASMO through the Indian monsoon. Another signature of El Nino is the presence of negative SST anomalies north of Australia, adding to the delay in ASMO. Warm SSTs in the central and eastern Pacific may also act directly to delay ASMO by causing convection near and east of the date line and subsidence near Australia.

Joseph, P. V. and P. V. Pillai (1984). "Air-sea interaction on a seasonal scale over [the] north Indian Ocean, Pt. 1, Interannual variations of sea surface temperature and Indian summer monsoon rainfall." Mausam, New Delhi 35(3): 323-330.

Monthly mean sea surface temperatures (SST) obtained from ship observations have been studied for two selected representative areas (SRA) in the Arabian Sea and one in the Bay of Bengal for the 13-yr period 1961 to 1973. Each SRA is 3 degrees long. x 2 degrees lat. They are centered, A at 11 degrees 00'N, 59 degrees 30'E; B at 14 degrees 00'N, 71 degrees 30'E; and C at 11 degrees 00'N, 83 degrees 30'E. Twelve monthly running means of the monthly mean SST of each SRA show a pronounced 3-yr oscillation during the whole period. The series of monthly anomalies of SST for A, B, and C were subjected to harmonic and power spectrum analyses, which also show that, apart from the annual variation, the only prominent periodicity is the 3-yr variation. For the 9-yr period 1965-1973, 5 degrees -square averages of monthly mean SST have been worked out for the Indian Ocean area north to 15 degrees S. It is found that the 3-yr oscillation in SST covers a large area of the northern Indian Ocean, where power spectrum analysis of SST monthly anomalies shows significant peaks at a 95% confidence level for this oscillation. Correlations between monsoon rainfall of India and the SST anomalies at A, B, and C have been worked out by using data of 1961-1973. It is found that the SST of premonsoon months is positively correlated with the following monsoon rainfall, but the correlation is low and not statistically significant. However, the monsoon rainfall is significantly negatively correlated with the postmonsoon SST of areas A, B, and C.

Ju, J. and J. Slingo (1995). "The Asian summer monsoon and ENSO." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 121(525, Pt. A): 1133-1168.

The relationship between the evolution of the Asian summer monsoon and equatorial sea-surface-temperature anomalies has been studied using results from an integration with the UK Universities' Global Atmospheric Modelling Programme (UGAMP) General Circulation Model (UGCM). The integration was performed as part of the Atmospheric Model Intercomparison Project and thus used the observed sea surface temperatures (SSTs) for the decade January 1979 to December 1988. The mean evolution of the Asian summer monsoon has been successfully simulated in terms of many aspects of the rapid transition of the large-scale circulation during the boreal spring and summer. However, the results for individual years showed considerable interannual variability, both in the strength of the monsoon and in the time of onset. A relationship has been identified between the evolution of the monsoon flow and the phase of the El Nino Southern Oscillation (ENSO). In agreement with observed results, years with warm SST anomalies in the equatorial central and east Pacific Ocean (El Nino) have a weaker monsoon circulation and a delayed onset. An opposite behaviour is noted for those years with cold Pacific SST anomalies (La Nina). Diagnostics from analyses from the National Meteorological Center and the European Centre for Medium-range Weather Forecasts, and from data on the outgoing long-wave radiation observed by the Advanced Very High Resolution Radiometer, have been used to verify the model results. A description of the mechanism by which the phase of ENSO remotely influences the dynamics of the Asian summer monsoon has been developed involving changes in the heating patterns over Indonesia and the west Pacific in the preceeding spring.

Jury, M. R. (1996). "Regional teleconnection patterns associated with summer rainfall over South Africa, Namibia and Zimbabwe." International Journal of Climatology, Chichester, UK 16(2): 135-153.

Climatic determinants of southern African summer rainfall are analysed using statistical techniques. Summer rainfall time series are formulated for South Africa, Namibia and Zimbabwe areas and correlated with global indices and with field variables: sea-surface temperature (SST), outgoing longwave radiation (OLR), and tropospheric winds at 200 and 700 hPa levels. Linear regression correlations are performed using monthly standardized departures at various lags before and during the summer season. The SSTs in the central equatorial Indian Ocean (CEI) are identified as significant predictors/modulators of southern African rainfall. The SSTs at the CEI are best correlated with South Africa rainfall at r<-0[small solid circle] 6 at lags -2 and 0 months and are associated with the El Nino. The SSTs of the CEI modulate the overlying monsoon trough, as indicated by the OLR correlation maps. A centre of convective action alternates between southern Africa and the southwest Indian Ocean from year-to-year. A useful circulation index that emerges in the statistical analysis is springtime zonal upper wind anomalies over the equatorial central Atlantic. This index is correlated with South Africa rainfall at r<-0[small solid circle] 8 at lags -4 and -2 months. Westerly (easterly) 200 hPa anomalies in spring are followed by a summer of below (above) normal rainfall. Other patterns that have a bearing on summer rainfall include a circulation gyre identified in 700 hPa wind correlations off the coast of southeast Africa. This circulation feature controls the flux of moisture between southern Africa and the northern Mozambique Channel. The correlation patterns offer statistical guidance in long-range forecasts and insights to climatic processes that govern the interannual variability of summer rainfall over southern Africa.

Jury, M. R., B. A. parker, et al. (1995). "Variability of summer rainfall over Madagascar: climatic determinants at interannual scales." International Journal of Climatology, Chichester, UK 15(12): 1323-1332.

Variability of convective rainfall in the austral summer season over central Madagascar is studied using an area-rainfall index, local radiosonde data, and gridded information on outgoing longwave radiation (OLR), sea-surface temperature, and tropospheric winds. Seasonal rainfall patterns are influenced by topography, monsoon and trade wind circulations, and tropical cyclone events. The Inter Tropical Convergence Zone overlies the north-west coast, where summer rainfall averages 47 cm month super(-) super(1) . Climatic conditions that affect convective rainfall at interannual time-scales are studied through spatial lag correlation analysis. Sea-surface temperature is weakly correlated with rainfall departures, with positive values in the central Indian Ocean reaching +041 at lags -4 and 0 months. Strongest positive correlations (+0.45) gradually shift to the central South Atlantic Ocean at lag 0 and +2 months. Wind correlations imply that increased upper level tropical easterly flow overlying enhanced low-level north-west monsoon flow favours above normal rainfall. Regional teleconnection patterns identified by rainfall-OLR correlations are remarkably similar to those for Quasi-biennial oscillation (QBO)-OLR correlations, suggesting that up to one-third of the interannual convective variance can be explained by the phase of the QBO.

Jury, M. R., B. Pathack, et al. (1999). "Climatic determinants and statistical prediction of tropical cyclone days in the southwest Indian Ocean." Journal of Climate, Boston, MA 12(6): 1738-1746.

Climatic determinants of tropical cyclone (TC) days in the southwest Indian Ocean area (10 degrees -25 degrees S, 50 degrees -70 degrees E) are analyzed using statistical techniques. A TC days index is formulated from records of local meteorological services over the December-March season in the period 1961-91. The index is correlated with gridded fields of sea surface temperature (SST), outgoing longwave radiation (OLR), and tropospheric winds, using monthly standardized departures at various lags. SST relationships with TC days are positive over the entire southwest Indian Ocean from -4 to +2 months, as expected. Peak correlations of >+0.5 occur in the genesis region 0 degrees -10 degrees S, 50 degrees -60 degrees E to the northeast of Madagascar at lag -4 (September). The synoptic-scale response of monsoon convection is approximated by OLR correlations. Negative correlations (associated with increased convection) are found to the northeast of Madagascar at lag -4 and 0 months. At lags -4 and -2 (November) opposing positive OLR correlations are found over Africa, suggesting a convective sink region during the spring season transition. Wind correlation vectors at the 200-hPa level indicate the persistence of an anticyclonic gyre centered near 35 degrees S, 70 degrees E in the south Indian Ocean and upper easterly flow in the equatorial zone. Surface northwesterly flow is a prominent feature in the central Indian Ocean (Diego Garcia), while strengthened midlatitude westerlies are found at lag -4 (September). In November surface northwesterly flow anomalies dominate the entire tropical zone with respect to summers with increased TC days. At lag 0 and to a lesser extent +2 months, a distinct cyclonic anomaly is centered on 20 degrees S, 55 degrees E with enhanced monsoon westerlies to the north. The correlation patterns offer statistical guidance in long-range forecasts and insights to the climatic processes involved in the interannual variability of TC days in the southwest Indian Ocean. Using predictors selected from present analysis, a linear multivariate model is constructed. The model has three predictors from the preceding July to November period and accounts for 59% of the variance over the 1971-92 period. The model performs adequately, achieving a jackknife correlation of 70% and a Heidke tercile score of 52.5%. A conceptual framework is used to highlight relationships between the predictors, the Indian monsoon, and tropical cyclogenesis.

Kane, R. P. (1995). "Quasi-biennial and quasi-triennial oscillations in the summer monsoon rainfall of the meteorological subdivisions of India." Monthly Weather Review, Boston, MA 123(4): 1178-1184.

The summer monsoon rainfall time series for 29 subdivisions of India from 1951 to 1991 (41 years) were subjected to maximum entropy spectral analysis and showed significant periodicities in a wide range, including quasi-biennial oscillation (QBO 2-3 years) and quasi-triennial oscillation (QTO 3-3.9 years). After filtering out periodicities of 4.0 years or more, the residual series, considered as representative of QBO and QTO only for each series, could be separated into 4 categories (viz., category A of 10 subdivisions having only one strong QBO peak but no QTO, category B of 4 subdivisions having two strong QBO peaks but no QTO, category C of 4 subdivisions having no strong QBO or QTO, and category D of 11 subdivisions having a strong QTO). The 50-mb zonal wind showed two strong QBO peaks at 2.33 years (28 m) and 2.75 years (33 m). A comparison of stratospheric (50 mb) westerly wind and rainfall maxima showed that for many subdivisions, maximum rainfall was associated with the increasing westerly phase of zonal wind and droughts were associated with the easterly phase. A loose relationship with El Nino-Southern Oscillation was also noticed for droughts in some subdivisions (mostly western India), and the two effects (50-mb wind and ENSO) seem to be operating independently of each other.

Kar, S. C., M. Sugi, et al. (1996). "Simulation of the Indian summer monsoon and its variability using the JMA global model." Papers in Meteorology and Geophysics, Ibaraki, Japan 47(2): 65-101.

Ten-year integrations of the JMA global model at T106 and T42 horizontal resolutions were compared to examine the role of model resolution in simulating the Indian monsoon and its variability. It has been found that both T106 and T42 models simulate mean monsoon climatology reasonably well in terms of the large-scale monsoon flow. The T106 model simulates rainfall distribution in western and northwestern parts of India better than the T42 model. Correlation of interannual variability (IAV) of simulated rainfall with observed IAV is poor. The simulated IAVs of the Indian monsoon rainfall for both models do not have a strong correlation with the SST, either. The T42 model simulated the rainfall variability for 1987/88 better than the T106 model. Monsoon rainfall variability may be largely due to internal dynamics in both models. Internally generated variability may be larger in T106 model than T42 model simulations. Rainfall anomaly patterns obtained from T42 model simulations are better than those of T106 model simulations for the two pairs of good and bad monsoon events (1988/87 and 1983/82). Responses of both the coarser and finer resolution models to the same imposed surface forcing differ over the Indian monsoon region. Both models simulate the synoptic evolution of the monsoon quite well. Monsoon activity in the T106 model is more intense than in the T42 model. Rainfall distribution is better obtained from T106 model simulations than T42 model simulations. This suggests that further work is necessary in relating intraseasonal variations with interannual monsoon variability for understanding the nature of monsoon variability.

Karoly, D. J. and D. G. Vincent (1998). "Meteorology of the Southern Hemisphere." Boston, MA, American Meteorological Society 410.

A comprehensive description of the meteorology of the Southern Hemisphere was originally provided in the monograph of the same title published by the American Meteorological Society in 1972. That monograph was, of necessity, preliminary in nature because the available time series of observational data was short. In the quarter century that has passed since the first monograph, much has happened to warrant an updated edition: new observational techniques based on satellites, anchored and drifting buoys, and more ground-based stations have expanded the observational network to cover the whole hemisphere. The time is right, therefore, for a fresh look at the circulation features of the Southern Hemisphere, which is provided in this monograph, both for the atmosphere and oceans. The present monograph deals in greater detail with regional climates and updates the knowledge of circulation features such as the Australian monsoon; the South Pacific convergence zone; the South Atlantic convergence zone; the subtropical and polar jet streams, cyclones, and storm tracks; and the circulation in the stratosphere. These topics are dealt with mainly in the first four chapters and in chapter 6. Subjects that were not mentioned in the previous monograph are found in the remaining five chapters. They include mesoscale circulations; stratospheric ozone depletion; ocean circulations; air-sea interaction; interannual variability, including the Southern Oscillation and its attending El Nino; intraseasonal variability, including the Madden-Julian oscillation; climate variability and changes; and climate modeling. There is less emphasis on synoptic meteorology in the present edition, as it was covered quite adequately in the first edition. The main topic that is lacking is numerical weather prediction (NWP). This topic was originally envisioned as chapter 11, but it was decided to forego it because NWP developments and improvements generally are not so specific to a geographical region. Because of the increased interest in the Southern Hemisphere that followed FGGE, the American Meteorological Society formed an ad hoc committee (1981) and later a formal committee (1984) on meteorology and oceanography of the Southern Hemisphere, one of the functions of which is to plan and conduct professional scientific meetings. As a result, five international conferences on the meteorology and oceanography of the Southern Hemisphere have been held: in Brazil (1983), New Zealand (1986), Argentina (1989), Australia (1993), and South Africa (1997). The exchange of ideas at these conferences has been an important factor in the initiation of many of the studies that are summarized in this monograph.

Kasture, S. V. and R. N. Keshavamurty (1987). "Some aspects of the 30-50-day oscillation." Proceedings of the Indian Academy of Sciences (Earth and Planetary Sciences), Banglaore 96(1): 49-58.

The structure and interannual variability of the 30-50-day oscillation over the Indian region were studied during the monsoon season. The power spectra of the zonal component of wind show large power in the 30-50-day time scale. The oscillation has a meridional wavelength of similar to 25 degrees lat. and a slow northward phase speed of similar to 0.7 degrees lat./day. The oscillation also has some interannual variability. The periods are somewhat longer during the drought years.

Kawamura, R., M. Sugi, et al. (1998). "Recent extraordinary cool and hot summers in East Asia simulated by an ensemble climate experiment." Journal of the Meteorological Society of Japan, Tokyo, Japan 76(4): 597-617.

An ensemble of three 40-year parallel simulations was performed using a T42 AGCM version of the Japan Meteorological Agency global model to answer the question why extraordinary cool and hot summers in East Asia, especially Japan and Korea, tend to occur very frequently in recent years from the late 1970s to the early 1990s. Three independent long-term integrations from January 1955 to December 1994 were forced by the same SST boundary condition observed on the global scale. Our AGCM simulations employing prescribed observed SSTs were successful in reproducing extratropical circulation anomalies that bring about the decadal-scale amplitude modulation of interannual variations of summer mean temperatures in the vicinity of Japan. During the period from the beginning of 1980s to the early 1990s, the interannual variability of the east-west gradient of summertime SST anomalies between the South China Sea and the tropical western Pacific east of the Philippines became appreciably large, was accompanied by anomalous cumulus convection around the Philippines, and its phases coincided quite well with those of model-simulated lower-tropospheric geopotential height variations near Japan. The anomalous convective heating substantially affected summertime lower tropospheric circulation anomalies in East Asia through the dynamic process of the excitation of PJ teleconnection pattern (Nitta, 1987). The anomalous SST forcing from the tropics is crucially responsible for the frequent occurrence of extreme cool and hot summers in Japan and Korea from the late 1970s to the early 1990s. The presence of strong east-west gradient of SST anomalies across the Philippines is primarily attributed to the significant coupling of weak (strong) South Asian summer monsoon and the warm (cold) episode of ENSO. The warm episodes that occurred during the period from the late 1970s to the early 1990s are appreciably different from a typical model of El Nino event exemplified by Rasmusson and Carpenter (1982) in terms of seasonal evolution. It is anticipated that both unusually persistent ENSO signals from the preceding winter until summer and the associated South Asian summer monsoon activity strongly regulate the formation of the east-west SST gradient near the Philippines in boreal summer.

Kelkar, R. R. and A. Rao (1990). "Interannual variability of monsoon rainfall as estimated from INSAT-1B data." Mausam, New Delhi, India 41(2): 183-188.

Satellite estimated rainfall using INSAT-1B data is utilised to study the annual variations of monsoon rainfall during the years 1986, 1987 and 1988. Patterns of mean monthly rainfall for the monsoon months and the deviations from the mean of rainfall for each monsoon month are presented.

Khole, M. (1999). "SST over Indian Ocean during 1997 El-Nino event." Scientific correspondence Current Science, Bangalore, India 77(10): 1241-1245.

Several studies on possible correlation of Sea Surface Temperature (SST) over equatorial eastern Pacific and All-India Summer Monsoon Rainfall (AISMR) have been carried out recently super(1) super(-) super(5) . In general, warming over tropical eastern Pacific is associated with reduced AISMR activity, though there is no one-to-one correspondence between the two. Mooley super(6) has observed that the mean AISMR for El-Nino years during 1875-1996 is 8% below normal. The year 1997 witnessed one of the most severe El-Nino events of the present century. AISMR during 1997 was however, 102% of the Long Period Average (LPA). Besides the Pacific, the Indian Ocean (IO) which is geographically located very close to the Indian region, forms one of the three major ocean basins of the globe. Thus, it would be appropriate to examine the variation of SST over IO during the 1997 El-Nino event over the Pacific. This issue has been addressed in the study. Figure 1 shows Indian monthly rainfall, Southern Oscillation Index (SOI) and SST anomalies over NINO-3 region (5 degrees N-5 degrees S/150 degrees W-90 degrees W) starting from January 1996 to December 1998. Recently, Tourre and White super(7) super(,) super(8) by examining the interannual variability of SST, found the ENSO signal to be dominant in IO.

Kim, K. M. and K. M. Lau (2001). "Dynamics of monsoon-induced biennial variability in ENSO." Geophysical Research Letters, Washington, DC 28(2): 315-318.

Kim, S.-W. and Y. Isoda (1998). "Interannual variations of the surface mixed layer in the Tsushima Current region." Umi to Sora [Sea and Sky.], Kobe, Japan 74(1): 11-22.

At first, seasonal variations of the surface mixed layer depth (MLD) were examined by using the World Ocean Atlas data. It is found that the maximum MLD in the Tsushima Current region develops in February, and this MLD along the polar front is shallower than in its south and north sea areas. To investigate the interannual variations of MLD, therefore, we selected the temperature data in February over the PM-line, which is located in the central part of the Tsushima Current region during 25 years (1972-1996). The interannual variations of sea surface cooling, indicated by Monsoon Index (MOI) can not explain those of MLD and also the relationship between the MLD and the mixed layer temperature is a very poor. The MLD in this region is well correlated with the subsurface water temperatures deeper than 100m depth. The regression equation between water temperature at 200m depth and MLD is as the follows; MLD(m) = 12.5 x T sub(2) sub(0) sub(0) ( degrees C) + 66. It is suggested that the variations of MLD may be largely influenced by the interannual extension of warm waters of the Tsushima Current or the disposition of the local warm eddies. To quantitatively clarify the vertical structure of such warm eddy will be a very important subject in the heat balance of the Tsushima Current region to be investigated in the future.

Kitoh, A. (1992). "Simulated interannual variations of the Indo-Australian monsoons." Journal of the Meteorological Society of Japan, Tokyo, Japan 70(1B): 563-583.

Interannual variations of the South Asian and the Australian summer monsoons in a 20-year simulation by an atmospheric general circulation model (GCM) with the observed sea surface temperature (SST) for the period 1970-1989 are investigated. Emphasis is laid on moisture flux variations, as the moisture flux convergence plays a more dominant role in the rainfall variations than the local evaporation, although their relative roles are comparable for the 20-year mean moisture budget. The anomalous precipitation in the Bay of Bengal in boreal summer is significantly correlated with the SST anomalies in the western Pacific, but not with the in situ SST anomalies. The positive SST anomalies in the western Pacific are favorable to the intensified South Asian summer monsoon circulation with strong surface westerlies over the north Indian Ocean. A contrast in anomalous precipitation in the model between the South Arabian Sea and the India subcontinent is also discussed. The anomalous precipitation over the oceans north of Australia in austral summer is explained mainly by the anomalous moisture flux converging into this region from the west. This is accompanied by an intensified cyclonic circulation northwest of Australia, but cross-equatorial moisture flux from the winter hemisphere is found to be important. Some comparisons with observations are also made and discrepancies between the model and these observations are discussed.

Kondragunta, C. R. (1990). "On the intraseasonal variations of the Asiatic summer monsoon." Mausam, New Delhi, India 41(1): 11-20.

Intraseasonal fluctuations of the Asiatic summer monsoon are investigated using Outgoing Longwave Radiation (OLR) covering eight northern hemisphere summers (1 May to 30 September 1975-1983, except 1978). The intraseasonal variance is large in the equatorial Indian Ocean and the northwest Pacific. OLR fluctuations in the equatorial Indian Ocean, over India and the northwest Pacific show spectral peaks on time scales 30-60 days, 10-20 days and less than 10 days. This study also reveals intraseasonal variation associated with the interannual variation. Over India below normal summer rainfall years are associated with 30-60 oscillation, near normal summer rainfall years are associated with 30-60 day and 10-20 day oscillations and above normal rainfall years are associated with oscillations less than 10 days. Empirical Orthogonal Function (EOF) analysis has been carried out for the whole Asiatic summer monsoon domain. The first four EOF coefficients explain 15% of the total variance. EOF analysis confirms existence of oscillations at least on three time scales, viz., 30-60 days, 10-20 days and less than 10 days over the Asian summer monsoon region.

Kondragunta, C. R. (2001). "on the intraseasonal variations of the asiatic summer monsoon." Mausam [Mausam] 1: 217-226.

Intraseasonal flucturations of the Asiatic summer monsoon are investigated using Outgoing Longwave Radiation (OLR) covering eight northern hemisphere summers (1 May to 30 September 1975-83, except 1978). The intraseasonal variance is large in the equatorial Indian Ocean and the northwest Pacific. OLR fluctuations in the equatorial Indian Ocean, over India and the northwest Pacific show spectral peaks on time scales 30-60 day, 10-20 day and less than 10 days. This study also reveals intraseasonal variation associated with the interannual variation. Over India below normal summer rainfall years are associated with 30-60 oscillation, near normal summer rainfall years are associated with 30-60 day and 10-20 day oscillations and above normal rainfall years are associated with oscillations less than 10 days. Empirical Orthogonal Function (EOF) analysis has been carried out for the whole Asiatic summer monsoon domain. The first four EOF coefficients explain 15% of the total variance. EOF analysis confirms existence of oscillations at least on three time scales, viz., 30-60 day, 10-20 day and less than 10 days over the Asian summer monsoon region.

Kripalani, R. H., S. Inamdar, et al. (1996). "Rainfall variability over Bangladesh and Nepal: comparison and connections with features over India." International Journal of Climatology, Chichester, UK 16(6): 689-703.

In this study monthly rainfall data for 14 stations over Bangladesh for the period 1901-1977 are used to investigate and understand the interannual variability of the summer monsoon rainfall. Monthly, seasonal, and annual spatial rainfall patterns, and the spatial patterns of variability, are presented. Dominant structures of seasonal rainfall are determined through the empirical orthogonal functions. A homogeneous series for All Bangladesh Monsoon Rainfall is prepared and its temporal characteristics are studied. It is observed that the standardized rainfall for this series shows random fluctuations up to 1963, thereafter the standardized values are much above the normal values. Further the rainfall variations over Bangladesh are not related to large-scale variables such as the Northern Hemisphere surface temperature, Darwin pressure tendency, and the subtropical ridge over the Indian region. However, the rainfall variations over Bangladesh are related well with rainfall variations over northeast India. Similar analysis is done for the Nepal region by examining the monthly rainfall data over Kathmandu for a 105 year period (1851-1900, 1921-1975). Results reveal that Nepal rainfall is well related with rainfall variations over northern and central parts of India.

Kripalani, R. H., S. V. Singh, et al. (1995). "Variability of the summer monsoon rainfall over Thailand: comparison with features over India." International Journal of Climatology, Chichester, UK 15(6): 657-672.

In this study, 20 years (1961-1980) of rainfall data for 34 stations over Thailand are used to investigate and understand the intraseasonal and interannual variability of the summer monsoon. Dominant structures of 5-day and seasonal rainfall are determined through empirical orthogonal functions (EOFs). Monthly and seasonal spatial patterns and a map showing the coefficient of variation are also presented. On an intraseasonal time-scale regions with high 30-60-day variances (Madden Julian oscillations--MJOs) and 10-20-day variances (Quasi-biweekly oscillations--QBWOs) are identified using a band-pass Butterworth filter for 5-day rainfall. It is seen that the MJOs are dominant over the Indian region and the QBWOs are dominant over the Thailand region. Extended EOFs (EEOFs) have shown that the most important evolutionary feature over India is the northward propagation associated with the MJOs, whereas over the Thailand region it is westward, associated with the QBWOs. Northward propagation of rainfall anomalies is not observed over the Thailand region. On the interannual scale the area over northwest Thailand is related well with rainfall variation over west-central India. The Darwin pressure tendency (DPT) and the subtropical ridge over India shows significant relation with rainfall over northwest Thailand. However, the Northern Hemisphere surface temperature (NHST), Quasi-biennial Oscillation (QBO), and the West Pacific ridge (WPR) show no significant relation.

Krishna Kumar, K., K. Rupa Kumar, et al. (1987). "Comparison of Penman and Thornthwaite methods of estimating potential evapotranspiration for Indian conditions." Theoretical and Applied Climatology, Vienna 38(3): 140-146.

Thornthwaite's (1948) empirical method of estimating potential evapotranspiration (PE) has been preferred by several scientists in India to Penman's (1948) theoretical combination approach, because of the former's simplicity. However, in view of the doubts expressed in various quarters regarding the applicability of Thornthwaite's method for monsoon climates, a comparison is made of the performance of these two methods over different parts of India, by using similar to 26 yr of data at 15 stations spread over the country. Various aspects of the manifestations and their differences are presented. It is found that Thornthwaite's method gives higher estimates of PE and shows lower interannual variability than Penman's method during the southwest monsoon season. A systematic annual variation of the difference between the two methods is also noticed, which is found to be due mainly to the actual vapor pressure and sunshine duration included in Penman's method.

Krishnamurthy, V. and B. N. Goswami (2000). "Indian monsoon-ENSO relationship on interdecadal timescale." Journal of Climate, Boston, MA 13(3): 579-595.

Empirical evidence is presented to support a hypothesis that the interdecadal variation of the Indian summer monsoon and that of the tropical SST are parts of a tropical coupled ocean-atmosphere mode. The interdecadal variation of the Indian monsoon rainfall (IMR) is strongly correlated with the interdecadal variations of various indices of El Nino-Southern Oscillation (ENSO). It is also shown that the interannual variances of both IMR and ENSO indices vary in phase and follow a common interdecadal variation. However, the correlation between IMR and eastern Pacific SST or between IMR and Southern Oscillation index (SOI) on the interannual timescale does not follow the interdecadal oscillation. The spatial patterns of SST and sea level pressure (SLP) associated with the interdecadal variation of IMR are nearly identical to those associated with the interdecadal variations of ENSO indices. As has been shown earlier in the case of ENSO, the global patterns associated with the interdecadal and interannual variability of the Indian monsoon are quite similar. The physical link through which ENSO is related to decreased monsoon rainfall on both interannual and interdecadal timescales has been investigated using National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis products. The decrease in the Indian monsoon rainfall associated with the warm phases of ENSO is due to an anomalous regional Hadley circulation with descending motion over the Indian continent and ascending motion near the equator sustained by the ascending phase of the anomalous Walker circulation in the equatorial Indian Ocean. It is shown that, to a large extent, both the regional Hadley circulation anomalies and Walker circulation anomalies over the monsoon region associated with the strong (weak) phases of the interdecadal oscillation are similar to those associated with the strong (weak) phases of the interannual variability. However, within a particular phase of the interdecadal oscillation, there are several strong and weak phases of the interannual variation. During a warm eastern Pacific phase of the interdecadal variation, the regional Hadley circulation associated with El Nino reinforces the prevailing anomalous interdecadal Hadley circulation while that associated with La Nina opposes the prevailing interdecadal Hadley circulation. During the warm phase of the interdecadal oscillation, El Nino events are expected to be strongly related to monsoon droughts while La Nina events may not have significant relation. On the other hand, during the cold eastern Pacific phase of the interdecadal SST oscillation, La Nina events are more likely to be strongly related to monsoon floods while El Nino events are unlikely to have a significant relation with the Indian monsoon. This picture explains the observation that the correlations between IMR and ENSO indices on the interannual timescale do not follow the interdecadal oscillation as neither phase of the interdecadal oscillation favors a stronger (or weaker) correlation between monsoon and ENSO indices.

Krishnamurthy, V. and J. Shukla (2000). "Intraseasonal and interannual variability of rainfall over India." Journal of Climate, Boston, MA 13(24): 4366-4377.

A gridded daily rainfall dataset prepared from observations at 3700 stations is used to analyze the intraseasonal and interannual variability of the summer monsoon rainfall over India. It is found that the major drought years are characterized by large-scale negative rainfall anomalies covering nearly all of India and persisting for the entire monsoon season. The intraseasonal variability of rainfall during a monsoon season is characterized by the occurrence of active and break phases. During the active phase, the rainfall is above normal over central India and below normal over northern India (foothills of the Himalaya) and southern India. This pattern is reversed during the break phase. It is found that the nature of the intraseasonal variability is not different during the years of major droughts or major floods. This suggests that a simple conceptual model to explain the interannual variability of the Indian monsoon rainfall should consist of a linear combination of a large-scale persistent seasonal mean component and a statistical average of intraseasonal variations. The large-scale persistent component can be part of low-frequency components of the coupled ocean-land-atmosphere system including influences of sea surface temperature, snow, etc. The mechanisms responsible for the intraseasonal variations are not well understood. This simple conceptual framework suggests that the ability to predict the seasonal mean rainfall over India will depend on the relative contributions of the externally forced component and the intraseasonal component. To the extent that the intraseasonal component is intrinsically unpredictable, success in long-range forecasting will largely depend on accurate quantitative estimates of the externally forced component.

Krishnamurthy, V. and J. Shukla (2001). "Observed and model simulated interannual variability of the Indian monsoon." Mausam 52(1): 133-150.

The Center for Ocean-Land-Atmosphere (COLA) general circulation model has been integrated seven times with observed global sea surface temperature (SST) for the years 1979-98. The model-simulated annual cycle, the seasonal mean and the interannual variability of the summer monsoon rainfall and circulation over the Indian region are compared with the corresponding observations. It is found that, although this model has shown remarkable success in simulating the local and global response of tropical SST anomalies, the model shows poor skill in simulating the interannual variability of monsoon rainfall over India. While it is true that the correlation between the observed tropical Pacific SST and the Indian summer monsoon rainfall for the most recent 20 years itself is considerably lower than that for other 20-year periods in the past, it is likely that the model's inability to simulate rainfall variability over India is largely related to the systematic errors of the model in simulating the climatological mean monsoon circulation and rainfall, especially over the oceanic regions.

Krishnamurti, T. N., N. Surgi, et al. (1985). "Annual cycle of the monsoon over the global Tropics." World Meteorological Organization, Geneva, WCRP Publications Series No(65).

The authors examine the summer and winter patterns of the divergent circulations during 1978-1978, represented by the Indian summer monsoon, the African monsoon, and the divergent motion in the eastern Pacific Ocean immediately adjacent to Central America, which is a highly convective region during the northern summer. A longer term variability of the rotational and divergent motions at 200 mb is also investigated. The aforementioned divergent circulations are discussed: a three-dimensional view of the divergent circulations; the scales of E-W circulations; periods of explosive growth of kinetic energy during FGGE; and interannual variability in the mean monthly and annual motion field. Most of the variance of divergent circulation on a horizontal was noted during both periods. The winter situation exhibited a readjustment of the Hadley cell with a response of the zonal flows, whereas the summer increase of kinetic energy (during the onset of monsoons) is largely attributed to the interactions among the divergent and rotational components. On interannual time scales, tropical, divergent, and nondivergent circulations exhibited interesting contrasts during El Nino and non-El Nino years. The nondivergent flow anomalies show the evolution of a long-lasting western wind anomaly and an associated low pressure to its north over the monsoon region in the upper troposphere. The size and intensity of this pressure anomaly exceed the pressure anomalies associated with the Pacific North American patterns. Another aspect of the anomaly patterns is a major shift to the southeast of the divergent circulations.

Krishnan, R. and S. V. Kasture (1996). "Modulation of low frequency intraseasonal oscillations of northern summer monsoon by El Nino and Southern Oscillation (ENSO)." Meteorology and Atmospheric Physics, Vienna, Austria 60(4): 237-257.

In order to improve our understanding of the interannual variability of the 30-50 day oscillations of the northern summer monsoon, we have performed numerical experiments using a 5-level global spectral model (GSM). By intercomparing the GSM simulations of a control summer experiment (E1) and a warm ENSO experiment (E2) we have examined the sensitivity of the low frequency intraseasonal monsoonal modes to changes in the planetary scale component of the monsoon induced by anomalous heating in the equatorial eastern Pacific during a warm ENSO phase. It is found that the anomalous heating in the equatorial eastern Pacific induces circulation changes which correspond to weakening of the time-mean divergent planetary scale circulation in the equatorial western Pacific, weakening of the east-west Walker cell over the western Pacific ocean, weakening of the time-mean Reverse Hadley circulation (RHC) over the summer monsoon region and strengthening of the time-mean divergent circulation and the subtropical jet stream over the eastern Pacific and Atlantic oceans. These changes in the large scale basic flow induced by the anomalous heat source are found to significantly affect the propagation characteristics of the 30-50 day oscillations. It is noticed that the reduction (increase) in the intensity of the time-mean divergent circulation in the equatorial western (eastern) Pacific sectors produces weaker (stronger) low-level convergence as a result of which the amplitude of the eastward propagating 30-50 day divergent wave decreases (increases) in the western (eastern) Pacific sectors in E2. One of the striking aspects is that the eastward propagating equatorial wave arrives over the Indian longitudes more regularly in the warm ENSO experiment (E2). The GSM simulations reveal several small scale east-west cells in the longitudinal belt between 0-130 degrees E in the E1 experiment. On the other hand the intraseasonal oscillations in E2 show fewer east-west cells having longer zonal scales. The stronger suppression of small scale east-west cells in E2 probably accounts for the greater regularity of the 30-50 day oscillations over the Indian longitudes in this case. The interaction between the monsoon RHC and the equatorial 30-50 day waves leads to excitation of northward propagating modes over the Indian subcontinent in both cases. It is found that the zonal wind perturbations migrate northward at a rate of about 0.8 degrees latitude per day in E1 while they have a slightly faster propagation speed of about 1 degrees latitude per day in E2. The low frequency monsoonal modes have smaller amplitude but possess greater regularity in E2 relative to E1. As the wavelet trains of low latitude anomalies progress northward it is found that the giant meridional monsoonal circulation (RHC) undergoes well-defined intraseasonal oscillations. The amplitude of the monsoon RHC oscillations are significantly weaker in E2 as compared to E1. But what is more important is that the RHC is found to oscillate rapidly with a period of 40 days in E1 while it executes slower oscillations of 55 days period in E2. These results support the observational findings of Yasunari (1980) who showed that the cloudiness fluctuations on the 30-60 day time scale over the Indian summer monsoon region are associated with longer periods during El Nino years. The oscillations of the monsoon RHC show an enhancement of the larger scale meridional cells and also a stronger suppression of the smaller scale cells in E2 relative to E1 which seems to account for the slower fluctuations of the monsoon RHC in the warm ENSO experiment. It is also proposed that the periodic arrival of the eastward propagating equatorial wave over the Indian longitudes followed by a stronger inhibition of the smaller meridional scales happen to be the two primary mechanisms that favour steady and regular northward propagation of intraseasonal transients over the Indian subcontinent in the warm ENSO experim

Kulkarni, J. R. and R. K. Verma (1993). "On the spatio-temporal variations of the tropopause height over India and Indian Summer Monsoon Activity." Advances in Atmospheric Sciences, Beijing, China 10(4): 481-488.

The spatio-temporal variation of the tropopause height (TH) over the Indian region (5 degrees N-35 degrees N, 70 degrees E-95 degrees E) has been studied using monthly mean TH data, for a 22-year period, 1965 to 1986. The study revealed that the stations south of 20 degrees N showed maximum TH in April/May and minimum in September. This variation in TH has been attributed to the corresponding variation of average surface temperature (SST) over plus or minus 20 degrees latitudinal belt over Indian Ocean, Arabian Sea and Bay of Bengal. Further the stations north of 20 degrees N showed maximum in June and minimum in October/November. This maximum in TH has primarily been attributed to the increased insolation and convection. Furthermore it is noticed that the anomaly of TH moved northwards during the period April to July. The interannual variability of the Indian Summer Monsoon Activity (ISMA) has been studied in relation to all India mean TH (at 12 GMT) for six months April through September. The composites of mean TH for good and bad monsoon year showed that all India mean TH is statistically higher in good monsoon years than in bad monsoon years. The relationship between IMSA and all India mean May TH has been studied using the contingency table. The study suggested that the forecast of ISMA could be prepared using mean May TH.

Kumar, J. R. and D. S. Desai (1999). "Monsoon variability in recent years from synoptic scale disturbances and semi-permanent systems." Mausam 50(2): 135-144.

In the recent decade from 1987 to 1996, the Indian summer monsoon rainfall has shown less interannual variability in comparison with its earlier decade. Except 1987 and 1988, the area weighted average monsoon rainfall of all other years are within plus or minus 10% (normal) of its long period average value over India. The paper discusses monsoon rainfall and several other associated circulations features with their variability in interannual scale during 1987-96. The results show that though the variability of monsoon rainfall is less during the decade, there is a significant interannual variation in the number of synoptic systems, their days, intensities and number of days of presence of monsoon trough and Tibetan anticyclone. The years with positive side (negative side) of normal seasonal rainfall are characterised by more (less) number of days of synoptic disturbances and more (less) number of days of presence of monsoon trough and Tibetan anticyclone in their favourable positions. However, overall activity of heat low, tropical easterly jet and sub-tropical westerly jet in the season have no direct relation with seasonal monsoon rainfall. In addition, the dates of onset and withdrawal of monsoon over India and the number of days monsoon took to over all India also have no relation with the monsoon rainfall.

Kumar, K., M. K. Soman, et al. (1995). "Seasonal forecasting of Indian summer monsoon rainfall: a review." Weather, Bracknell, England 50(12): 449-466.

The long-range forecasting of Indian monsoon rainfall is at present almost solely based on statistical formulations; the utility of numerical weather prediction for this purpose is still to be established. Although the atmospheric GCMs can reproduce the interannual variations of monsoon circulation in response to tropical SST anomalies, the simulations of interannual monsoon rainfall fluctuations are very poor. As the Indian monsoon rainfall simulation is found to be extremely sensitive to initial conditions, some suitable integration procedures have to be devised for seasonalforecasting. While the issues of deterministic predictability of the monsoon rainfall on a seasonal scale are yet to be resolved, optimizing the accuracy of the forecast through the use of empirical models and a proper selection of predictands, predictors and methodology has immediate practical applications. Techniques other than multiple regression need to be explored for better predictive potential. Any further improvement of predictive skill depends upon the identification of non-ENSO forcing on the monsoon, which so far has remained elusive.

Kumar, M. and T. G. Prasad (1997). "Annual and interannual variation of precipitation over the tropical Indian Ocean." Journal of Geophysical Research, Washington, DC 102(C8): 18519-18527.

The annual and interannual variability of precipitation over the tropical Indian Ocean is studied for the period June 1986 to December 1990 using the data retrieved from the Indian National Satellite (INSAT). The seasonal and annual rainfall over the Bay of Bengal was found to be about 2-3 times the Arabian Sea values. Harmonic analysis of the monthly mean rainfall showed that the annual wave has its largest amplitude in the northern Bay of Bengal, where the amplitude exceeds 250 mm/month, and the lowest amplitudes are found in the western Indian Ocean, especially off the Arabian and east African coasts. The INSAT and GOES Precipitation Index (GPI) rainfall estimates correlated reasonably well with the island rainfall data, with correlation coefficients of 0.83 and 0.78, respectively, whereas the special sensor microwave imager (SSMI) rainfall estimates had the lowest correlation (r=0.64) with the island rainfall data. A comparison of the mean annual estimates by the three methods showed that the GPI rainfall estimates were higher than the INSAT and SSMI estimates by 16% and 41%, respectively, for the Indian Ocean area. The INSAT, GPI and SSMI rainfall estimates document significant variations (both annual and seasonal) for all the study areas, with the Indian Ocean area exhibiting maximum variability during the summer monsoon (June, July, and August) season.

Lal, M., L. Bengtsson, et al. (1995). "Synoptic scale disturbances of the Indian summer monsoon as simulated in a high resolution climate model." Climate Research, Oldendorf, Luhe, Germany 5(3): 243-258.

The Hamburg atmospheric general circulation model ECHAM3 at T106 resolution (1.125 degrees lat./lon.) has considerable skill in reproducing the observed seasonal reversal of mean sea level pressure, the location of the summer heat low as well as the position of the monsoon trough over the Indian subcontinent. The present-day climate and its seasonal cycle are realistically simulated by the model over this region. The model simulates the structure, intensity, frequency, movement and lifetime of monsoon depressions remarkably well. The number of monsoon depressions /storms simulated by the model in a year ranged from 5 to 12 with an average frequency of 8.4 yr super(-) super(1) , not significantly different from the observed climatology. The model also simulates the interannual variability in the formation of depressions over the north Bay of Bengal during the summer monsoon season. In the warmer atmosphere under doubled CO sub(2) conditions, the number of monsoon depressions/cyclonic storms forming in Indian seas in a year ranged from 5 to 11 with an average frequency of 7.6 yr super(-) super(1) , not significantly different from those inferred in the control run of the model. However, under doubled CO sub(2) conditions, fewer depressions formed in the month of June. Neither the lowest central pressure nor the maximum wind speed changes appreciably in monsoon depressions identified under simulated enhanced greenhouse conditions. The analysis suggests there will be no significant changes in the number and intensity of monsoon depressions in a warmer atmosphere.

Lal, M., T. Nozawa, et al. (2001). "Future climate change: Implications for Indian summer monsoon and its variability." Current Science 81(9): 1196-1207.

The broad climatological features associated with the Asian monsoon circulation, including its mean state and intraseasonal and interannual variability over the Indian subcontinent, as simulated in the CCSR/NIES coupled A-O GCM in its control experiment are presented in this paper. The model reproduces the seasonal cycle as well as basic observed patterns of key climatic parameters, in spite of some limitations in simulation of the monsoon rainfall. While the seasonality in rainfall over the region is well simulated and the simulated area-averaged monsoon rainfall is only marginally higher than the observed rainfall, the peak rainfall is simulated to be about two-thirds of the observed precipitation intensity over central India. The transient experiments performed with the model following the four SRES 'Marker' emission scenarios, which include revised trends for all the principal anthropogenic forcing agents for the future, suggest an annual mean area-averaged surface warming over the Indian subcontinent to range between 3.5 and 5.5 degree C over the region during 2080s. During winter, India may experience between 5 and 25% decline in rainfall. The decline in wintertime-rainfall over India is likely to be significant and may lead to droughts during the dry summer months. Only a 10 to 15% increase is projected in area-averaged summer monsoon rainfall over the Indian subcontinent. The date of onset of summer monsoon over India could become more variable in future.

Lal, M., K. K. Singh, et al. (1999). "Growth and yield responses of soybean in Madhya Pradesh, India to climate variability and change." Agricultural and Forest Meteorology, Amsterdam, The Netherlands 93(1): 53-70.

This study is aimed at assessing the impact of thermal and moisture stresses associated with observed intraseasonal and interannual variability in key climatic elements on the nature and extent of losses in growth and yield of soybean crop in central India through the use of CROPGRO model. The crops are found to be more sensitive to higher cumulative heat units during cropping season. The yields respond substantially to temporal variations in rainfall (associated with observed swings in the continuity of monsoon). Prolonged dry spells at critical life stages of the soybean crop are found to adversely affect crop development and growth and hence the yields at selected sites. We have also examined the plausible effects of future climate change on soybean yields in the selected region based on simulations carried out for doubled atmospheric CO sub(2) level and with modified weather variables using the available seasonal projections for the future. Our findings on the response of elevated CO sub(2) concentrations in the atmosphere suggest higher yields (50% increase) for soybean crop for a doubling of CO sub(2) . However, a 3 degrees C rise in surface air temperature almost cancels out the positive effects of elevated CO sub(2) on the yield. Soybean crops at selected site are more vulnerable to increases in maximum temperature than in minimum temperature. The combined effect of doubled CO sub(2) and anticipated thermal stress (likely by middle of the next century) on soybean crop is about 36% increase in yield at the selected sites. A decline in daily rainfall amount by 10% restricts this yield gain to about 32%. Deficient rainfall with uneven distribution during the monsoon season could be a critical factor for the soybean productivity even under the positive effects of elevated CO sub(2) in the future.

Lang, T. J. and A. P. Barros (2002). "An Investigation of the Onsets of the 1999 and 2000 Monsoons in Central Nepal." Monthly Weather Review 130(5): 1299-1316.

The Marsyandi River basin in the central Nepalese Himalayas is a topographically complex region, with strong spatial gradients of precipitation over various timescales. A meteorological network consisting of 20 stations was installed at a variety of elevations (528-4435 m) in this region, and measurements of rainfall were made during the 1999 and 2000 summer monsoons. The onsets of the 1999 and 2000 monsoons in central Nepal were examined at different spatial scales by using a combination of rain gauge, Meteosat-5, Tropical Rainfall Measuring Mission (TRMM), ECMWF analysis, and Indian radiosonde data. At the network, the onsets manifested themselves as multiday rain events, which included a mixture of stratiform and convective precipitation. Moist and unstable upslope flow was associated with the occurrence of heavy rainfall. During each onset, 2-day rainfall reached as high as 462 mm, corresponding to 10%-20% of the monsoon rainfall. Differences among rain gauges were up to a factor of 8, reflecting the role of small-scale terrain features in modulating rainfall amounts. At the larger scale, the onsets were associated with monsoon depressions from the Bay of Bengal that moved close enough to the Himalayas to cause the observed upslope flow from the winds on their eastern flank. During the 1999 onset, convection in this eastern flank collided with the mountains in the vicinity of the network. In 2000 no major collision occurred, and 33%-50% less rain than 1999 fell. Analysis of observations for a 5-yr period (1997-2001) suggests that the interannual variability of the monsoon onset along the Himalayan range is linked to the trajectories and strength of these depressions.

Lanzante, J. R. (1985). "Further studies of singularities associated with the semiannual cycle of 700-mb heights." Monthly Weather Review, Boston 113(8): 1372-1378.

An investigation of singularities associated with the semiannual cycle of Northern Hemisphere (25-90 degrees N) 700-mb heights was conducted by using 33 yr of data. Extension of the harmonic analyses of Lanzante (1983) to a larger domain revealed the importance of the semiannual cycle to the seasonal progression of heights over subtropical Asia; this is undoubtedly a reflection of the Asiatic monsoon. From a global perspective, the semiannual cycle varies in such a way that this Asiatic region is out of phase with a region stretching from northeastern Siberia to the Gulf of Alaska, as well as the subtropical Atlantic and eastern Pacific. Furthermore, it is suggested that the semiannual cycle is reflected regionally in the persistence of height anomalies as reported by van den Dool and Livezey (1984). Indices for nine regions of a relatively large, explained variance and a uniform phase angle of the second harmonic of heights were derived in order to quantify interannual variations in the semiannual cycle. Frequency distributions of parameters, based upon 25-day and seasonal aggregates of the daily indices were largely Gaussian. It is concluded that (for the time averages considered) there is no indication that the indices come from two populations representing either the occurrence or nonoccurrence of an amplified semiannual cycle. Finally, interannual relationships among the nine indices were investigated through auto- and cross-correlation analyses; the results were largely negative.

Latif, M., K. Sperber, et al. (2001). "ENSIP: the El Nino simulation intercomparison project." Climate Dynamics 18(3/4): 255-276.

An ensemble of twenty four coupled ocean-atmosphere models has been compared with respect to their performance in the tropical Pacific. The coupled models span a large portion of the parameter space and differ in many respects. The intercomparison includes TOGA (Tropical Ocean Global Atmosphere)-type models consisting of high-resolution tropical ocean models and coarse-resolution global atmosphere models, coarse-resolution global coupled models, and a few global coupled models with high resolution in the equatorial region in their ocean components. The performance of the annual mean state, the seasonal cycle and the interannual variability are investigated. The primary quantity analysed is sea surface temperature (SST). Additionally, the evolution of interannual heat content variations in the tropical Pacific and the relationship between the interannual SST variations in the equatorial Pacific to fluctuations in the strength of the Indian summer monsoon are investigated. The results can be summarised as follows: almost all models (even those employing flux corrections) still have problems in simulating the SST climatology, although some improvements are found relative to earlier intercomparison studies. Only a few of the coupled models simulate the El Nino/Southern Oscillation (ENSO) in terms of gross equatorial SST anomalies realistically. In particular, many models overestimate the variability in the western equatorial Pacific and underestimate the SST variability in the east. The evolution of interannual heat content variations is similar to that observed in almost all models. Finally, the majority of the models show a strong connection between ENSO and the strength of the Indian summer monsoon.

Latif, M., A. Sterl, et al. (1994). "Climate variability in a coupled GCM. Part II: The Indian Ocean and monsoon." Journal of Climate, Boston, MA 7(10): 1449-1462.

We have investigated the seasonal cycle and the interannual variability of the tropical Indian Ocean circulation and the Indian summer monsoon simulated by a coupled ocean-atmosphere general circulation model in a 26-year integration. Although the model exhibits significant climate drift, overall, the coupled GCM simulates realistically the seasonal changes in the tropical Indian Ocean and the onset and evolution of the Indian summer monsoon. The amplitudes of the seasonal changes, however, are underestimated. The coupled GCM also simulates considerable interannual variability in the tropical Indian Ocean circulation, which is partly related to the El Nino/Southern Oscillation phenomenon and the associated changes in the Walker circulation. Changes in the surface wind stress appear to be crucial in forcing interannual variations in the Indian Ocean SST. As in the Pacific Ocean, the net surface heat flux acts as a negative feedback on the SST anomalies. The interannual variability in monsoon rainfall, simulated by the coupled GCM, is only about half as strong as observed. The reason for this is that the simulated interannual variability in the Indian monsoon appears to be related to internal processes within the atmosphere only. In contrast, an investigation based on observations shows a clear lead-lag relationship between interannual variations in the monsoon rainfall and tropical Pacific SST anomalies. Furthermore, the atmospheric GCM also fails to reproduce this lead-lag relationship between monsoon rainfall and tropical Pacific SST when run in a stand-alone integration with observed SSTs prescribed during the period 1979-1988. These results indicate physical processes relating tropical Pacific SST to Indian monsoon rainfall are not adequately modeled in our atmospheric GCM. Monsoon rainfall predictions appear therefore premature.

Lau, K. M. (1992). "East Asian summer monsoon rainfall variability and climate teleconnection." Journal of the Meteorological Society of Japan, Tokyo, Japan 70(1B): 211-242.

In this paper, recent progress in the study of the East Asian summer monsoon (EAM) and its impact on global climate fluctuations are reviewed. The review is focused on the climatology and variability of the EAM rainfall and its relationship with regional and global scale circulation systems. Climatologically, the EAM rainfall is dominated by convective activities associated with the northward advance of the Mei-yu trough from southern China during April-May to central China during mid-June. After staying in the same position for one to two weeks, the Mei-yu trough disappears abruptly and a new rainfall zone is developed over northern China. This is followed by a quasi-20 days oscillatory rainfall regime which develops over central China. Subsequently, the maximum rainfall zone returns to the coastal region of south and southeast China. Regional features unique to the EAM include the extraordinary length of the extended monsoon season (April to late August), the extent of the northward penetration of the major precipitation, the multiple onset and interspersed propagation and stationary nature of the rainfall. Planetary scale features that directly influence the EAM include the western Pacific Subtropical High, the Tibetan High, the local Hadley and the equatorial Walker circulations. It is stressed that the EAM rainfall is only a small part of the global scale precipitation system which migrates northward from the equatorial Indian Ocean and the Western Pacific to the EAM region and Indian subcontinent during the boreal summer. The EAM possesses a wide range of spatial and temporal scales of variabilities including the seasonal cycle, intraseasonal oscillations, subseasonal scale inter-monsoon interactions, sub-synoptic scale variability and supercluster organization in the western Pacific. These variabilities are in turn linked to interannual variations associated with the biennial oscillation and the El Nino/Southern Oscillation. Also discussed is evidence showing the presence of an atmospheric teleconnection pattern connecting eastern Asia and North America (ANA) via the North Pacific. The ANA has profound impact on the climate of eastern Asia including Japan. Dynamically, it may be associated with a marginally unstable barotropic mode in the mean Northern Hemisphere summertime circulation. This mode is also related to latent heating in the western Pacific near the Philippines as well as the Indian Ocean region. While there are some successes in the general circulation model (GCM) simulation of the planetary scale features of the EAM, most GCMs still have problems obtaining realistic regional rainfall over East Asia and India. The intraseasonal and interannual variability of the EAM are generally not very well-simulated in GCMs. Much work is needed to improve modeling of the variability of the EAM.

Lau, K. M. and W. Bua (1998). "Mechanisms of monsoon-Southern Oscillation coupling: insights from GCM experiments." Climate Dynamics 14(11): 759-779.

The relative roles of internal atmospheric dynamics, land surface evaporation and sea surface temperature (SST) forcings on the coupling between the Asian monsoon (AM) and the Southern Oscillation (SO) are investigated in a series of GCM experiments. Results confirm previous studies indicating that the characteristic large-scale pattern of the SO is due primarily to SST anomaly (SSTA) forcing. The AM circulation anomalies are coupled to the SO via a characteristic upper level circulation couplet over the equatorial central Pacific. This couplet acts as a radiating node for teleconnection signals originating from the AM region to the extratropics. Generally, a weak AM is associated with warm SST over the eastern equatorial Pacific, concomitant with the negative phase of the SO, i.e., low (high) surface pressure over Tahiti (Darwin). The reverse holds for strong AM. Two wavetrains associated with the AM fluctuation have been identified: one arcing over northeastern Asia via the Aleutians to North American, and another emanating from northwestern Europe, via Siberia to northern India. Internal dynamics appear to underpin the origin of these wavetrains, which are strongly tempered by SSTA forcing and to a lesser degree by interactive land processes. Regionally, land-atmosphere interaction seems to have the strongest impact over East Asia/Indochina and the adjacent oceanic region of the South China Sea. Here, land-atmosphere interaction is responsible for the enhancement of a subseasonal scale see-saw oscillation in precipitation between land and the adjacent oceans. A local land-atmosphere feedback mechanism involving strong coupling between the hydrologic and energy cycles is identified. It is suggested that the interaction among precipitation, moisture convergence and land surface turbulent heat fluxes and radiation processes play key roles in determining the fast (subseasonal and shorter scales) response of the AM. On these time scales, the occurrences of cool/wet and hot/dry states associated with the precipitation seesaw appear to be chaotic. However, the preferred occurrence of a given state and the abrupt transition between states are dependent on the large-scale circulation and radiation forcings induced by the SO. One of the more provocative findings here is that effects of land-atmosphere interaction do not seem to alter the basic planetary scale features of the AM-SO system. As a result, the interannual variability of the coupled AM-SO is relatively small in the absence of anomalous SST forcing. Yet, the local effect of land-atmosphere interaction on AM is quite pronounced and dependent upon the large-scale forcings related to SO.

Lau, K. M. and W. Bua (1998). "Mechanisms of monsoon-Southern Oscillation coupling: insights from GCM experiments." Climate Dynamics, Berlin, Germany 14(11): 759-779.

The relative roles of internal atmospheric dynamics, land surface evaporation and sea surface temperature (SST) forcings on the coupling between the Asian monsoon (AM) and the Southern Oscillation (SO) are investigated in a series of GCM experiments. Results confirm previous studies indicating that the characteristic large-scale pattern of the SO is due primarily to SST anomaly (SSTA) forcing. The AM circulation anomalies are coupled to the SO via a characteristic upper level circulation couplet over the equatorial central Pacific. This couplet acts as a radiating node for teleconnection signals originating from the AM region to the extratropics. Generally, a weak AM is associated with warm SST over the eastern equatorial Pacific, concomitant with the negative phase of the SO, i.e., low (high) surface pressure over Tahiti (Darwin). The reverse holds for strong AM. Two wavetrains associated with the AM fluctuation have been identified: one arcing over northeastern Asia via the Aleutians to North America, and another emanating from northwestern Europe, via Siberia to northern India. Internal dynamics appear to underpin the origin of these wavetrains, which are strongly tempered by SSTA forcing and to a lesser degree by interactive land processes. Regionally, land-atmosphere interaction seems to have the strongest impact over East Asia/Indochina and the adjacent oceanic region of the South China Sea. Here, land-atmosphere interaction is responsible for the enhancement of a subseasonal scale see-saw oscillation in precipitation between land and the adjacent oceans. A local land-atmosphere feedback mechanism involving strong coupling between the hydrologic and energy cycles is identified. It is suggested that the interaction among precipitation, moisture convergence and land surface turbulent heat fluxes and radiation processes play key roles in determining the fast (subseasonal and shorter scales) response of the AM. On these time scales, the occurrences of cool/wet and hot/dry states associated with the precipitation seesaw appear to be chaotic. However, the preferred occurrence of a given state and the abrupt transition between states are dependent on the large-scale circulation and radiation forcings induced by the SO. One of the more provocative findings here is that effects of land-atmosphere interaction do not seem to alter the basic planetary scale features of the AM-SO system. As a result, the interannual variability of the coupled AM-SO is relatively small in the absence of anomalous SST forcing. Yet, the local effect of land-atmosphere interaction on AM is quite pronounced and dependent upon the large-scale forcings related to SO.

Lau, K. M. and C.-P. Chang (1987). "Planetary-scale aspects of the winter monsoon and atmospheric teleconnections." Chang, Chih Pei.

This paper documents the characteristics of the planetary-scale winter monsoon system mainly on the basis of results of several recent observational studies such as the First GARP (Global Atmospheric Research Program) Global Experiment/Monsoon Experiment (FGGE /MONEX). The following topics are discussed: 1) seasonal mean fields; 2) short-term fluctuations of the time scales of a few days, including cold surge genesis, regional energetics, midlatitude tropical interactions (active monsoon periods and winter MONEX), jet stream dynamics, and interhemispheric interactions; 3) intraseasonal variations, including tropical 40-50-day oscillations, atmospheric teleconnections (extratropical pattern, tropical-extratropical pattern), and 30-day oscillations; 4) interannual variability, including teleconnection in rainfall anomalies, winter monsoon during the 1982-1983 ENSO, cold surges and ENSO, and possible interpretation of the interannual variability of the winter monsoon in terms of a bimodal climatic state found over the Tropical Pacific ocean-atmosphere system.

Lau, K. M., C. P. Chang, et al. (1983). "Short-term planetary-scale interactions over the Tropics and midlatitudes, Pt. 2, Winter-MONEX period." Monthly Weather Review, Boston 111(7): 1372-1388.

Short-term teleconnections over the Pacific sector of the Tropics and the midlatitudes in relation to monsoonal surges during the winter of 1978-1979 are investigated by using 850- and 200-mb wind data from FGGE/Winter-MONEX. Results show that the intensification of the 200-mb jet streak over Japan is a precursor of cold surges and subsequent downstream development over the central Pacific. A large part of the transient variation of the jet at the entrance region near northeastern China is controlled by the upper level ageostrophic flow transverse to the jet, whereas elsewhere, the contribution by momentum flux convergence is more important. It is found that the interaction between cold surges and tropical convection over the maritime continent of Borneo and Indonesia basically agrees with the model of Chang and Lau (1980) and Part 1 of this paper, except that the intensity of the interaction was much weaker during Winter-MONEX. A new feature observed during the Winter-MONEX period is that the main convective heat source was found over the equatorial central Pacific and was enhanced 3-4 days after the surge onset. The enhancement coincided with the occurrence of a subtropical jet stream over Hawaii and a pronounced upper level trough-ridge system extending from the equatorial central Pacific to the west coast of North America. It is also hypothesized that the abnormally weak surges during Winter-MONEX may be a result of the reduced positive feedback between the tropical convection over the maritime continent and midlatitude disturbances near the east coast of China because of the remoteness of the primary tropical heat source from the surge area. The apparent downstream teleconnection observed during the postsurge periods suggests enhanced midlatitude-tropical coupling over the central Pacific which may have strong influence on synoptic developments over the west coast of the U.S. Notwithstanding possible uncertainties for the results in the Tropics, the study suggests that midlatitude systems are capable of forcing tropical convection which may give rise to midlatitude remote responses. Comparison of this study with Part 1 and other related work also reveals some interesting aspects of the interannual variability of short-term planetary-scale interactions.

Lau, K. M., K. M. Kim, et al. (2000). "Dynamical and boundary forcing characteristics of regional components of the Asian summer monsoon." Journal of Climate, Boston, MA 13(14): 2461-2482.

In this paper, the authors present a description of the internal dynamics and boundary forcing characteristics of two major subcomponents of the Asian summer monsoon (ASM), that is, the South Asian monsoon (SAM) and the East-Southeast Asian monsoon (EAM). The description is based on a new monsoon-climate paradigm in which the variability of ASM is considered as the outcome of the interplay of a ``fast'' and an ``intermediate'' monsoon subsystem, under the influence of ``slow'' external forcings. Two sets of regional monsoon indices derived from dynamically consistent rainfall and wind data are used in this study. Results show that the internal dynamics of SAM are representative of a ``classical'' monsoon system in which the anomalous circulation is governed by Rossby wave dynamics, where anomalous vorticity induced by an off-equatorial heat source is balanced by the advection of planetary vorticity. On the other hand, the internal dynamics of EAM are characterized by a ``hybrid'' monsoon system featuring multicellular meridional circulation over the East Asian sector, extending from the deep Tropics to the midlatitudes. These meridional cells link tropical heating to extratropical circulation systems via the East Asian jet stream and are responsible for the observed zonally oriented anomalous rainfall patterns over East and Southeast Asia and the subtropical western Pacific. In the extratropical regions, the major upper-level vorticity balance is between the advection and generation by anomalous divergent circulation and basic-state circulation. A consequence of the different dynamical underpinnings is that EAM is associated with stronger extratropical teleconnection patterns to regions outside ASM compared to SAM. The interannual variability of SAM is linked to basin-scale SST fluctuation with pronounced signals in the equatorial eastern Pacific. During the boreal spring, warming of the Arabian Sea and the subtropical western Pacific may lead to a strong SAM. For EAM, interannual variability is tied to SST anomalies over the East China Sea, the Sea of Japan (East Sea), and the South China Sea regions, while the linkage to equatorial basin-scale SST anomaly is weak at best. A strong EAM is foreshadowed by a large-scale SST anomaly dipole with warming (cooling) in the subtropical central (eastern) Pacific. Comparison with the P. J. Webster and S. Yang (WY) monsoon index shows that WY is not significantly correlated with either the SAM or EAM regional-scale rainfall separately. It is demonstrated that WY can be considered as a measure of the large-scale atmospheric circulation state over the Indian/Pacific Ocean basin, including the integrated heat source over the ASM region. As such, the regional monsoon indices developed in this paper and WY provide a complementary description of the broadscale and regional aspects of the ASM.

Lau, K. M. and H. T. Wu (2001). "Principal Modes of Rainfall-SST Variability of the Asian Summer Monsoon: A Reassessment of the Monsoon-ENSO Relationship." Journal of Climate 14(13): 2880-2895.

Using global rainfall and sea surface temperature (SST) data for the past two decades (1979-98), the covariability of the Asian summer monsoon (ASM) and El Nino-Southern Oscillation (ENSO) was investigated. The findings suggest three recurring rainfall-SST coupled modes. Characterized by a pronounced biennial variability, the first mode is associated with generally depressed rainfall over the western Pacific and the "Maritime Continent," stemming from the eastward shift of the Walker circulation during the growth phase of El Nino. The associated SST pattern consists of an east-west SST seesaw across the Pacific and another seesaw with opposite polarity over the Indian Ocean. The second mode is associated with a growing La Nina, comprising mixed, regional, and basin-scale rainfall and SST variability with abnormally warm water in the vicinity of the Maritime Continent and western Pacific. It possesses a pronounced low-level west Pacific anticyclone (WPA) near the Philippines and exhibits large subseasonal-scale variability. The third mode is associated with regional coupled ocean-atmosphere processes in the ASM region, having spatial and temporal variabilities that suggest extratropical linkages and interhemispheric interactions occurring on decadal timescales. Results indicate the importance of regional processes in affecting ASM rainfall variability. On the average, and over the ASM region as a whole, ENSO-related basin-scale SSTs can account for about 30% of the variability, and regional processes can account for an additional 20%. In individual years and over subregions, the percentages can be much higher or lower. In addition to the shift in the Walker circulation, it is found that the regional excitation of the WPA is important in determining the rainfall variability over south Asia and east Asia. Based on the results, a hypothesis is proposed that anomalous wind forcings derived from the WPA may be instrumental in inducing a biennial modulation to natural ENSO cycles. The causes of the 1997 and 1998 rainfall anomalies over the ASM subregions are discussed in the context of these results and in light of recent observations of long-term changes in the monsoon-ENSO relationship.

Lau, K. M. and S. Yang (1996). "The Asian monsoon and predictability of the tropical ocean-atmosphere system." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 122(532): 945-957.

The influence of the Asian monsoon on the predictability of the tropical ocean-atmosphere is studied using long-term records of monsoon rainfall, sea-level pressure, sea surface temperature (SST) and surface wind data. Results indicate that the Asian monsoon plays an important role in mediating interannual variations of SST, surface pressure and surface wind in a quasi-biennial oscillation of the tropical ocean-atmosphere as found in previous studies. During the boreal spring, monsoon-related atmospheric and oceanic anomalies change most rapidly, while the east-west gradients in sea-level pressure and SST across the equatorial Pacific are at a minimum. The so-called `spring predictability barrier' (SPB) is associated with the phase-locking of interannual anomalies to the annual cycle variation of the tropical ocean-atmosphere. Results suggest that the Asian monsoon defines two climatic states in the tropical ocean-atmosphere system, corresponding to the warm and cold phases of the tropical biennial oscillation. A weak Asian monsoon is associated with enhanced memory for predictions starting from late boreal spring through to summer and with a well-defined SPB for those starting from boreal fall to winter. On the other hand, a strong monsoon is associated with a recovery of memory at long lags (>4-6 months) from the boreal fall through to the following spring, indicating a partial breakdown or `tunnelling' effect for the SPB. The above results may be exploited to improve seasonal-to-interannual predictions of the monsoon-ocean-atmosphere system.

Lau, K. M. and S. Yang (1997). "Climatology and interannual variability of the Southeast Asian summer monsoon." Advances in Atmospheric Sciences, Beijing, China 14(2): 141-162.

In this paper, results from a pilot study for the South China Sea Monsoon Experiment are reported. Based on analyses of 9 years of pentad and monthly mean data, the climatology of subseasonal features and interannual variability of the Southeast Asian monsoon (SEAM) are documented. The present analysis is focused on the sudden onset of the South China Sea monsoon and its relation to the atmospheric and oceanic processes on the entire Asian monsoon region. It is found that the onset of the SEAM occurs around mid-May signaling the earliest stage of the entire Asian summer monsoon system. The establishment of monsoon rainfall over the South China Sea is abrupt, being accompanied by substantial changes in the large scale atmospheric circulation and sea surface temperature in the adjacent oceans. The onset and fluctuations of SEAM involve the interaction and metamorphosis of the large scale convection over the Indo-China, the South China Sea and the southern Bay of Bengal. Results show that the onset time of the SEAM differs greatly from one year to another. The delayed (advanced) onset of the monsoon may be related to basin-wide warm (cold) events of the Pacific and Indian Oceans. We also present evidence showing that the SEAM fluctuations in May may foreshadow the development of the full-scale Asian summer monsoon during the subsequent months.

Laval, K., R. Raghava, et al. (1996). "Simulations of the 1987 and 1988 Indian monsoons using the LMD GCM." Journal of Climate, Boston, MA 9(12, Pt. II): 3357-3371.

Results from 90-day simulations with the LMD GCM are described, where sea surface temperatures of 1987 or 1988 years are respectively prescribed. The initial states correspond to 1 June 1987 and 1 June 1988. The simulated precipitation rates over India show a strong contrast between the two years, with drought occurring during summer 1987 and abundant rainfall during summer 1988. The dry regime simulated during 1987 corresponds to an eastward displacement of the outflow at 200 mb and a weaker westerly flow at the surface as compared with 1988, both features being in agreement with reality. Because it is more difficult for models to simulate rainfall differences than to simulate wind variations between the two years, the changes in simulated rainfall over India are studied in more detail. In particular, more integrations are carried out to test the sensitivity of rainfall variations to initial conditions, and the result is that the decrease of rainfall in 1987 compared to 1988 is a robust feature of the model. Very early, the importance of evapotranspiration in simulating land rainfall was emphasized. Additional integrations are performed in order to study the impact of the new vegetation scheme introduced in the LMD GCM. It is shown that the contrast in rainfall between the two years is better simulated when the evapotranspiration rate of vegetation cover is represented. When vegetation is not represented in the model, the model does not simulate accurately the interannual variation of the precipitation rates.

Lawrence, D. M. and P. J. Webster (2001). "Interannual Variations of the Intraseasonal Oscillation in the South Asian Summer Monsoon Region." Journal of Climate 14(13): 2910-2922.

It is noted that the behavior of the intraseasonal oscillation (ISO) of the south Asian monsoon varies from year to year. An index representing seasonally averaged ISO activity is developed using outgoing longwave radiation data for the period 1975-97. Interannual variations in ISO activity are found to be related to year-to-year changes in the number of discrete events rather than to changes in the characteristic period. Summertime ISO activity exhibits a reasonably strong inverse relationship with Indian monsoon strength but not with total south Asian monsoon strength primarily because of a lack of correlation between ISO activity and the Bay of Bengal component of the south Asian monsoon. Over the 22-yr period examined here, the relationship between Indian monsoon strength and ISO activity is comparable to or even stronger than the well-documented relationship with El Nino-Southern Oscillation (ENSO). However, summertime ISO activity is found to be relatively uncorrelated with ENSO except for a weakly positive correlation at the beginning of the south Asian monsoon season. Therefore, the ISO activity-Indian monsoon relationship is essentially independent of the ENSO-Indian monsoon relationship. ISO activity is uncorrelated with any other contemporaneous or leading sea surface temperature variability.

Lee, T. and J. Marotzke (1998). "Seasonal cycles of meridional overturning and heat transport of the Indian Ocean." Journal of Physical Oceanography, Boston, MA 28(5): 923-943.

A general circulation model of the Indian Ocean is fitted to monthly averaged climatological temperatures, salinities, and surface fluxes using the adjoint method. Interannual variability is minimized by penalizing the temporal drift from one seasonal cycle to another during a two-year integration. The resultant meridional over-turning and heat transport display large seasonal variations, with maximum amplitudes of 18 and 22 ( x 10 super(6) m super(3) s super(-) super(1) ) for the overturning and 1.8 and 1.4 ( x 10 super(1) super(5) W) for heat transport near 10 degrees S and 10 degrees N, respectively. A dynamical decomposition of the overturning and heat transport shows that the time-varying Ekman flow plus its barotropic compensation can explain a large part of the seasonal variations in overturning and heat transport. The maximum variations at 10 degrees N and 10 degrees S are associated with monsoon reversal over the northern Indian Ocean and changes of the easterlies over the southern Indian Ocean. An external mode with variable topography has a moderate contribution where the Somali Current and the corresponding gyre reverse direction seasonally. Contribution from vertical shear (thermal wind and ageostrophic shear) is dominant near the southern boundary and large near the Somali Current latitudes. The dominant balance in the zonally integrated heat budget is between heat storage change and heat transport convergence except south of 15 degrees S. Optimization with seasonal forcings improves estimates of sea surface temperatures, but the annual average overturning and heat transport are very similar to previous results with annual mean forcings. The annual average heat transport consists of roughly equal contributions from time-mean and time-varying fields of meridional velocities and temperatures in the northern Indian Ocean, indicating a significant rectification to the heat transport due to the time-varying fields. The time-mean and time-varying contributions are primarily due to the overturning and horizontal gyre, respectively. Inclusion of TOPEX data enhances the seasonal cycles of the estimated overturning and heat transport in the central Indian Ocean significantly and improves the estimated equatorial zonal flows but leads to unrealistic estimates of the velocity structure near the Indonesian Throughflow region, most likely owing to the deficiencies in the lateral boundary conditions.

Li, C., M. Mu, et al. (1999). "The variation of warm pool in the equatorial western Pacific and its impacts on climate." Advances in Atmospheric Sciences, Beijing, China 16(3): 378-394.

The variation of warm pool ocean temperature in the equatorial western Pacific and its impacts on climatic change are studied in the present paper. The SSTs in the warm pool region not only have seasonal variation but also have interannual variation more clearly; The influence of anomalies of SST in the warm pool region on the East Asian monsoon is studied with data analysis; And the impact of SSTA in the warm pool region on the teleconnection (wave-train) in the atmospheric circulation is still investigated. The influence of ocean temperature anomalies in the warm pool subsurface on the occurrence of ENSO is also discussed by using data analysis and modelling with CGCM. All above-mentioned studies show that the situation of ocean temperature in the warm pool region in the equatorial western Pacific plays an important role in the global climatic variation.

Li, C. and M. Yanai (1996). "The onset and interannual variability of the Asian summer monsoon in relatin to land-sea thermal contrast." Journal of Climate, Boston, MA 9(2): 358-375.

The onset and interannual variability of the Asian summer monsoon in relation to land-sea thermal contrast and its contributing factors are studied using a 14-yr (1979-1992) dataset. The onset of the Asian summer monsoon is concurrent with the reversal of meridional temperature gradient in the upper troposphere south of the Tibetan Plateau. The reversal is the result of large temperature increases in May to June over Eurasia centered on the Plateau with no appreciable temperature change over the Indian Ocean. In spring the Tibetan Plateau is a heat source that is distinctly separate from the heat source associated with the rain belt in the equatorial Indian Ocean. The Tibetan heat source is mainly contributed by sensible heat flux from the ground surface, while the oceanic heat source is due to the release of latent heat of condensation. It is the sensible heating over the Plateau region in spring that leads to the reversal of meridional temperature gradient. Despite its intensity the condensational heating over the Indian Ocean does not result in tropospheric warming because it is offset by the adiabatic cooling of ascending air. A monsoon intensity index, based on the magnitude of the summer mean vertical shear of zonal wind over the North Indian Ocean, is used to compare the years of strong and weak Asian summer monsoon circulation. The strong (weak) Asian summer monsoon years are associated with (a) positive (negative) tropospheric temperature anomalies over Eurasia, but negative (positive) temperature anomalies over the Indian Ocean and the eastern Pacific; (b) negative (positive) SST anomalies in the equatorial eastern Pacific, Arabian Sea, Bay of Bengal, and South China Sea, but positive (negative) SST anomalies in the equatorial western Pacific; and (c) strong (weak) heating and cumulus convection over the Asian monsoon region and the western Pacific, but weaker (stronger) heating and convection in the equatorial Pacific.

Li, G.-q. (1982). "Some correlation phenomena of the low-latitude circulation over the Asian summer monsoon area and the Southern Hemisphere." Scientia Atmospherica Sinica, Peking 6(1): 95-102.

In this paper, synoptic and climatic analyses for the low-latitude circulation over the Asian summer monsoon area and some areas in the Southern Hemisphere were made by using reference data. According to the analysis of surface air pressure data, a correlation of interannual variation of the monthly averaged July surface air pressure among some stations in Southeast Asia, Australia, India, the Southwest Pacific Ocean, the Indian Ocean, and East Africa was found. The monthly and five-day-period satellite images from April to July, 1975, were made to analyze the development of the summer monsoon process. An abrupt change was found in the main circulation systems of Asia during the monsoon onset. In addition, the variation of 10-day-period mean cloudiness in Asian summer monsoon areas M sub(1) (65-75 degrees E, 30 degrees S-30 degrees N) and M sub(2) (105-115 degrees E, 30 degrees S-30 degrees N) and in Pacific Ocean area ``T'' (145-155 degrees E, 30 degrees S-30 degrees N) was investigated. There was a good correlation in the cloudiness variations in the Southern and Northern Hemisphere areas of M sub(1) and M sub(2) , whereas for ``T,'' which is located in the Pacific Ocean far from any continent, such correlation was absent. Analysis of other data shows that there is better correlation in large-scale circulation between the Northern Hemisphere and the Southern Hemisphere in monsoon longitudes than in nonmonsoon longitudes.

Li, M., Y. Wu, et al. (1987). "Relationship between the monsoon rainfall over eastern China and the Eastern Equatorial Pacific sea surface temperature." Scientia Atmospherica Sinica, Beijing 11(4): 365-372.

The relation between the abnormal monsoon rainfall over China and the Pacific sea surface temperature (SST) departures is examined. The authors are specifically concerned with the interannual variability of monthly means for the Northern Hemisphere during the summers of 1951-1975. The correlations between the time series of the first empirical orthogonal function (EOF) of the Eastern Equatorial Pacific SST departures and the monsoon rainfall over the Yangtze River and the Pacific subtropical high index exhibit a well-defined teleconnection pattern. It is found that the drought (flood) over the Yangtze River corresponds to the warming (cooling) in the Eastern Equatorial Pacific and the cooling (warming) in the West Pacific. Corresponding to these two planetary patterns of Pacific SST departures, there are two abnormal monsoon circulation patterns: one is similar to the wave trains shown by Horel and Wallace (1982) in the winter during an equatorial warm episode, and the other has opposite signs of departure centers in similar locations, but the intensity is weaker than in the former case. The SST departures in the East Pacific change the intensity and location of the West Pacific subtropical high, with subsequent effects on the cross-equatorial flow over an Indonesian area, the low-level southeast monsoon over eastern China, and the rainfall over the Yangtze River. A three-dimensional planetary convective cell is proposed to interpret the global abnormal monsoon circulation, based on the surface temperature contrast between the middle Equatorial Pacific and the West Pacific (or Eastern Asia).

Li, P. (1995). "Comments on ``An apparent relationship between Himalyan snow cover and summer monsoon rainfall over India''." Acta Meteorologica Sinica, Beijing, China 9(3): 360-367.

The snow cover in central High Asia has been the focus of climatologists interests for many decades. Earlier studies indicate that Himalayan snow cover has a significant effect on Indian monsoon rainfall, but it has relied on very limited snow cover data. In this paper, three complete High Asian snow cover data sets are used. They consist of SMMR pentad snow depth maps covering the period 1978-1987, operational NOAA weekly snow cover extent charts during the period between 1966-1989, and daily snow depth records at 60 primary weather stations over the 36-year period of 1957-1992. Unpervasive feature, dearth of snow mass in the vast interior, and limited portion affected by substantial interannual variability reveal that the High Asian snow cover itself could not greatly influence the Indian monsoon rainfall. A simple approach of lead/lag relation between High Asian snow cover, Indian monsoon rainfall, and ENSO shows that snow cover is not a key variable influencing the Indian monsoon. Further correlation calculation demonstrated that only a weak signal was found between them.

Li, T., C. W. Tham, et al. (2001). "A coupled air-sea-monsoon oscillator for the tropospheric biennial oscillation." Journal of Climate, Boston, MA 14(5): 752-764.

The cause of the tropospheric biennial oscillation (TBO) in a simple coupled ocean-atmosphere model is examined. The model is first reduced to a pair of coupled linear first-order differential equations, piecewise in time, for analysis. It is found that two ingredients are essential for the biennial oscillation in the model. The first ingredient is the amplification of SST perturbations in both the Indian Ocean and western Pacific in opposite directions during the northern autumn, winter, and spring seasons, reflecting a positive feedback process. The second ingredient is the decay and change of signs of the SST anomaly in the western Pacific during the northern summer, representing a negative feedback process. Under such a scenario, the simple model exhibits a regular biennial oscillation. Diagnosis of the model TBO reveals that the western Pacific SST and zonal wind anomalies have a lagged correlation at a timescale of 2-3 months, similar to observations. Such a phase lag results from both remote and local ocean-atmosphere-land interaction processes. The remote processes involve the large-scale east-west circulation associated with anomalous monsoon heating, whereas the local processes include the ocean horizontal and vertical advection and surface wind-evaporation-SST feedback. It is concluded that the phase lag between the SST and wind is a result rather than a cause of the TBO. Oscillatory and nonoscillatory regimes of the model's solutions are obtained with the tuning of key parameters within realistic ranges. It is found that the model TBO is sensitive to both internal air-sea coupling coefficients and external basic-state parameters. With the slight change of these parameters, the model may undergo a bifurcation from a TBO regime to a chaotic regime or an annual oscillation regime--a possible scenario for the TBO irregularity. In particular, with a specification of interdecadal change of the basic-state wind, the model may undergo a continuous warming pattern in the eastern Pacific, resembling the prolonged El Nino condition in the early 1990s.

Lian, Y., G. An, et al. (1997). "Variations of temperature and precipitation during the last forty years in Jilin Province." Quarterly Journal of Applied Meteorology, Beijing, China 8(2): 197-204.

Using data set of ten representative stations in Jilin Province for 40 years and the power spectral method, the seasonal variations of precipitation and temperature were analyesed, respectively. The results show that the period of a short-term climatic change in Jilin is almost consistent with that of the interannual oscillation of quasi-3. 5-year (QTO) and quasi-biennial (QBO) of East Asia monsoon. Furthermore, it is found that the seasonal temperature got warm clearly about 2 C higher than that of the 1950s in winter, but weakly in summer. As compared with the low temperature period in summer from the 1950s to the 1970s, the temperature was a relative warm during the period of 1980s. Also, progression or retrogression of subtropical summer monsoon has a great effect in the temperature and precipitation of the summer in Jilin.

Liang, X.-Z., A. N. Samel, et al. (1995). "Observed and GCM simulated decadal variability of monsoon rainfall in east China." Climate Dynamics, Berlin, Germany 11(2): 103-114.

Variability and associated mechanisms of summer rainfall over east China are identified and described using both observations and a general circulation model (GCM) simulation. The observations include two data sets: the 90-station, 1470-1988 annual drought /flood index and the 60-station, 1889-1988 monthly mean precipitation measurements. The GCM data set is a 100-year equilibrium simulation of the present climate. Spectra of the drought/flood index indicate decadal cycles which decrease from north ( similar to 47 y) to south ( similar to 21 y). Correlation coefficients show decadal variability in the relationship between index values along the Yangtse River valley and those over northeast and southeast China. Analysis of the measured data confirms this result; for example, the correlation was small during 1889-1918, but significantly negative during 1930-1959. When compared with precipitation measurements, the GCM better simulates monthly means and variances along the Yangtse River valley. Three distinct 30-year periods of interannual variability in summer rainfall are found over this area. During each period, rainfall is negatively correlated with spring surface temperature over a remote region and is identified with variations in a specific component of the east Asian monsoon circulation: (1) when Eurasian temperatures decrease, the thermal contrast across the Mei-Yu front increases and frontal rainfall intensities; (2) lower temperatures over the Sea of Japan /northwest Pacific Ocean are identified with enhanced easterly flow, moisture transport and rainfall; (3) when tropical east Pacific Ocean temperatures decrease, rainfall associated with the low latitude monsoon trough increases. Given that the GCM generates decadal changes in the relationship between the physical mechanisms, the east Asian monsoon and planetary general circulations and east China rainfall, future studies should focus on the predictability of these changes with the use of improved and much longer GCM simulations.

Liang, X.-Z. and W.-C. Wang (1998). "Associations between China monsoon rainfall and tropospheric jets." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 124(552): 2597-2623.

Strong associations, in both the annual cycle and interannual variations, between east China monsoon rainfall and tropospheric jets are established with the use of observations and general-circulation model simulations. Two distinct systems dominate regional rainfall: the east Asian jet stream (EAJ) in the north and the Hadley cell in the south. The EAJ is associated with Mei-Yu and polar fronts as well as vigorous jet-transverse circulations, whereas the Hadley cell is allied to tropical upper-level easterlies and intertropical convergence zone convection. An equatorward EAJ displacement causes precipitation to increase over south-central (south) China during June-August (January-March). Conversely, a poleward shift of the summer (winter) EJ brings heavier precipitation over north (central-north) China. On the other hand, over the South China Sea the Hadley cell influence prevails and, consequently, increased rainfalls concur with enhanced lower-level westerlies. Furthermore, the EAJ fluctuations are strongly coupled with southern oscillation variations. Their interactions tend to precede (follow) El Nino phenomena during October through May (summer). The EAJ related flow anomalies also have potential skill to predict China rainfall interannual variability. To conclude, a realistic China monsoon simulation requires accurate representation of the EAJ and Hadley cell. Both features link regional rainfall to tropical and extratropical planetary-scale circulations and, in turn, to global surface characteristics.

Liebmann, B. and D. L. Hartmann (1984). "Observational study of tropical-midlatitude interaction on intraseasonal time scales during winter." Journal of the Atmospheric Sciences, Boston 41(23): 3333-3350.

Eight Northern Hemisphere winters of five- and ten-day average midlatitude 500-mb heights and tropical outgoing IR are used in a correlative study of tropical-midlatitude interaction. The seasonal cycle and interannual variability are removed so that only intraseasonal variability remains. Results indicate that energy predominantly propagates from midlatitudes to the Tropics for both five- and ten-day-averaged data, although the propagation is more apparent in five-day-averaged data. This is because the largest tropical IR patterns are southeastward of the 500-mb point with which the IR field is correlated. The result is interpreted in terms of a quasi-stationary Rossby wave that has an eastward component of group velocity. The SW-NE tilt of the 500-mb height correlation patterns, indicating poleward momentum transport or equatorward wave propagation, also supports the hypothesis that midlatitude flow drives the Tropics. Lead and lag correlations show that, when 500-mb heights lead IR, an upstream development appears in the 500-mb correlation pattern. The field is nearly featureless, however, when 500-mb heights lag IR. Well-defined time evolution is more evident over the eastern Pacific than over the western Pacific. The only indication of possible forcing of the midlatitude flow by the Tropics is from IR anomalies in the region of winter monsoon rainfall over the far western Pacific, which are associated with a pattern of correlations in the 500-mb field of nearly global extent. The pattern may be related to that produced by Simmons et al. with a barotropic model, when steady forcing is used to perturb a zonally varying basic state. Simmons et al. hypothesize that the large global anomalies are the result of the barotropic instability of the basic state. Although the global correlation pattern is statistically significant, it explains only a small fraction of the total variance.

Limsakul, A., T. Saino, et al. (2001). "Temporal variations in lower trophic level biological environments in the northwestern North Pacific Subtropical Gyre from 1950 to 1997." Progress in Oceanography 49(1-4): 129-149.

An examination of large archives (1950-1997) of the oceanographic and atmospheric data from the northwestern North Pacific Subtropical Gyre has revealed clear linkages between atmospheric forcing factors, physical processes and biological events. Large changes in the winter and spring biomass of phytoplankton and macroplankton observed over annual, decadal and inter-decadal time scales could clearly be attributed to climate-related changes in oceanographic processes. Interannual changes in the intensity of the winter-time East Asian Monsoon had a significant impact on the extent of convective overturning, on nitrate inputs into the euphotic zone and the concentrations of chlorophyll a in winter and during the following spring. A prolonged period of deeper winter mixed layers observed from the mid-1970s to the mid-1980s led to a sizeable increase in winter mixed-layer nitrate concentrations. This change resulted in a decrease in winter-time phytoplankton biomass. Spring-time chlorophyll a, in contrast, showed a steady increase during this period. The decline in winter phytoplankton biomass could be attributed to the depths of mixed layer. A deeper mixed layer prevents phytoplankton from remaining in the euphotic zone for long enough to photosynthesize and grow, leaving substantial amounts of nutrients unutilised. However, as a result of stratification of the water column in spring following each of these winters, phytoplankton could take advantage of the enhanced ambient concentrations of nutrients and increase its biomass. Another noteworthy observation for the period from the mid-1970s to the early 1980s is that the western subtropical gyre progressively became phosphate limited. The period of diminishing mixed-layer phosphate concentrations was observed in our study area from the early 1990s onwards was consistent with recent observations at Station ALOHA in the eastern subtropical gyre.

Liu, X., S. Li, et al. (2000). "Relationship between the dipole tropical convective activities and East Asian summer monsoon." Journal of Nanjing Institute of Meteorology, Nanjing, China 23(3): 323-329.

In terms of 1979 similar to 1994 NCEP/NCAR re-analyses and OLR data, the variation characteristics of tropical convective activities are investigated and the relationships between the interannual variation of summer OLR and East Asian summer monsoon (EASM) are discussed. It is found that the interannual variation of summer OLR is remarkable in warm pool and the equatorial central Pacific, which is in anti-phase oscillation. When the convective activities are strong (weak) in warm pool and weak (strong) in the equatorial central Pacific, the EASM is strong (weak) and the rainbelt is north (south) of its mean position with less (more) precipitation in the Yangtze River reaches. Further evidences show that the atmospheric circulation anomaly in subtropical Asia (tropical Pacific) relative to the dipole tropical convective activities is vertically barotropic (baroclinic).

Lockwood, J. G. (1984). "Southern Oscillation and El Nino." Progress in Physical Geography, London 8(1): 102-110.

This last decade has witnessed an upsurge of scientific interest in both the Southern Oscillation and El Nino. This is because it has become clear that the Southern Oscillation is associated with major ocean-atmosphere changes throughout the Tropical Pacific Basin and beyond. Barnett (1977) suggests that the observed interannual fluctuations of mean sea surface temperature (SST) in the eastern Tropical Pacific are consistent with a North Equatorial Countercurrent mechanism, as hypothesized by Bjerknes (1961, 1966) and, later, Wyrtki (1973). Barnett considers that observations of SST fluctuations in the Peruvian coastal zone are not consistent with the idea that locally driven upwelling alone plays a significant role in the large-scale interannual variations in heat balance; variations in SST associated with El Ninos are evidently associated with other causes. The flow of warm water south across the equatorial front also has a significant, but limited, effect on the heat budget of the Peruvian coastal stations, so this process cannot account for the major changes observed in SST off Peru. A teleconnection between the Indian monsoon and El Nino is considered.

Lu, E. and J. C. L. Chan (1999). "A unified monsoon index for south China." Journal of Climate, Boston, MA 12(8, Pt. 1): 2375-2385.

A unified index for both the summer and winter monsoons over south China (SC) is proposed for the purpose of studying their interannual variability. By examining the monthly distribution of the meridional flow v over the Asia-Pacific region from 20 yr (1976-95) of the reanalysis data of the National Centers for Environmental Prediction, the area of the South China Sea (SCS) is identified as an important segment of the planetary-scale east Asia monsoon circulation. The monthly v fields at 1000 and 200 hPa over the SCS show the most significant reversal in direction between summer and winter. The summer rainfall over SC is found to correlate well with these two fields as well as their differences averaged over the northern part of the SCS (7.5 degrees -20 degrees N, 107.5 degrees -120 degrees E). Winter temperatures over SC are, however, only related to the v field at 1000 hPa within the same region. It is therefore proposed to define a unified monsoon index for SC as the value of v at 1000 hPa averaged over this region within the period of June through August for summer and November through February for winter.

Lu, J. and Y. Ding (1989). "Medium-range oscillations in the summer tropical easterlies at 200 hPa." Advances in Atmospheric Sciences, Beijing, China 6(3): 301-312.

By the use of space-time spectral analysis and band-pass filter, some of the features of the medium-range oscillations in the summer tropical easterlies (10 degrees S-20 degrees N) at 200 hPa are investigated based on a two-year (1980 and 1982) wind (u, v) data set for the period from May to September. Space-time power spectral analysis shows that the total energy of the westward moving waves was the largest and that of the standing waves and eastward moving waves was relatively small in the 200 hPa easterlies; the total energy of the eastward moving waves at minimum at 10 degrees N. Three kinds of the medium-range oscillations with about 50-day, 25-day and quasi-biweekly periods were found in the easterlies, which all show a remarkable interannual variation and latitudinal differences in these two years. The wave energy of zonal wind is mainly associated with the planetary waves (1-3), which all may make important contributions to the 50-day and 25-day oscillations in different years of different latitudes. The quasi-biweekly oscillations are mainly related to the synoptic waves (4-6). In the equatorial region, the 50-day oscillation was dominant with a eastward phase propagation in 1982 while the dominant oscillation in 1980 was of 25-day period with a westward phase propagation in 1980. Both of these are of the mode of zonal wave number 1. Strong westward 50-day oscillation was found in 10 degrees N-20 degrees N in these two years. Regular propagation of the meridional wind 50-day oscillation were also found in the easterlies. The 50-day and 25-day oscillation of zonal wind all demonstrate southward phase propagation over the region of the South Asia monsoon and northward phase propagation near the international date line, where the climatic mean position of the tropical upper-tropospheric easterly jet and the tropical upper tropospheric trough (TUTT), are respectively.

Lu, R., R. Chan-Su, et al. (2002). "Associations between the Western North Pacific Monsoon and the South China Sea Monsoon." Advances in Atmospheric Sciences 19(1): 12-24.

Based on the interannual variability of convection over the tropical western North Pacific (WNP), a region of 130 degree -160 degree E, 10 degree -20 degree N, a composite analysis is performed on the fields of surface temperature, outgoing longwave radiation and 850 hPa zonal wind. The composite results show that the weaker (stronger) WNP convection is related to the El Nino (La Nina)-pattern sea surface temperature (SST) anomalies in the preceding winter and in spring. A comparison with previous results indicates that a similar spatial and temporal distribution of SST anomalies is also associated with the onsets of both the WNP and South China Sea (SCS) monsoons. The composite results also show that the weaker (stronger) convection over the WNP corresponds to the easterly (westerly) anomalies that extend westward from the WNP into the Bay of Bengal. A numerical experiment by an atmospheric general circulation model shows a similar result. In addition, during weaker (stronger) convection summer, the convection over the WNP and lower-level zonal winds over the SCS exhibit a small (large) extent of seasonal evolution.

Lu, R., J.-H. Oh, et al. (2001). "Associations with the Interannual Variations of Onset and Withdrawal of the Changma." Advances in Atmospheric Sciences 18(6): 1066-1080.

The associations of onset and withdrawal of the rainy season in South Korea (called Changma) have been examined. Composite studies showed that there are significant differences in circulations between extremely early and late onset (or withdrawals) not only over East Asia, but also over remote areas. The in situ significant differences include the upper-level jet over East Asia and the subtropical anticyclone over the western North Pacific at lower levels. The significant remote associations include the Indian monsoon and ENSO. The Indian summer monsoon is related to both onset and withdrawal of the Changma, while ENSO has a significant relation only to onset, but not to withdrawal.

Luo, H. (1995). "Effect of winter monsoon on summer monsoon through air-sea interaction." Acta Meteorologica Sinica, Beijing, China 9(1): 26-34.

In this paper the relationships between the sea surface temperature (SST) of Xisha and that in the northern Indian and northern Pacific oceans, the geopotential height at 500 hPa level of the Northern Hemisphere, and rainfall in China are studied statistically using data in the period of 1961-1992. Results show that in winter, the interannual variation in SST of Xisha describes that for a large oceanic region off the East Asia coast, and is closely related to the activity of East Asia winter monsoon. On the other hand, there exist very high values of autocorrelation of Xisha SST anomaly from December through the following July, but the anomalous condition is hardly correlated to that in the preceding autumn. The winter monsoon related anomalous SST condition in Xisha has a strong tendency to persist through the succeeding summer monsoon season with the same sign. In addition, correlation maps of monthly mean rainfall in China with respect to Xisha SST of the same month show positive correlations with confidence level above 95% to the east of 110 degrees E and to the south of Changjang (Yangtze) River during the months of October through April; the region becomes smaller in May and changes correlation sign in June; the positive correlation region is located in the middle and lower reaches of Changjang River from July to September. The air-sea interaction plays an important role in these processes.

Luo, H. (2000). "The effect of land-sea contrast on interannual variability of the Asian Monsoon." Acta Meteorologica Sinica, Beijing, China 14(2): 200-209.

Values of the net radiative heating (QRT) at the top of atmosphere (TOA) are derived from the satellite-observed outgoing long wave radiation (OLR) and the TOA short wave net irradiance (SHT) for the region of the Tibetan Plateau and surrounding areas (40 degrees S-40 degrees N, 0-180 degrees E) and the period of months from January 1979 to December 1988. The anomalous QRT (QRT A) in relation to the interannual variability of Asian monsoon is discussed. QRT A for the Earth-atmosphere system in the domain may be linked to the thermal contrasts between continents and oceans and between the plateau and surrounding free atmosphere.

Luther, M. E. and J. J. O'Brien (1989). "Modelling the variability in the Somali Current." Nihoul, J. C. J. and Jamart, B. M.

A numerical model of the wind driven circulation in the Indian Ocean is used to study the variability of the circulation on seasonal and interannual time scales. The model is a nonlinear reduced gravity model driven by observed winds. Model simulations use a monthly mean climatology of ships' winds as forcing and the 23 year long monthly mean Cadet and Diehl winds as forcing. The model is very successful in simulating the observed features of the circulation in this region, such as the formation and decay of the two-gyre system in the Somali Current during the southwest monsoon and the formation of the eddies off the coasts of Oman and Yemen. Examination of model statistics from many years of simulation using climatological monthly mean winds shows that the model fields are exactly repeating from one year to the next over most of the basin, even in the highly nonlinear eddies like the great whirl. Exceptions occur in the smaller scale eddies that form in the strong shear zones around the great whirl and in the southern gyre recirculation region, where the flow field exhibits a more chaotic nature, but even these features are nearly repeating from one year to the next. When observed, interannually varying winds are used to drive the model, the variability from year to year increases dramatically. This indicates that interannual variability in the model fields is due solely to variability in the winds and not due to inherent variability in the model physics, as is seen in mid-latitude models of the oceanic general circulation.

Manton, M. J. (1997). "Symposium on climate prediction and predictability: papers presented at the eighth modelling workshop, 12-14 November 1966." Melbourne, Australia, Bureau of Meteorology Research Centre 126.

Numerical modelling forms a substantial component of the activities in all the Bureau of Meteorology Research Centre (BMRC) research groups. The modelling covers spatial scales from the mesoscale to the global, and it includes the ocean as well as the atmosphere. The annual modelling workshop is a forum in which current topics are discussed from both a national and an international perspective. The 1996 workshop (the ``Symposium on Climate Prediction and Predictability'') represented a somewhat different approach from previous years: the sponsorship was broader and the organising committee attempted to provide a sharper focus. The aspects of prediction and predictability that were selected because of their particular relevance were: Simulated climate variability (e.g., AMIP and coupled model experiments) including intraseasonal and interannual variability; Climate predictability studies; Ocean modelling and initialisation of climate predictions; and Coupled model climate prediction. The papers presented here describe recent work in the field of climate prediction and predictability, an area of immense significance and importance to Australia. The presentations and associated discussion helped sharpen the focus of the Australian scientific community in considering our role in the World Climate Research Programme's CLIVAR (Climate Variability and Predictability) initiative. Table of contents include: Seasonal prediction and predictability studies at ECMWF, David Anderson; The globalization of high performance computing and numerical simulation, David Blaskovich; Prediction and predictability studies at the CCCma, G. J. Boer; Climate sensitivity in a GCM--how non-linear is it?, R. A. Colman, S. B. Power and B. J. McAvaney; Cross-validation of statistical seasonal forecasts, Wasyl Drosdowsky; Simulations of Australian climate variability, C. S. Frederiksen; Eddy parameterizations and systematic kinetic enery errors in atmospheric circulation models, Jorgen S. Fredericsen; Effect of oceanic eddy physics on simulation of global warming, Anthony C. Hirst; Multi-seasonal hindcasts for 1972-1992, B. G. Hunt; Simulating the climate of the 20th century, David Karoly, David Sexton, Chris Folland and David Rowell; Limitations to the predictability of ENSO, Richard Kleeman and Andrew M. Moore; Lessons for climate prediction from rainfall variations over the past century, Ants Leetmaa; A theory for the Southern Hemisphere monsoon: implications for predictability, John McBride and Jun-Ichi Yao; Large scale variability of the southern tropical Indian Ocean, Gary Meyers and Yukio Masumoto; Skill assessment for ENSO using ensemble prediction, Andrew M. Moore and Richard Kleeman; Impact on the Australian-Pacific region of the ENSO signal in a global coupled GCM, S. P. O'Farrell; A coupled general circulation model for seasonal prediction and climate change research, S. Power, F. Tseitkin, R. Colman, B. McAvaney, J. Fraser, R. Kleeman and A. Sulaiman; Modelling studies of the Australian and Indian monsoons, K. Puri and R. Colman; The annual cycle, climate drift and ENSO forecasting, A. Rosati; A numerical simulation of water pathways between the subtropical and tropical Pacific Ocean: implications for ENSO prediction, Lewis M. Rothstein; Assessing atmospheric seasonal predictability using an ensemble of multi-decadal AGCM simulations, David P. Rowell, John R. Davies, Alison C. Renshaw and Chris K. Folland; The Australian climate variability ocean model, A. Schiller, P. McIntosh, G. Meyers and J. S. Godfrey; Prediction and diagnosis of Chinese monsoonal rainfall from conditions in the Philippines warm pool, Ian Simmonds and Daohua Bi; Prediction and predictability: some implications for observing system design, Neville R. Smith; Dynamical climate predictions at the Japan Meteorological Agency, Kiyoharu Takano; Predictions of global warming using a simple energy balance model, Ian G. Watterson; The climate response to the instantaneous removal o

Manton, M. J. and J. L. McBride (1992). "Recent research on the Australian monsoon." Journal of the Meteorological Society of Japan, Tokyo, Japan 70(1B): 275-285.

Owing to the data flowing from a number of observational programs, there has been over the last few years a sustained research effort on improving our understanding of the Australian monsoon. This paper discusses the findings of that research, including results on the large-scale structure of the monsoon, interannual variability, onset, intraseasonal variability, and mesoscale structure. Although there has been significant progress, much work remains to be done on relating regional aspects of the monsoon to the general tropical circulation.

Marengo, J. A., I. F. De Albuquerque Cavalcanti, et al. (2001). "Ensemble simulation of interanual climate variability using the CPTEC/COLA atmospheric model." Publicacao. Instituto Nacional de Pesquisas Espaciais [Publ. Inst. Nac. Pesqui. Espac.]. no. 8135: 1-77.

The interannual climate variability of the CPTEC/COLA Atmospheric GCM is assessed for several regions of the tropics and extratropics. The evaluation is made for the period 1982-91 for an ensemble run of 9 realizations of the model forced by observed global sea surface temperature (SST) anomalies. The Brier Skill Score is used to assess the precipitation simulated by the model for several regions of South America, Africa and Asia during the peak of their rainy seasons. Interannual climate variability in Northeast Brazil, Amazonia, and southern Argentina-Uruguay and to a lesser degree for Sahel and Eastern Africa rainfall are well simulated by the model. The model exhibits lower skill in reproducing interannual rainfall variability in the monsoon regions of world and southern Africa, indicating that simulation on interannual variations of climate in those regions still remains problematic, possibly due to the effect of land-surface moisture and snow feedbacks that would indicate the important role of internal climate variability in those regions, besides the SST external forcing. The model captures the well known signatures of rainfall and circulation anomalies of El Nino 1982-83, indicating its sensitivity to strong external forcing, while in normal years, the internal climate variability can affect the predictability of climate in some regions, especially the monsoon areas of the world.Original Abstract: A variabilidade climatica interanual do MCG atmosferico do CPTEC/COLA e avaliada para diversas regioes dos tropicos e extratropicos. A avaliacao foi feita para o periodo 1982-91 com uma rodada de 9 membros do modelo forcado pelas anomalias de temperatura da superficie (TSM) do mar observadas de todo o globo. O Brier Skill Score e usado para avaliar a precipitacao simulada pelo modelo para diversas regioes da America do Sul, Africa e Asia durante o pico de suas estacoes chuvosas. A variabilidade climatica interanual no Nordeste do Brasil, Amazonia, e sul da Argentina-Uruguai e em menor grau para a precipitacao para o Sahel e leste da Africa foram bem simuladas pelo modelo. O modelo exibe menor skill quando reproduz a variabilidade interanual da precipitacao nas regioes das moncoes do globo e sul da Africa, indicando que a simulacao das variacoes interanuais do clima nestas regioes ainda sao problematicas, possivelmente devido ao efeito de feedback da umidade do solo e da neve, que indicaria o importante papel da variabilidade climatica interna nestas regioes, alem da forcante externa SST na variabilidade climatica. O modelo captura bem os conhecidos sinais das anomalias de precipitacao e circulacao do El Nino de 1982-83, indicando sua sensibilidade a uma forte forcante externa, enquanto que em anos normais, a variabilidade climatica interna pode afetar a previsibilidade do clima em algumas regioes, especialmente as areas de moncoes do globo.

Martin, G. M. (1999). "The simulation of the Asian summer monsoon, and its sensitivity to horizontal resolution, in the UK Meteorological Office Unified Model." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 125(557, Pt. A): 1499-1525.

The quality of the simulation of the Asian summer monsoon in the climate version of the UK Meteorological Office's United Model, and the impact upon this of increased horizontal resolution, is investigated using two atmosphere-only model runs forced with observed sea surface temperatures (SSTs) and sea ice extents. The runs each cover the period from 1979 to 1988, but have different horizontal resolutions, with one at climate resolution (2.5 degrees latitude by 3.75 degrees longitude, about 300 km at midlatitudes) and the other at global forecast model resolution (0.833 degrees latitude by 1.25 degrees longitude, approximately 100 km at midlatitudes). The characteristic monsoon circulation and the spatial distribution of precipitation are in good agreement with observations. However, the model has a tendency to overestimate the strength of the monsoon, and also exhibits an early monsoon onset. The large-scale interannual variations in circulation appear to be simulated reasonably well (as far as can be determined using this short dataset), although the magnitude of the interannual variability of precipitation is overestimated. However, the regional circulation and precipitation changes between El Nino and La Nina years show some significant differences between the model and the observations. The dominant mode of intraseasonal variability seen in both model simulations is, in agreement with observations, associated with the active/break cycle of the monsoon (although this only explains about 10% of the total variance in both simulations). There is some evidence that the SST changes associated with El Nino may produce a coherent forcing of the secondary (east-west) mode of intraseasonal variability during the onset phase of the monsoon in the model. However, comparison with observations suggests that this may not be representative of what occurs in the real atmosphere. There is no evidence that the SST variations are causing the system to prefer either the active or the break monsoon phase, as was suggested by Palmer. With increased model horizontal resolution, extra detail is provided in the precipitation distribution, but the mean monsoon simulation is scarcely altered and the systematic errors remain. The interannual variations in circulation and precipitation appear not to be greatly altered, and the overall pattern of intraseasonal variability is also unaffected. This study suggests that the systematic errors in the monsoon simulation are not a result of poor horizontal resolution, but may be due to problems with the model physics.

Matsuyama, H. and K. Masuda (1998). "Seasonal/interannual variations of soil moisture in the former USSR and its relationship to Indian summer monsoon rainfall." Journal of Climate, Boston, MA 11(4): 652-658.

Seasonal/interannual variations of soil moisture in the former USSR during the period from 1972 to 1985 are investigated by using in situ data. An index of soil moisture in central Eurasia is evaluated as the arithmetic mean of soil moisture normalized by the respective field capacity. This index exhibits a maximum at the end of April when the interannual variability of the index reaches a yearly minimum. It was found that snowmelt occurring around mid-April is responsible for this feature, which results in the least persistence of this index from March to April. Using this index, the relationships between land surface processes over central Eurasia and the following Indian summer monsoons are investigated from the viewpoint of the snow-hydrological effect. The seasonal march of this index and that of spatially averaged snow depth in central Eurasia are described. Based on the amount of Indian summer monsoon rainfall, two cases of good and two cases of poor monsoon years are selected. During these years, an apparent inverse relationship is found between April snow cover over central Eurasia and the subsequent Indian summer monsoon rainfall. Results indicate that during the warm phases of ENSO, the snow-hydrological effect does not hold, whereas it holds during other years. This result does not contradict former observational and modeling studies, and implies that variations in Indian summer monsoon rainfall are most strongly related to the anomalous circulation of the coupled ocean-atmosphere system, with some contribution from the snow-hydrological effect.

McBride, J. (1998). "Indonesia, Papua New Guinea and tropical Australia: the Southern Hemisphere monsoon." Karoly, David J. and Vincent, Dayton G.

The meteorology of the region is described briefly in the context of traditional monsoon meteorology. Various studies are summarized concerning the morphology of monsoon onset and retreat, as well as active and break patterns. The major emphasis of this chapter is on the role of the Indonesian-Australian region in global dynamics. As noted originally by Ramage (1968), during the southern summer the major global tropical heat source is located over this region; for this reason, the region is referred to as the maritime continent. The associated latent heat release can be considered, from energetic considerations, to be the forcing mechanism for the observed large-scale circulation of the global Tropics. The role of the region is also described in the global meridional circulation of mass between the troposphere and the stratosphere. The water vapor budget of the stratosphere is such that it must be dried through mechanisms involving overshoot of deep tropical cumulonimbus cells. Analysis of data from field experiments directed at this problem suggest that, once again, the major location for dehydration of the global stratosphere may be the maritime continent during the Southern Hemisphere summer. This chapter also briefly summarizes some aspects of the Indonesian throughflow phenomenon. This is a transport of water from the Pacific Ocean to the Indian Ocean through the seas and channels in the maritime continent region. The throughflow is believed to play a major role in global climate, as the associated net heat transport is a substantial fraction of the total heat absorbed by the Pacific Ocean. Consequently, seasonal and interannual variations in throughflow can have a major influence on large-scale climate.

Meehl, G. A. (1987). "Annual cycle and interannual variability in the tropical Pacific and Indian Ocean regions." Monthly Weather Review, Boston 115(1): 27-50.

The annual cycle of outgoing long-wave radiation (OLR), clouds, precipitation, and sea level pressure is studied from satellite and station data in the tropical Indian and Pacific sectors. A region of heavy convection, termed the tropical convective maximum, moves from north to south and west to east in the Indian and Pacific sectors as the mean annual cycle proceeds from northern summer to northern winter. During its return excursion northwestward from northern winter to northern summer in the Indian sector, it is not as strong as in the preceding half of the annual cycle. To study interannual fluctuations of the annual cycle in these regions, Indian monsoon rainfall is chosen as an indicator of precipitation and convection in the summer monsoon region. Relatively strong and weak years of monsoon rainfall are selected and used as a starting point to follow the evolution of the annual cycle in the two sets of years. More than two-thirds of the monsoon seasons since 1900 are classified as either relatively strong or weak, indicative of the biennial tendency of monsoon rainfall. Examination of sea level pressure, precipitation, and sea surface temperatures shows the dynamically coupled ocean-atmosphere system in the Indian-Pacific region to be involved with producing Southern Oscillation-type signals in atmosphere and ocean in these sets of years, with extremes in the system being manifested as warm and cold events. This is associated with the alternate strengthening and weakening of the mean west-to-east exchange of mass from the Indian to Pacific sectors in the atmosphere, and the interactive response of the ocean in helping reinforce and maintain those anomalies. For example, a year with a relatively strong Indian monsoon is characterized by lower pressure, warmer SSTs, and greater precipitation to the west of the South Pacific Convergence Zone (SPCZ), ahead of the convective maximum as it moves southeastward with the seasonal cycle from northern summer to northern winter. At the same time, higher pressure, decreased precipitation, and low SSTs are in evidence to the east of the SPCZ in the tropical Pacific. In the extratropics, a weakened circumpolar trough in the Southern Hemisphere midlatitudes during May-July, south of New Zealand and southwest of Australia, is associated with strong subtropical highs in the Indian and Pacific oceans. A relatively weak year is characterized by opposite conditions through the course of the annual cycle. A transition from strong to weak is made in northern spring, as low SLP and warm SST in the SPCZ area are associated with westerly wind anomalies in the equatorial western Pacific and a weakened South Pacific High. Warm SSTs then become established in the tropical eastern Pacific as a result of the dynamic response of the ocean, and a weak year begins. Since the system is not purely biennial, such transitions do not occur every year. Extremes in this oscillation, the warm and cold events associated with the Southern Oscillation, occur less frequently, and the anomaly patterns are of much greater amplitude than strong and weak years without warm and cold events. Similar, although weaker, patterns are still in evidence throughout the composite annual cycles of these other years. These results point out that processes in the Indian-Pacific region are continually evolving from one annual cycle to the next and that warm and cold events are not discrete occurrences, but are extremes of patterns that appear in many other years as part of the dynamically coupled air-sea system in this region.

Meehl, G. A. (1988). "Tropical-midlatitude interactions in the Indian and Pacific sectors of the Southern Hemisphere." Monthly Weather Review, Boston 116(3): 472-484.

Observations and three general circulation model (GCM) simulations are analyzed to study interannual processes and interactions involved in the tropical Indian and Pacific sectors and higher southern latitudes. Major features involving the observed eastward progression of the tropical convective maximum, from the Indian monsoon in northern summer to the Australian monsoon and Pacific in southern summer, are represented in all three model simulations. This suggests that the distribution of land and sea accounts for the observed seasonal position of the convective maximum in these regions. However, the South Pacific convergence zone (SPCZ) is not present at any time of year in the slab-ocean models because of the anomalously warm sea-surface temperatures simulated in the equatorial Pacific. Analyses of observed zonal, mean 500-mb temperatures and sea-level pressure, from 10 to 80 degrees S, for warm-event composites minus cold-event composites (representing two extremes of interannual variation) show the period of anomalies at high southern latitudes to be about half a year out of phase with the Tropics. Poleward migration of observed anomalies is most apparent in the Pacific sector, suggesting a delayed communication between the Tropics and high latitudes. A tentative physical explanation is postulated that involves the SPCZ as a conduit for communicating tropical anomalies to higher southern latitudes by changes in the dynamically coupled, ocean-atmosphere system operating in the Tropics and midlatitudes of the Pacific. If such processes are taking place in the real climate system, the Tropics and high southern latitudes are not in equilibrium, and immediate transmission of tropical anomalies to high southern latitudes may not occur. The GCM simulations under consideration, which are run to near-equilibrium, therefore, are not capable of portraying such features of observed interannual variability. These conclusions point to the necessity of using a coupled ocean-atmosphere GCM capable of simulating realistic air-sea interactions to study such interannual and latitudinal linkages in the Indian and Pacific sectors of the Southern Hemisphere.

Meehl, G. A. (1989). "Coupled ocean-atmosphere modelling problem in the tropical Pacific and Asian monsoon regions." Journal of Climate, Boston 2(10): 1146-1163.

Two ocean formulations, one a simple, 50-m slab ocean and another a coarse-resolution global ocean general circulation model (GCM), are coupled to a global atmospheric GCM. To determine what part of the simulation error is introduced by the atmospheric model and what part arises from limitations of the ocean formulation, results are compared to observations as well as to integrations involving the ocean GCM run with observed atmospheric forcing and the atmospheric GCM run with specified observed sea surface temperatures (SSTs). The tropical Indian and Pacific regions are studied because of the associations involving the dynamically coupled ocean-atmosphere system in those regions related to large-scale tropical and global interannual variability. Analysis of the net surface heat flux leads to the conclusion that limitations in the ocean formulations contribute more to errors in the coupled climate simulations than inherent deficiencies in the atmospheric model. In spite of the limitations of the ocean formulations in simulating SST, the atmospheric model simulates most major features associated with the low-level wind fields in the tropical Indian and Pacific regions with differences consistent with the SSTs supplied by the ocean models. The implication is that increased quality of the ocean simulation will result in substantial improvements of the coupled climate model simulations even without upgrades to the atmospheric model. The point is raised that a coupled model with surface fluxes computed interactively produces a more internally consistent climate simulation than could be expected from the same atmospheric model forced with observed SSTs, even if the SSTs computed by the coupled model do not exactly match the observed values. Surface fluxes, then, are not absolute values and must be interpreted as compensatory products of the limitations (and strengths) of the respective media in simulating SST patterns. Thus, even the present generation of imperfect coupled models can provide better insight than other research tools into some of the processes, mechanisms, and sensitivities of the coupled climate system.

Meehl, G. A. (1997). "The south Asian monsoon and the tropospheric biennial oscillation." Journal of Climate, Boston, MA 10(8): 1921-1943.

A mechanism is described that involves the south Asian monsoon as an active part of the tropospheric biennial oscillation (TBO) described in previous studies. This mechanism depends on coupled land-atmosphere-ocean interactions in the Indian sector, large-scale atmospheric east-west circulations in the Tropics, convective heating anomalies over Africa and the Pacific, and tropical-midlatitude interactions in the Northern Hemisphere. A key element for the monsoon role in the TBO is land-sea or meridional tropospheric temperature contrast, with area-averaged surface temperature anomalies over south Asia that are able to persist on a 1-yr timescale without the heat storage characteristics that contribute to this memory mechanism in the ocean. Results from a global coupled general circulation model show that soil moisture anomalies contribute to land-surface temperature anomalies (through latent heat flux anomalies) for only one season after the summer monsoon. A global atmospheric GCM in perpetual January mode is run with observed SSTs with specified convective heating anomalies to demonstrate that convective heating anomalies elsewhere in the Tropics associated with the coupled ocean-atmosphere biennial mechanism can contribute to altering seasonal midlatitude circulation. These changes in the midlatitude longwave pattern, forced by a combination of tropical convective heating anomalies over East Africa, Southeast Asia, and the western Pacific (in association with SST anomalies), are then able to maintain temperature anomalies over south Asia via advection through winter and spring to set up the land-sea meridional tropospheric temperature contrast for the subsequent monsoon. The role of the Indian Ocean, then, is to provide a moisture source and a low-amplitude coupled response component for meridional temperature contrast to help drive the south Asian monsoon. The role of the Pacific is to produce shifts in regionally coupled convection-SST anomalies. These regions are tied together and mutually interact via the large-scale east-west circulation in the atmosphere and contribute to altering midlatitude circulations as well. The coupled model results, and experiments with an atmospheric GCM that includes specified convective heating anomalies, suggest that the influence of south Asian snow cover in the monsoon is not a driving force by itself, but is symptomatic of the large-scale shift in the midlatitude longwave pattern associated with tropical SST and convective heating anomalies.

Meehl, G. A. and J. M. Arblaster (1998). "The Asian-Australian monsoon and El Nino-Southern Oscillation in the NCAR Climate System Model." Journal of Climate, Boston, MA 11(6): 1356-1385.

Features associated with the Asian-Australian monsoon system and El Nino-Southern Oscillation (ENSO) are described in the National Center for Atmospheric Research (NCAR) global coupled Climate System Model (CSM). Simulation characteristics are compared with a version of the atmospheric component of the CSM, the NCAR CCM3 run with time-evolving SSTs from 1950 to 1994, and with observations. The CSM is shown to represent most major features of the monsoon system in terms of mean climatology, interannual variability, and connections to the tropical Pacific. This includes a representation of the Southern Oscillation links between strong Asian-Australian monsoons and associated negative SST anomalies in the eastern equatorial Pacific. The equatorial SST gradient across the Pacific in the CSM is shown to be similar to the observed with somewhat cooler mean SSTs across the entire Pacific by about 1 degrees -2 degrees C. The seasonal cycle of SSTs in the eastern equatorial Pacific has the characteristic signature seen in the observations of relatively warmer SSTs propagating westward in the first half of the year followed by the reestablishment of the cold tongue with relatively colder SSTs propagating westward in the second half of the year. Like other global coupled models, the propagation is similar to the observed but with the establishment of the relatively warmer water in the first half of the year occurring about 1-2 months later than observed. The seasonal cycle of precipitation in the tropical eastern Pacific is also similar to other global coupled models in that there is a tendency for a stronger-than-observed double ITCZ year round, particularly in northern spring, but with a well-produced annual maximum of ITCZ strength north of the equator in the second half of the year. Time series of area-averaged SSTs for the NINO3 region in the eastern equatorial Pacific show that the CSM is producing about 60% of the amplitude of the observed variability in that region, consistent with most other global coupled models. Global correlations between NINO3 time series, global surface temperatures, and sea level pressure (SLP) show that the CSM qualitatively reproduces the major spatial patterns associated with the Southern Oscillation (lower SLP in the central and eastern tropical Pacific when NINO3 SSTs are relatively warmer and higher SLP over the far western Pacific and Indian Oceans, with colder water in the northwest and southwest Pacific). Indices of Asian-Australian monsoon strength are negatively correlated with NINO3 SSTs as in the observations. Spectra of time series of Indian monsoon. Australian monsoon, and NINO3 SST indices from the CSM show amplitude peaks in the Southern Oscillation and tropospheric biennial oscillation frequencies (3-6 yr and about 2.3 yr, respectively) as observed. Lag correlations between the NINO3 SST index and upper-ocean heat content along the equator show eastward propagation of heat content anomalies with a phase speed of about 0.3 m s super(-) super(1) , compared to observed values of roughly 0.2 m s super(-) super(1) . Composites of El Nino (La Nina) events in the CSM show similar seasonal evolution to composites of observed events with warming (cooling) of greater than several tenths of a degree beginning early in northern spring of year 0 and diminishing around northern spring of year +1, but with a secondary resurgence in the CSM events later in northern spring of year +1. The CSM also shows the largest amplitude ENSO SST and low-level wind anomalies in the western tropical Pacific, with enhanced interannual variability of SSTs extending northeastward and southeastward toward the subtropics, compared to largest interannual SST variability in the central and eastern tropical Pacific in the observations.

Meehl, G. A. and J. M. Arblaster (2002). "Indian Monsoon GCM Sensitivity Experiments Testing Tropospheric Biennial Oscillation Transition Conditions." Journal of Climate 15(9): 923-944.

Observational studies have shown that the tropospheric biennial oscillation (TBO) involves transitions that occur from northern spring [March-April-May (MAM)] to the Indian monsoon season [June-July-August-September (JJAS)] such that a relatively strong monsoon the previous year is often followed by a relatively weak one, and vice versa. Several conditions involving anomalous land and ocean surface temperature anomalies in the Indo-Pacific region in MAM have been identified to be associated with TBO monsoon transitions. Though it is possible to quantify the relative contribution of each transition condition year by year in observations, they are interrelated and the question remains whether each condition by itself could cause a monsoon transition. Here, a series of GCM sensitivity experiments is performed to isolate the effects of each of the transition conditions to document their respective influences on the anomalous patterns of monsoon rainfall associated with TBO transitions. Three conditions postulated to contribute to these TBO transitions associated with Indian monsoon rainfall are 1) atmospheric circulation-related anomalous south Asian land temperatures and resulting meridional temperature gradients, 2) anomalous SSTs in the Indian Ocean, and 3) anomalous tropical Pacific SSTs. Sensitivity experiments with an atmospheric GCM (the NCAR CCM3) are performed to address these conditions by specifying 1) warmer land temperatures over Asia to produce a stronger meridional temperature gradient, 2) warm Indian Ocean SST anomalies, and 3) cold Pacific Ocean SST anomalies. The model results demonstrate that each of the transition conditions is associated with distinct physical processes and can contribute to a relative TBO transition in monsoon strength by themselves. The anomalous tropical Indian and Pacific Ocean SST anomalies produce a larger monsoon response in the model compared to the anomalous meridional temperature gradient over Asia indicating they are the dominant conditions associated with TBO transitions. The location of the SST anomalies over the tropical Indian Ocean is important, with warm SST anomalies throughout the tropical Indian Ocean producing enhanced rainfall over the ocean and south Asian land areas, and warm SST anomalies near the equatorial Indian Ocean producing increased rainfall locally with decreased rainfall over south Asian lan