References for “The Asian Monsoon” book – Chapter 7

Annamalai, H. (1995). "Intrinsic problems in the seasonal prediction of the Indian summer monsoon rainfall." Meteorology and Atmospheric Physics, Vienna, Austria 55(1-2): 61-76.

The latest non-parametric statistical tool Singular Spectrum Analysis (SSA) has been shown to extract deterministic oscillations present in a nonlinear dynamical system. It has been hypothesized that the tropical ocean-atmosphere system consists of both deterministic and stochastic parts in the inter-annual time scales. In the present study SSA has been employed to extract the deterministic and random parts present in the Indian summer monsoon (ISM) and its predictors time series data sets. The dominant eigenmode pair of the ISM does not emerge as a pure and deterministic oscillation. However, about 34% variance is deterministically predictable in the inter-annual range. The second pair is significantly related to the first pair of Darwin pressure tendency and both emerge as deterministic parts. This relationship partially answers the questions raised by Webster and Yang (1992). The low frequency component of ENSO emerges as a deterministic oscillation in all the variables except in Bombay pressure tendency. The presence of decadal-scale oscillations may possibly be responsible for the instability in the relationship between the ISM and its predictors. Some plausible explanations for the percent variance explained by the predictors in the existing empirical models have also been discussed. It has been proposed that empirical models can be constructed only with the deterministic parts which may help improve the predictive skill of existing models.

Black, D. E. (2002). "The Rains May Be A-Comin'." Science (Washington) 297(5581): 528-529.

Reconstructions of long-term climate change often focus on individual climate factors such as surface temperature. More comprehensive long-term climate records exist for some climate systems, such as the El Nino-Southern Oscillation and the North Atlantic Oscillation, but not for others, including the Southwest Asian monsoon. Anderson et al. now provide much-needed insights into the decadal- and centennial-scale variability of the Asian monsoon. On page 596 of this issue, they present a 1000-year sediment record of variations in the southwest monsoon winds from the Oman Margin in the Arabian Sea.

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.

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.

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).

Chowdhury, A. and V. P. Abhyankar (1984). "On some climatological aspects of drought in India." Mausam, New Delhi 35(3): 375-378.

On the basis of data from 1875 to 1980, an attempt is made to compile a drought climatology of India. Only meteorological drought, i.e., rainfall deficiency >25% of the normal is considered. The frequency of drought occurrence in different meteorological subdivisions has been obtained and used to determine its recurrence period. Drought is classified into moderate and severe categories, and the probability of occurrence of these types in different subdivisions is computed and discussed. Depending upon the area of the country affected, drought is further classified as localized, semivast, vast, extensive, and calamitous, and the observed frequency of each type is given. Decadal representation of drought incidence is used to predict its occurrence in any 10-yr period. The series is also subjected to power spectrum analysis, and significant peaks are obtained and discussed. Since there is now no rational criteria to define a year as a good or bad monsoon year for the country as a whole, an objective and pragmatic approach to solve this problem is attempted. The following two categories are separately adopted to consider a year as a drought year: 1) when the percentage area affected >20%, and 2) when the area >25%. Sequences of a drought year or a good monsoon year have been obtained and have been examined to obtain probabilities of a drought year following 3 consecutive good years, 4 good years, and 5 good years. Similarly, chances of two consecutive years of drought after each of 3, 4, and 5 consecutive good monsoon years have been determined. These sequences have also been used to find persistence in occurrence of good or bad (drought) monsoon years and have been subjected to the chi super(2) -test to determine their statistical significance.

Chu, P.-S. and J.-B. Wang (1997). "Recent climate change in the tropical western Pacific and Indian Ocean regions as detected by outgoing longwave radiation records." Journal of Climate, Boston, MA 10(4): 636-646.

Recent climate change in tropical convection in the western Pacific and Indian Ocean regions is inferred from the outgoing longwave radiation (OLR) records. The systematic bias in the OLR series is first corrected and results of the rotated empirical orthogonal function analysis indicate that the bias, to a first approximation, has been corrected. Linear regression analysis and nonparametric Mann-Kendall rank statistics are employed to detect trends. From 1974 to 1992, trend analyses based on the entire consecutive monthly records suggest a significant decrease in OLR over the tropical central-western Pacific and a large portion of the Indian Ocean. In contrast, northern Australia shows the largest increase in OLR over time. The significance of the local linear trend pattern has been determined via a Monte Carlo simulation technique that scrambles OLR time series at each grid point ``simultaneously'' and results show the field significance. An increase in convection shows a preference to occur in the summer hemisphere. During the boreal summer half-year, this is seen in a region extending from the Arabian Sea across southeast Asia eastward to the northwest Pacific, with the largest value over the Bay of Bengal. More summer monsoon rainfall is likely to have occurred in these regions. For the austral summer half-year, enhanced convection is found over the equatorial south-central Pacific and the south-central Indian Ocean. Time series of tropical cyclone counts in the northwest Pacific, the Bay of Bengal, and the south-central Indian Ocean also reveal a general level of increase. Regardless of seasonality, a positive trend in OLR is always observed over a large portion of tropical Australia. A sensitivity test is conducted to investigate the change in linear trend patterns by removing the years during which the El Nino-Southern Oscillation phenomenon occurred. Although the enhanced convection over the Bay of Bengal, the south Indian Ocean, and the northwest Pacific are still noticeable, it is much weaker over the equatorial south-central Pacific than when the complete duration series were used. Other sensitivity tests are also conducted to examine the change in linear trend patterns by varying data lengths and by skipping the missing 10-month observation in the OLR time series; results are basically similar to those when complete data are used. The authors speculate that monsoon convection over the tropical western Pacific and the Indian Ocean has undergone a change in the climate mean state, probably on a decadal timescale.

Clark, C. O., J. E. Cole, et al. (2000). "Indian Ocean SST and Indian summer rainfall: predictive relationships and their decadal variability." Corrigendum Journal of Climate, Boston, MA 13(24).

In Clark et al. (2000), the regression equation is in error. The correlation coefficient between the Nino-3 SST index and the SST at each gridpoint, r, was omitted. The correct equation is presented here.

Clark, C. O., J. E. Cole, et al. (2000). "Indian Ocean SST and Indian summer rainfall: predictive relationships and their decadal variability." Journal of Climate, Boston, MA 13(14): 2503-2519.

The authors examine relationships between Indian Ocean sea surface temperature (SST) variability and the variability of the Indian monsoon, including analysis of potential long-lead predictions of Indian rainfall by regional SST and the influence of ENSO and decadal variability on the stability of the relationships. Using monthly gridded (4 degrees x 4 degrees ) SST data from the Global Sea-Ice and Sea Surface Temperature (GISST) dataset that spans 1945-94, the correlation fields between the All-India Rainfall Index (AIRI) and SST fields over the tropical Indian Ocean are calculated. In the boreal fall and winter preceding the summer Indian monsoon, SST throughout the tropical Indian Ocean correlates positively with subsequent monsoon rainfall. Negative correlation occurs between SST and the AIRI in the subsequent autumn in the northern Indian Ocean only. A strong correlation (0.53) is found between the summer AIRI and the preceding December-February Arabian Sea SST. The correlation between the AIRI and the SST to the northwest of Australia for the same period is 0.58. The highest correlation (0.87) for the years following 1977 is found between the AIRI and the central Indian Ocean SST in the preceding September-November, but this relationship is much weaker in earlier years. Based upon these correlations, the authors define Arabian Sea (AS1), northwest Australia (NWA1), and central Indian Ocean (CIO1) SST indexes. The relationships of these indexes to the AIRI and ENSO are examined. The authors find that the high correlation of the AS1 and NWA1 SST indexes with the Indian summer rainfall is largely unaffected by the removal of the ENSO signal, whereas the correlation of the CIO1 index with the AIRI is reduced. The authors examine the interdecadal variability of the relationships between SST and the AIRI and show that the Indian Ocean has undergone significant secular variation associated with a climate shift in 1976. The possible mechanisms underlying the correlation patterns and the implications of the relationship to the biennial nature of the monsoon and predictability are discussed.

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.

Dugam, S. S. and S. B. Kakade (1995). "Short-term climatic fluctuations in North Atlantic oscillation and frequency of cyclonic disturbances over North Indian Ocean and Northwest Pacific." Advances in Atmospheric Sciences, Beijing, China 12(3): 371-376.

A relationship between mean sea level pressure gradient between Azores High (AH) and Icelandic Low (IL) here after called North Atlantic Oscillation Index (NAOI) and the frequency of cyclonic disturbances over North Indian Ocean is investigated using 98 years of date (1891-1988). The analysis is carried out on monthly, seasonal, annual and decadal scales. Similar studies are also done for Northwest Pacific ocean cyclonic disturbances. It is noticed that the number of cyclonic disturbances over North Indian Ocean during monsoon season (June-September) as well as on annual scale is significantly correlated with NAOI. However for pre (April-May) and post (October-November-December) monsoon seasons frequency of cyclonic disturbances do not bear similar relationship with NAOI. The study also shows that decadal scale variability of cyclonic disturbances during the summer monsoon over North Indian Ocean has a remarkable correspondence with the decadal variability of NAOI.

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.

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.

Gao, D. and B. Wu (1998). "A preliminary study on decadal oscillation and its oscillation source in the sea-ice-air system in the Northern Hemisphere." Polar Meteorology and Glaciology, Tokyo, Japan 12: 68-78.

By using maximum entropy and band-pass filter methods, the variation periods of sea ice area index in the Kara/Barents Seas, the intensity index of the Siberian High and winter monsoon over East Asia during winters from 1953 to 1990 were analyzed. And sea ice area variation in winter in the Kara/Barents Seas was compared with the area and intensity indices of the subtropical high in the following spring and summer. The results indicate that there is an obvious decadal variation in the sea-ice-air system in the Northern Hemisphere. The variations of intensity index of the winter Siberian High and the winter monsoon over East Asia are out of phase with that of sea ice area in winter in the Kara/Barents Seas. The more (less) sea ice there is, the weaker (stronger) the winter Siberian High and winter monsoon are. The variation trend of sea ice area is similar to that of the area and the intensity of the subtropical high in the coming spring and summer, with a lag period of 0-1 year. The decadal oscillation sources in the atmosphere are closely linked to specific sea regions. The center of the strongest oscillation source excited by winter sea ice in the Kara/Barents Seas is near 70 degrees E, 60 degrees N.

Ge, Z., Q. Wang, et al. (1996). "Features of decadal mean and anomaly of monsoon circulations in years of severe flood/drought." Journal of Nanjing Institute of Meteorology, Nanjing, China 19(3): 358-363.

In the context of ECMWF height data, investigation is conducted of the decadal mean and anomaly characteristics of major summer monsoon systems in May, 1985 (of drought) and 1991 (severe flood). Evidence suggests that the position and vigor of the monsoons greatly differ from decade to decade between the years; summer rainfall anomaly is associated not merely with the anomalous activities of South-Asian high, polar vortex and western Pacific subtropical high but with the strength of Australian cold high and Mascarene high, and even with the meridionality of circulations at southern extropics as well.

Geevan, C. P. (1996). "Report on `Global analysis, interpretation and modelling (GAIM) science conference'." Current Science, Bangalore, India 70(1): 10-11.

The recently concluded GAIM Science Conference, organized by the International Geosphere-Biosphere Program, September 25-29, 1995, Garmisch-Partenkirchen, Germany brought together over 300 scientists from 44 countries in a major effort to advance the study of the coupled dynamics of Earth system using both empirical studies and computer models. The focus was on biogeochemical cycles, as well as the identification and assessment of natural and anthropogenic changes in the various subsystems of the Earth. Studies of paleo-climate, as inferred from indirect measurements, show that climate change is largely the reaction to forcings such as orbital, solar and volcanic dust with superimposed noise. Methane, a radiatively active trace gas, is of great significance in understanding past climate conditions. Much attention was paid to the signatures left by past climate changes in the form of distinct isotope ratios, reflecting the interplay of physical, chemical and biological processes. Reports of computer simulations using orbital conditions for the period 6 ky BP showed enhanced seasonal cycle in the Northern Hemisphere, with a stronger African-Asian summer monsoon. It was reported that a study of the lake records for 6 ky BP, point to a major expansion of the Afro-Asian monsoon. These studies also show that the climate of 6 ky BP was significantly different from today with respect to the regional water balance. Results from all the three major classes of global terrestrial biosphere models--(1) atmospheric general circulation models, (2) equilibrium vegetation models and (3) terrestrial biogeochemical models, were discussed. Some of the presentations departed from the tradition of considering vegetation as an invariant aspect of general circulation models of climate and signified a reflection of the growing realization that vegetation is, indeed, an integral part of the climate system and that changes in vegetation structure and function can influence climate. It was argued that the presence of seasonal, biennial and decadal signals in atmospheric CO sub(2) linked to variations in climate parameters, offers a valuable testing ground for terrestrial carbon cycle models. A special session on developing countries underscored the importance of tropical and sub-tropical regions in the study of global environmental change and noted that the success of global change research will depend on both expertise and data from all parts of the globe.

Gershunov, A., N. Schneider, et al. (2001). "Low-Frequency Modulation of the ENSO-Indian Monsoon Rainfall Relationship: Signal or Noise?" Journal of Climate 14(11): 2486-2492.

Running correlations between pairs of stochastic time series are typically characterized by low-frequency evolution. This simple result of sampling variability holds for climate time series but is not often recognized for being merely noise. As an example, this paper discusses the historical connection between El Nino-Southern Oscillation (ENSO) and average Indian rainfall (AIR). Decades of strong correlation ( similar to -0.8) alternate with decades of insignificant correlation, and it is shown that this decadal modulation could be due solely to stochastic processes. In fact, the specific relationship between ENSO and AIR is significantly less variable on decadal timescales than should be expected from sampling variability alone.

Gershunov, A., N. Schneider, et al. (2001). "Low-frequency modulation of the ENSO-Indian monsoon rainfall relationship: signal or noise?" Journal of Climate, Boston, MA 14(11): 2486-2492.

Running correlations between pairs of stochastic time series are typically characterized by low-frequency evolution. This simple result of sampling variability holds for climate time series but is not often recognized for being merely noise. As an example, this paper discusses the historical connection between El Nino-Southern Oscillation (ENSO) and average Indian rainfall (AIR). Decades of strong correlation ( similar to -0.8) alternate with decades of insignificant correlation, and it is shown that this decadal modulation could be due solely to stochastic processes. In fact, the specific relationship between ENSO and AIR is significantly less variable on decadal timescales than should be expected from sampling variability alone.

Hastenrath, S. and L. Greischar (1993). "Changing predictability of Indian monsoon rainfall anomalies?" Proceedings, Bangalore, India 102(1): 35-47.

The predictability of Indian summer monsoon rainfall from pre-season circulation indices is explored from observations during 1939-91. The predictand is the all-India average of June-September precipitation NIR, and the precursors examined are the latitude position of the 500 mb ridge along 75 degrees E in April (L), the pressure tendency April minus January at Darwin (DPT), March-April-May temperature at six stations in west central India (T6), the sea surface temperature (SST) anomaly in the northeastern Arabian Sea in May (ASM), SST anomaly in the Arabian Sea in January (ANJ), Northern Hemisphere temperature anomaly in January-February (NHT), and Eurasian snow cover in January (SNOW). Monsoon rainfall tends to be enhanced with a more northerly ridge position, small Darwin pressure tendency, warmer pre-season conditions, and reduced winter snow cover. However, relationships have varied considerably over the past half-century, with the strongest associations during 1950-80, and a drastic weakening in the 1980s. Four prediction models were constructed based on stepwise multiple regression, using as predictors combinations of L, DPT, T6, ASM, and NHT, with 1939-68 as ``dependent'' dataset, or training period, and 1969-91 as ``independent'' dataset or verification period. For the 1969-80 portion of the verification period calculated and observed NIR values agreed closely, with the models explaining 74-79% of the variance. By contrast, after 1980 predictions deteriorated drastically, with the explained variance for the 1969-89 time span dropping to 25-31%. The monsoon rainfall of 1990 and 1991 turned out to be again highly predictable from models based on stepwise multiple regression and linear discriminant analysis and using as input L+DPT or L+DPT+NHT, and with this encouragement an experimental real-time forecast was issued of the 1992 monsoon rainfall. These results underline the need for investigations into decadal-scale changes in the general circulation setting and raise concern for the continued success of seasonal forecasting.

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.

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. 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.

Hu, Z.-Z., L. Bengtsson, et al. (2000). "Impact of global warming on the Asian winter monsoon in a coupled GCM." Journal of Geophysical Research, Washington, DC 105(D4): 4607-4624.

The Asian winter monsoon (AWM) response to the global warming was investigated through a long-term integration of the transient greenhouse warming with the ECHAM4/OPYC3 CGCM. The physics of the response was studied through analyses of the impact of the global warming on the variations of the ocean and land contrast near the ground in the Asian and western Pacific region and the east Asian trough and jet stream in the middle and upper troposphere. Forcing of transient eddy activity on the zonal circulation over the Asian and western Pacific region was also analyzed. It is found that in the global warming scenario the winter northeasterlies along the Pacific coast of the Eurasian continent weaken systematically and significantly, and intensity of the AWM reduces evidently, but the AWM variances on the interannual and interdecadal scales are not affected much by the global warming. It is suggested that the global warming makes the climate over the most part of Asia to be milder with enhanced moisture in winter. In the global warming scenario the contrasts of the sea level pressure and the near-surface temperature between the Asian continent and the Pacific Ocean become significantly smaller, northward and eastward shifts and weakening of the east Asian trough and jet stream in the middle and upper troposphere are found. As a consequence, the cold air in the AWM originating from the east Asian trough and high latitudes is less powerful. In addition, feedback of the transient activity also makes a considerable contribution to the higher-latitude shift of the jet stream over the North Pacific in the global warming scenario.

Huang, R., L. Zhou, et al. (2003). "The Progresses of Recent Studies on the Variabilities of the East Asian Monsoon and Their Causes." Advances in Atmospheric Sciences 20(1): 55-69.

The variabilities of the East Asian summer monsoon are an important research issue in China, Japan, and Korea. In this paper, progresses of recent studies on the intraseasonal, interannual, and interdecadal variations of the East Asian monsoon, especially the East Asian summer monsoon, and their causes are reviewed. Particularly, studies on the effects of the ENSO cycle, the western Pacific warm pool, the Tibetan Plateau and land surface processes on the variations of the East Asian summer monsoon are systematically reviewed.

Hunt, B. G. and H. L. Davies (1997). "Mechanism of multi-decadal climatic variability in a global climatic model." International Journal of Climatology, Chichester, UK 17(6): 565-580.

A 500-year run has been made with a global climatic model for current climatic conditions using a simple slab ocean with inferred oceanic heat transfers. The model exhibited multi-decadal warming and cooling episodes with changes in globally averaged, annual mean surface temperature of up to 0.7 degrees C. The length of the individual episodes varied, but 50-60 years was typical for major episodes. Examination of the geographical distribution of climatic variables for warm or cool episodes revealed distinct differences, particularly of surface temperature and low-level zonal wind, with considerable activity concentrated over the low-latitude Pacific Ocean. Each multi-decadal warming and cooling episode experienced pulsations of about 3-5 years duration associated with westerly wind bursts over the western Pacific Ocean. These bursts were related to the behaviour of the Asian monsoon, and, in turn, a connection between activity over the Pacific Ocean and the Asian monsoon was identified via the global distribution of velocity potential. The wind bursts produced warmings of the low-latitude, central Pacific Ocean and showed a number of features characteristic of the atmospheric phase of an ENSO event. The centre of activity producing the multi-decadal variability was determined to be the low-latitude Pacific Ocean, and analysis was subsequently concentrated on this region. The major factor controlling the multi-decadal warming and cooling episodes was cloud variability. During a cooling episode low-level cloud amount increased whereas high-level cloud amount decreased, with both variations contributing to the overall cooling. The reverse situation applied during a warming episode. A necessary precursor to a cooling episode was a build up in low-level moisture in the atmosphere sufficient to sustain the subsequent low-level cloud amount as the cooling progressed. The termination of a cooling episode resulted from a reduction in the total cloud amount, attributed to the high- and medium-level cloud, despite the increase in low-level cloud amount. This reduction permitted sufficient solar radiation to reach the surface in low latitudes to initiate a warming and trigger deep convection and thus recharge the high-level cloud amount, which then enhanced the initial solar-induced surface warming.

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).

Isdale, P. J., B. J. Stewart, et al. (1998). "Palaeohydrological variation in a tropical river catchment: a reconstruction using fluorescent bands in corals of the Great Barrier Reef, Australia." The Holocene, London, UK 8(1): 1-8.

Massive, long-lived corals in inshore waters of the Great Barrier Reef contain yellow-green fluorescent bands. These bands are due to terrestrial humic and fulvic compounds incorporated into the coral skeleton during high river flow events. Fluorescence measurements are presented for two colonies of Porites spp. from locations in the path of the Burdekin River floodwaters--the major river in north Queensland draining into the Coral Sea. The records extend from AD 1737 to 1980 and 1644 to 1986, respectively. The two independent coral records show a high degree of similarity. The two series are combined and used to reconstruct Burdekin River runoff for the period AD 1644 to 1980. The regression model accounts for 83% of the annual (water year) variability of Burdekin River flow and is verified over independent data. The 337-year reconstruction thus increases by threefold the length of record for considering interannual to decadal climate variations in northeast Australia. Instrumental and reconstructed Burdekin River runoff are closely related to an index of summer monsoon rainfall in Queensland. Thus, the reconstruction provides insights into the behaviour over the past three centuries of both a major tropical river system and the highly variable summer monsoon rainfall in northeast Australia. The reconstructed series shows wetter conditions (higher runoff) in the late-seventeenth to mid-eighteenth centuries and in the late-nineteenth century. Drier conditions (lower runoff) are reconstructed in the late-eighteenth to mid-nineteenth centuries and in the mid-twentieth century.

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.

Jinhong, Z. and W. Shaowu (2001). "80a-Oscillation of Summer Rainfall over the East Part of China and East-Asian Summer Monsoon." Advances in Atmospheric Sciences 18(5): 1043-1050.

Relationship between summer rainfall over the east part of China and East-Asian Summer Monsoon (EASM) was studied based on the summer rainfall grade data set from 1470 to 1999 and the rain gauge data set from 1951 to 1999 over the east part of China, and sea level pressure (SLP) data for the period of 1871-2000. A distinct 80a-oscillation of summer rainfall was found over North China (NC), southern part of Northeast China, over the middle and lower reaches of the Yangtze River (YR) and South China (SC). The 80a oscillation of summer rainfall over NC was varied in phase with that over SC, and was out of phase to that along the middle and lower reaches of the Yangtze River. Summer rainfall over NC correlated negatively with the SLP averaged for the area from 105 degree E to 120 degree E, and from 30 degree N to 35 degree N, but positively to that for the area from 120 degree E to 130 degree E, and from 20 degree N to 25 degree N. Therefore, an index of EASM was defined by the difference of averaged SLP over the two regions. The summer rainfall over NC was greater than normal when the EASM was strong, and while drought occurred along the middle and lower reaches of the Yangtze River. The drought was found over NC, and flood along the middle and lower reaches of the Yangtze River when the EASM was close to normal. Finally, the interdecadal variability of EASM was studied by using of long term summer rainfall grade data set over NC for the past 530 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.

Kinter, J. I. and K. Miyakoda (2002). "Recent Change in the Connection from the Asian Monsoon to ENSO." Journal of Climate 15(10): 1203-1215.

The Asian monsoon and El Nino-Southern Oscillation (ENSO) are known to interact with each other. In this paper, four primary indices (the Indian monsoon rainfall index, the Webster and Yang monsoon index, the tropical-wide oscillation index, and the Southern Oscillation index) that characterize the temporal variation of these complex, chaotic and quasi-oscillatory phenomena are used to assess the action from the Asian monsoon to ENSO, that is, the linkage between the strong/weak monsoon and La Nina/El Nino. The evolution of the four previously documented indices and other auxiliary data over a 43-yr period is examined using the observed database and the reanalysis of the National Centers for Environmental Prediction. The Asian monsoon and ENSO intersect in a common area, namely, the warm pool in the western tropical Pacific. This region (e.g., 10 'S-5 'N, 110 '-170 'E) is located at the longitudinally central portion of the Walker circulation and also the equatorial end of the Indo-Pacific meridional overturning cell that is part of the zonal mean Hadley circulation. In recent decades, the connection between the monsoon and ENSO has changed considerably. This change is related to the atmospheric circulation over the entire North Pacific Ocean, which entered a new regime in about 1976. Before 1976, the correlations among the four primary indices, and those between the indices and the Nino-3 index of sea surface temperature, were strong. In recent decades, the ocean temperature in the entire North Pacific became considerably colder. The lower-tropospheric winds became simultaneously more cyclonic over the North Pacific. ENSO is now related to atmospheric fluctuations both in the Indian sector and in northeastern China. The western North Pacific monsoon in the vicinity of the Philippine Islands (9 '-19 'N, 139 '-141 'E) may play an important role together with the off-equatorial ocean heat content in a larger region (5 '-15 'N, 135 '-170 'E) in maintaining or even increasing ENSO activities.

Klein, R., A. W. Tudhope, et al. (1997). "Evaluating southern Red Sea corals as a proxy record for the Asian monsoon." Earth and Planetary Science Letters, New York, NY 148(1-2): 381-394.

Coral palaeoclimatic studies are under way at many sites throughout the wet tropics. However, arid environments have received less attention. Here we report a high-resolution, 63 yr record of coral delta super(1) super(8) O and delta super(1) super(3) C extracted from a Porites colony from the Dahlak Archipelago, off the Eritrean coast, in the southern Red Sea. The annual cycles of the coral delta super(1) super(8) O and delta super(1) super(3) C are inversely related while their inter-annual variations show a strong positive correlation, with similar inter-decadal trends. Inter-annual variations in coral delta super(1) super(8) O show a relatively weak correlation with the southern Red Sea SST, but are strongly correlated with the Indian Ocean SST, especially on the decadal time-scale. The range of the inter-annual variations in the coral delta super(1) super(8) O is high compared to changes in local SST, due to the amplifying effect of simultaneous changes in water isotopic composition. Due to this amplification of the climate signal the coral provides a better indication of regional oceanographic behaviour than the local SST record. The northeast monsoon signal in the coral delta super(1) super(8) O dominates the mean annual signal and shows the best correlation with the instrumental data sets. It appears that variations in the coral delta super(1) super(8) O are controlled mainly by variations in the intensity of surface water influx from the Indian Ocean to the Red Sea during the winter northeast monsoon. Of particular significance is that the decadal time-scale variations in the coral skeletal delta super(1) super(8) O are closely correlated with both the Indian Ocean SST and with variations in the Pacific-based Southern Oscillation index. That is, isotopically light coral skeleton, indicating strong NE monsoon Red Sea inflow, correlates with periods of high Indian Ocean SST and with predominantly negative (El Nino) phases of the Southern Oscillation. The simultaneous nature of inter-decadal changes in Asian monsoon and ENSO behaviour suggest pan-Indo-Pacific tropical climate reorganisation and evolution.

Kripalani, R. H. and A. Kulkarni (1997). "Rainfall variability over south-east AsiaAconnections with Indian monsoon and ENSO extremes: new perspectives." International Journal of Climatology, Chichester, UK 17(11): 1155-1168.

Seasonal and annual rainfall data for 135 stations for periods varying from 25 to 125 years are utilized to investigate and understand the interannual and short-term (decadal) climate variability over the South-east Asian domain. Contemporaneous relations during the summer monsoon period (June to September) reveal that the rainfall variations over central India, north China, northern parts of Thailand, central parts of Brunei and Borneo and the Indonesian region east of 120 degrees E vary in phase. However, the rainfall variations over the regions surrounding the South China Sea, in particular the north-west Philippines, vary in the opposite phase. Possible dynamic causes for the spatial correlation structure obtained are discussed. Based on the instrumental data available and on an objective criteria, regional rainfall anomaly time series for contiguous regions over Thailand, Malaysia, Singapore, Brunei, Indonesia and Philippines are prepared. Results reveal that although there are year-to-year random fluctuations, there are certain epochs of the above- and below-normal rainfall over each region. These epochs are not forced by the El Nino/La Nina frequencies. Near the equatorial regions the epochs tend to last for about a decade, whereas over the tropical regions, away from the Equator, epochs last for about three decades. There is no systematic climate change or trend in any of the series. Further, the impact of El Nino (La Nina) on the rainfall regimes is more severe during the below (above) normal epochs than during the above (below) normal epochs. Extreme drought/flood situations tend to occur when the epochal behaviour and the El Nino/La Nina events are phase-locked.

Kripalani, R. H. and A. Kulkarni (1999). "Climatology and variability of historical Soviet snow depth data: some new perspectives in snow-Indian monsoon teleconnections." Climate Dynamics, Berlin, Germany 15(6): 475-489.

This study presents the monthly climatology and variability of the historical soviet snow depth data. This data set was developed under the bilateral data exchange agreement between United States of America and the former Union of Soviet Socialist Republics. The original data is for 284 stations for periods varying from 1881 upto 1985. The seasonal cycle of the mean snow depth has been presented both as spatial maps and as averages over key locations. The deepest snow (=80 cms/day) areas are found over Siberia (in Particular over 80'-100'E, 55'-70'N) during March. Over the course of the annual cycle average snow depth over this region changes dramatically from about 10 cms in October to about 80 cms in March. The variability is presented in the form of spatial maps of standard deviation. To investigate the interaction of snow depth with Indian monsoon rainfall (IMR), lag and lead correlation coefficients are computed. Results reveal that the winter-time snow depth over western Eurasia surrounding Moscow (eastern Eurasia in central Siberia) shows significant negative (positive) relationship with subsequent IMR. Following the monsoon the signs of relationship reverse over both the regions. This correlation structure is indicative of a midlatitude longwave pattern with an anomalous ridge (trough) over Asia during the winter prior to a strong (weak) monsoon. As the time progresses from winter to spring, the coherent areas of significant relationship show southeastward propagation. Empirical orthogonal function analysis of the snow depth reveal that the first mode describes a dipole-type structure with one centre around Moscow and the other over central Siberia, depicting similar pattern as the spatial correlation structure. The decadal-scale IMR variations seem to be more associated with the Northern Hemisphere midlatitude snow depth variations rather than with the tropical ENSO (El Nino Southern Oscillation) variability.

Kripalani, R. H. and A. Kulkarni (2001). "Monsoon rainfall variations and teleconnections over South and East Asia." International Journal of Climatology, Chichester, UK 21(5): 603-616.

Seasonal summer monsoon (June-September) data for 120 stations over East Asia (China, Japan, Mongolia, Korea) varying from 1881 to 1998 are utilized to understand their interannual and climate characteristics, and to investigate their teleconnections with South Asian (in particular India's) monsoon rainfall. Contemporaneous relations on an interannual time-scale reveal that the rainfall variations over north China (southern Japan) are in-phase (out-of-phase) with South Asian rainfall. Based on the instrumental data available, regional rainfall anomaly time series for the 118-year period for the two coherent regions, over north China and southern Japan are prepared. All the three series (India, China, Japan) have been subjected to statistical tests. Results reveal that while there are year-to-year fluctuations, the Mann-Kendall rank statistic suggests no significant long-term trends. However, the application of Cramer's statistic to study the short-term climate variability depicts decadal variability with certain epochs of above and below normal rainfall over each region. The epochs tend to last for about three decades over India and China, and about five decades over Japan. The turning points for China follow those of India about a decade later. The relationships of South and East Asian monsoon rainfall exhibit secular variations. The inter-connections between the monsoon-related events (rainfall over South Asia, rainfall over East Asia, Northern Hemisphere circulation, tropical Pacific circulation) appear to strengthen (or weaken) around the same time, implying that the monsoon related events over geographically separated regions seem to get linked (or delinked) around the same time.

Kripalani, R. H., A. Kulkarni, et al. (1997). "Association of the Indian summer monsoon with the Northern Hemisphere mid-latitude circulation." International Journal of Climatology, Chichester, UK 17(10): 1055-1067.

The association between the mid-latitude circulation and rainfall over the Indian region on an intraseasonal time-scale is investigated by considering 11 years (1974-1984) of Northern Hemisphere 500 hPa geopotential heights and rainfall data for the Indian summer monsoon months June through to September. On the basis of extensive correlation analysis between the geopotential heights and rainfall, it is seen that three regions over the mid-latitudes, the Manchurian region, the Algerian region and the Caspian sea region show positive correlation with rainfall over India, with higher values north of 20 degrees N latitude. Lead and lag correlations between the heights at the locations identified above and rainfall over India reveals that some common element of low-frequency variability is influencing the mid-latitude circulation and Indian rainfall. On the interannual scale the connections between the winter-time low-frequency patterns (the Pacific/North Atlantic, the West Pacific Oscillation, the North Atlantic Oscillation and the Eurasian) and Indian summer monsoon rainfall (ISMR) are investigated. Only the West Pacific Oscillation pattern shows a significant relationship with the ISMR. Further, the interannual and the decadal variability is examined by using the Northern Hemisphere zonal index data for the period 1900-1993. Results reveal that the decadal-scale variability of the ISMR and the circulation features of the Northern Hemisphere are connected.

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.

Kumar, J. and S. K. Dash (2001). "Interdecadal variations of characteristics of monsoon disturbances and their epochal relationships with rainfall and other tropical features." International Journal of Climatology, Chichester, UK 21(6): 759-771.

Interdecadal variations of some characteristics (number and duration) of different monsoon disturbances (low pressure areas (lows), depressions and cyclonic storms (CS)) over the Indian region are studied for 110 years (1889-1998) to find whether an epochal variation exists in such main synoptic components of the Indian summer monsoon at the decadal time scale, similar to other long-term interdecadal variations of tropical features, e.g. Indian summer monsoon rainfall (ISMR), El Nino-Southern Oscillation Index (SOI), sub-tropical ridge (STR) over India, Northern Hemispheric surface temperature (NHST), etc. As ISMR has alternate epochs of below and above normal phases at the broad time scale of 30 years, variations of these features are also examined according to the two epochs of ISMR. The stability of correlation of monsoon disturbance days with ISMR is also examined for the same 30-year time scale for 1889-1998. Stability of relationships of other tropical features and monsoon disturbance days with ISMR is also examined, based on their 11-year moving correlation coefficients (CC). Results do not show any regular trend in decadal frequencies of the number or duration of different monsoon disturbances. However, decadal frequencies of number of depressions, CS and depressions are decreasing from 1969-1978 until the most recent decade. During the recent decade, less than half of the total number of depressions and CS are formed, compared with 1969-1978. On the other hand, the total number of lows increases significantly from 1959-1968 to the recent decade, when more than double the number of lows are formed. By examining the 30-year periodicity of the number of disturbances together or separately, it is found that depressions and CS are higher during the above normal epochs, and significantly less during the below normal epochs of ISMR. The reverse is true for the number of lows and the total number of disturbances and their total duration. The 11-year running means of monsoon disturbance days with ISMR shows the same behaviour but opposite epochs during 1929-1958 and 1970-1990. Their correlation coefficients are also found to be lower during 1929-1958 compared with epochs when they are in the same phase. Comparison of epochal relationships with other tropical features, e.g. El Nino, SOI, STR, NHST etc., from 11-year running means and their 11-year moving CC with ISMR, have also shown epochal fluctuations.

Latif, M., D. Anderson, et al. (1998). "A review of the predictability and prediction of ENSO." Journal of Geophysical Research, Washington, DC 103(C7): 14375-14393.

A hierarchy of El Nino-Southern Oscillation (ENSO) prediction schemes has been developed during the Tropical Ocean-Global Atmosphere (TOGA) program which includes statistical schemes and physical models. The statistical models are, in general, based on linear statistical techniques and can be classified into models which use atmospheric (sea level pressure or surface wind) or oceanic (sea surface temperature or a measure of upper ocean heat content) quantities or a combination of oceanic and atmospheric quantities as predictors. The physical models consist of coupled ocean-atmosphere models of varying degrees of complexity, ranging from simplified coupled models of the ``shallow water'' type to coupled general circulation models. All models, statistical and physical, perform considerably better than the persistence forecast in predicting typical indices of ENSO on lead times of 6 to 12 months. The TOGA program can be regarded as a success from this perspective. However, despite the demonstrated predictability, little is known about ENSO predictability limits and the predictability of phenomena outside the tropical Pacific. Furthermore, the predictability of anomalous features known to be associated with ENSO (e.g., Indian monsoon and Sahel rainfall, southern African drought, and off-equatorial sea surface temperature) needs to be addressed in more detail. As well, the relative importance of different physical mechanisms (in the ocean or atmosphere) has yet to be established. A seasonal dependence in predictability is seen in many models, but the processes responsible for it are not fully understood, and its meaning is still a matter of scientific discussion. Likewise, a marked decadal variation in skill is observed, and the reasons for this are still under investigation. Finally, the different prediction models yield similar skills, although they are initialized quite differently. The reasons for these differences are also unclear.

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.

Li, F. and J.-h. He (2000). "The decadal change of the interaction between northern Pacific SSTA and East Asian summer monsoon." Journal of Tropical Meteorology, Guangzhou, China 16(3): 260-271.

This paper analyzes mainly the relation between northern Pacific SSTA and east Asian summer monsoon. It is pointed out that their interaction has feature of change decadely. Before 1976 the northern Pacific SST anomalies acted on the east Asian summer monsoon by a great circle wavetrain, which causes northern-China precipitation abundance. After 1976 the northern Pacific SST anomalies make the wavetrain weak, relation to East Asian summer monsoon will be weak. It shows that the key region that affects east Asian summer monsoon is not changeless, it will divert from one area to another.

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.

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.

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. and M. Yanai (2002). "Influence of Eurasian spring snow cover on Asian summer rainfall." International Journal of Climatology 22(9): 1075-1089.

The Eurasian snow cover anomaly in spring has been considered as one of the important factors affecting Asian summer monsoon variability. Using the long time series (1922-98) of Eurasian spring (March-April) snow cover (ESSC) reconstructed by Brown and snow cover (1973-98) and depth (1979-87) data from satellite observation, the influences of ESSC on the all-India monsoon (June-September) rainfall (AIMR) and the summer rainfall over all parts of Asia are examined. It is found that the statistical relation between AIMR and ESSC changes over a multi-decadal time scale. The negative correlation between them has increased markedly since the mid 1970s. The region where the summer rainfall has the strongest and most stable negative correlation with the preceding ESSC is located in northern Mongolia, south of Lake Baikal. The correlation between the summer rainfall and ESSC increases after the data are treated with a low-pass filter, showing that the impact of snow cover may be seen more clearly with the removal of the effect of El Nino-southern oscillation. Comparative analyses for contrasting years with excessive and deficient snow cover show that the anomalies of ESSC occur mainly in northwestern Eurasia. In the years of excessive ESSC anomalies, cooling and a cyclonic circulation anomaly in the lower troposphere appear over the northern part of Eurasia, leading to a Rossby-wave-train-like circulation response, then a weakened East Asia summer monsoon and deficient rainfall with an anticyclonic circulation anomaly south of Lake Baikal. Anomalies with opposite signs occur in the years of deficient snow cover.

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

Meehl, G. A., J. M. Arblaster, et al. (2000). "Sea-ice effects on climate model sensitivity and low frequency variability." Climate Dynamics, Berlin, Germany 16(4): 257-271.

A change in a sea-ice parameter in a global coupled climate model results in a reduction in amplitude (of about 60%) and a shortening of the predominant period of decadal low frequency variability in the time series of globally averaged surface air temperature. These changes are global in extent and also are reflected in time series of area-averaged SSTs in the equatorial eastern Pacific Ocean, the principal components of the first EOFs of global surface air temperature and sea level pressure, Asian monsoon precipitations and other quantities. Coupled ocean-atmosphere-sea ice processes acting on a global scale are modified to produce these changes. Global climate sensitivity is reduced when ice albedo feedback is weakened due to the change in sea ice that makes it more difficult to melt. The changes in the amplitude and time scale of the low frequency variability in the model are traced to changes in the base state of the climate simulations as affected by modifications associated with the changes in sea ice. Making sea ice more difficult to melt results in increased sea-ice area, colder high latitudes, increased meridional surface temperature gradients, and, to a first order, stronger surface winds in most regions which strengthen near-surface currents, particularly in the Northern Hemisphere, and decreases the advection time scale in the upper ocean gyres. Additionally, in the North Atlantic there is enhanced meridional overturning due to increased density mainly in the Greenland Sea region. This also contributes to an intensified North Atlantic gyre. The changes in base state due to the sea ice change result in a more predominant decadal time scale of near 14 years and significantly reduced contributions from lower frequencies in the range of 15-40 year periods.

Meehl, G. A., W. M. Washington, et al. (2000). "Anthropogenic forcing and decadal climate variability in sensitivity experiments of twentieth- and twenty-first-century climate." Journal of Climate, Boston, MA 13(21): 3728-3744.

A methodology is formulated to evaluate the possible changes in decadal-timescale (10-20-yr period) surface temperature variability and associated low-frequency fluctuations of anthropogenic forcing and changes in climate base state due to the forcing in simulations of twentieth- and twenty-first-century climate in a global coupled climate model without flux adjustment. The two climate change experiments both start in the year 1900. The first uses greenhouse gas radiative forcing (represented by equivalent CO sub(2) ) observed during the twentieth century, and extends greenhouse gas forcing to the year 2035 by increasing CO sub(2) 1% yr super(-) super(1) compound after 1990 (CO sub(2) -only experiment). The second includes the same greenhouse gas forcing as the first, but adds the effects of time-varying geographic distributions of monthly sulfate aerosol radiative forcing represented by a change in surface albedo (CO sub(2) + sulfates experiment). The climate change experiments are compared with a 135-yr control experiment with no change in external forcing. Climate system responses in the CO sub(2) -only and CO sub(2) + sulfates experiments in this particular model are marked not only by greater warming at high latitudes in the winter hemisphere, but also by a global El Nino-like pattern in surface temperature, precipitation, and sea level pressure. This pattern is characterized by a relatively greater increase of SST in the central and eastern equatorial Pacific in comparison with the west, a shift of precipitation maxima from the western Pacific to the central Pacific, mostly decreases of Asian-Australian monsoon strength, lower pressure over the eastern tropical Pacific, deeper midlatitude troughs in the North and South Pacific, and higher pressure over Australasia. Time series analysis of globally averaged temperature and an EOF analysis of surface temperature are consistent with previous results in that enhanced low-frequency variability with periods greater than around 20 yr is introduced into the model coupled climate system with a comparable timescale to the forcing. To examine the possible effects of the associated changes in base state on decadal timescale variability (10-20-yr periods), the surface temperature time series are filtered to retain only variability on that timescale. The El Nino-like pattern of decadal variability seen in the observations is present in each of the model experiments (control, CO sub(2) only, and CO sub(2) + sulfates), but the magnitude decreases significantly in the CO sub(2) -only experiment. This decrease is associated with changes in the base-state climate that include a reduction in the magnitude (roughly 5%-20% or more) of wind stress and ocean currents in the upper 100 m in most ocean basins and a weakening of meridional overturning (about 50%) in the Atlantic. These weakened circulation features contribute to decreasing the amplitude of global decadal surface temperature variability as seen in a previous sea-ice sensitivity study with this model. Thus the superposition of low-frequency variability patterns in the radiative forcing increases climate variability for periods comparable to those of the forcing (greater than about 20 yr). However, there are decreases in the amplitude of future decadal (10-20-yr period) variability in these experiments due to changes of the base-state climate as a consequence of increases in that forcing.

Meehl, G. A., M. Wheeler, et al. (1994). "Low-frequency variability and CO sub(2) transient climate change. Part 3: Intermonthly and interannual variability." Climate Dynamics, Berlin, Germany 10(6-7): 277-303.

Components of interannual, intermonthly, and total monthly variability of lower troposphere temperature are calculated from a global coupled ocean-atmosphere general circulation model (GCM) (referred to as the coupled model), from the same atmospheric model coupled to a nondynamic mixed-layer ocean (referred to as the mixed-layer model), and from microwave sounding unit (MSU) satellite data. The coupled model produces most features of intermonthly and interannual variability compared to the MSU data, but with somewhat reduced amplitude in the extratropics and increased variability in the tropical western Pacific and tropical Atlantic. The relatively short 14-year period of record of the MSU data precludes definitive conclusions about variability in the observed system at longer time scales (e.g., decadal or longer). Different 14-year periods from the coupled model show variability on those longer time scales that were noted in Part 1 of this series. The relative contributions of intermonthly and interannual variability that make up the total monthly variability are similar between the coupled model and the MSU data, suggesting that similar mechanisms are at work in both the model and observed system. These include El Nino-Southern Oscillation (ENSO)-type interannual variability in the tropics, Madden-Julian Oscillation (MJO)-type intermonthly variability in the tropics, and blocking-type intermonthly variability in the extratropics. Manifestations of all of these features have been noted in various versions of the model. Significant changes of variability noted in the coupled model with doubled carbon dioxide differ from those in our mixed-layer model and earlier studies with mixed-layer models. In particular, in our mixed-layer model intermonthly and interannual variability changes are similar with a mixture of regional increases and decreases, but with mainly decreases in the zonal mean from about 20 degrees S to 60 degrees N and near 60 degrees S. In the coupled model, intermonthly and interannual changes of variability with doubled CO sub(2) show mostly increases of tropical interannual variability and decreases of intermonthly variability near 60 degrees N. These changes in the tropics are related to changes in ENSO, the south Asian monsoon, and other regional hydrological regimes, while the alterations near 60 degrees N are likely associated with changes in blocking activity. These results point to the important contribution from ENSO seen in the coupled model and the MSU data that are not present in the mixed-layer model.

Mehta, V. M. and K. M. Lau (1997). "Influence of solar irradiance on the Indian monsoon-ENSO relationship at decadal-multidecadal time scales." Geophysical Research Letters, Washington, DC 24(2): 159-162.

Munot, A. A. and D. R. Kothawale (2000). "Intra-seasonal, inter-annual and decadal scale variability in summer monsoon rainfall over India." International Journal of Climatology, Chichester, UK 20(11): 1387-1400.

Using daily rainfall data for the 30-year period of 1960-1989 and following an objective criterion, the pre-active, active and post-active phases of the summer monsoon (June-September) rainfall are clearly delineated for all-India and homogeneous regions of India. It is seen that on average, the monsoon is active for 103 days over northeast (NE-India) India, for 75-78 days over central-northeast (CNE-India) India and so on for all the regions. Average daily normal rainfall (ADNRF) is at a maximum of 14.7 mm over NE-India and at a minimum of 4.6 mm over NW-India. To investigate possible periodic oscillations in daily rainfall, the daily normal rainfall (DNRF) of all the regions is subjected to power spectrum analysis. This analysis reveals that DNRF exhibits periodicities of 5, 8-12 and 20 days over NE-India, about 5 and 40 days over WC-India, 8-12 and 40 days over NW-India and 8-10 and 40 days over PEN-India. Inter-annual and decadal scale variability of the summer monsoon rainfall over homogeneous regions is studied using the summer monsoon rainfall for the period of 1871-1990. It is discovered that summer monsoon rainfall of WC-India and NW-India is dominated by a quasi-biennial oscillation (QBO), whereas summer monsoon rainfall of NE-India and PEN-India is dominated by ENSO-type periodicities. Epochs of increasing and decreasing rainfall are also observed in the summer monsoon rainfall over homogeneous regions of India.

Nakamura, H., T. Izumi, et al. (2002). "Interannual and Decadal Modulations Recently Observed in the Pacific Storm Track Activity and East Asian Winter Monsoon." Journal of Climate 15(14): 1855-1874.

Interannual variability of the North Pacific storm track observed over 17 recent winters is documented. The local storm track activity is measured by a meridional flux of sensible heat associated with the lower-tropospheric subweekly fluctuations. The interannual variability in the heat flux over the northwestern (NW) Pacific is found to be strongest in midwinter. The first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the NW Pacific, in association with the decadal weakening of the east Asian winter monsoon (Siberian high) and the Aleutian low that occurred in the late 1980s. The most marked signature of this enhancement is that the midwinter minimum in the storm track activity, which had been apparent in the early to mid-1980s, almost disappeared afterward. As opposed to linear theory of baroclinic instability, the enhanced activity occurred despite the weakening of the Pacific jet. As the excessively strong westerlies weakened, the eddy temperature field tended to become better correlated with the eddy meridional and vertical velocities, suggesting that eddy structure tends to become more efficient in converting the mean-flow available potential energy into eddy kinetic energy for growth. The weakened jet also acted to prolong the residence time for migratory eddies in the baroclinic zone, which seemingly overcompensated the effect of the reduced mean-flow baroclinicity but appeared to be of secondary importance. Over the Far East, tropospheric warming to the north of the weakened jet appears to be associated with an anomalous overturning in the thermally direct sense, which is not attributable to the feedback from the concomitant enhancement in the local storm track activity. Over the NW Pacific, the enhanced poleward heat transport by the intensified storm track tended to be compensated by the reduced transport by the weakened monsoonal flow, leaving rather small anomalies in the net transport. Also over the NW Pacific, the weakened monsoonal flow and enhanced storm track activity since the late 1980s led to the reduction in the evaporation and associated latent heat release from the ocean surface and increased precipitation, respectively. The resultant anomalous moisture deficit was compensated by the anomalous moisture transport from the northeastern Pacific, where the enhanced evaporation and reduced precipitation gave rise to an anomalous moisture surplus.

Nitta, T. (1996). "Decadal variations in atmosphere and ocean." Umi to Sora [Sea and Sky.], Kobe, Japan 71(3): 81-87.

Decadal variations of the atmosphere-ocean system are analyzed based on sea surface temperature, surface pressure, surface wind, tropical precipitation and Northern Hemisphere 500-hPa height data. It is found that there exist two types of decadal-scale variations which mainly occurs in the Pacific Ocean and in the Atlantic Ocean, respectively. Large variations took place during the period from 1970s and 1980s corresponding to the former variation in which SST in the tropical central and eastern Pacific increased, precipitation also increased over that area, east-west circulations in the tropics were weakened, monsoon circulations in the east Asia were intensifies and Pacific-North America (PNA) pattern was intensified. Corresponding to the latter variation, large changes of SST were found in the Atlantic Ocean around 1970 and an atmospheric teleconnection pattern can be seen from the Atlantic Ocean to the Europe.

Parthasarathy, B. (1991). "Indian monsoon variability." WMO Tropical Meteorology Research Programme 183.

Atmospheric circulation including monsoon circulation shows fluctuations on various time scales. Two main aspects of the monsoon variability will be discussed here, namely (i) intraseasonal and (ii) interannual scale. The complex and pulsatory character of the southwest (summer) monsoon is well known. It is brought out by many scientists that oscillations of type (a) 5-7 days, (b) 10-15 days and (c) 30-60 days are prominent among these. The details of these oscillations and their spatial temporal characteristics will be discussed. The interannual and decadal variability of the Indian summer monsoon is an important aspect to be studied and understood. The behaviour of the Indian summer monsoon during the last 120 years (1871-1990) will be presented and discussed. These variations of monsoon may be linked with the conditions over Asian/Indian Ocean and Pacific regions.

Parthasarathy, B., K. Rupa Kumar, et al. (1992). "Indian summer monsoon rainfall indices: 1871-1990." Meteorological Magazine, London, England 121(1441): 174-186.

The Indian summer monsoon rainfall, because of its importance to the country's economy and in the global atmospheric circulation, has motivated many studies pertaining to its behavior, characteristics, teleconnections with global/regional features and long-range prediction. These studies have used various types of rainfall series, most of them based on a variable network of rain-gauges, with the consequent inhomogeneities in the data series. This paper describes some homogenous representations of the Indian summer monsoon rainfall for the period 1871-1990, prepared on the basis of a fixed and well-distributed network of 306 rain-gauges. An Indian Summer Monsoon Rainfall (ISMR) Index, indicating the net excess or deficient rainfall conditions over the country, is proposed. This index, and some others are listed in the papers, for ready use in the studies of monsoon, its teleconnections and other related aspects. Statistical analysis of the above series identifies 18 large-scale dry years and 15 large-scale wet years during the last 120 years. The decadal means of ISMR index were continuously negative for three decades 1901-30, positive 1931-60 and again became negative during the current period 1961-90.

Parthasarathy, B., K. Rupa Kumar, et al. (1993). "Homogeneous Indian monsoon rainfall: variability and prediction." Proceedings, Bangalore, India 102(1): 121-155.

The Indian summer monsoon rainfall is known to have considerable spatial variability, which imposes some limitations on the all-India mean widely used at present. To prepare a spatially coherent monsoon rainfall series for the largest possible area, fourteen subdivisions covering the northwestern and central parts of India (about 55% of the total area of the country), having similar rainfall characteristics and associations with regional /global circulation parameters are merged and their area-weighted means computed, to form monthly and seasonal homogeneous Indian monsoon (HIM) rainfall series for the period 1871-1990. This paper includes a listing of monthly and seasonal rainfall of HIM region. HIM rainfall series has been statistically analysed to understand its characteristics, variability and teleconnections for long-range prediction. HIM rainfall series is found to be homogeneous, Gaussian distributed and free from persistence. The mean (R) rainfall is 757 mm (87% of annual) and standard deviation (S) 119 mm, with a coefficient of variation (CV) of 16%. There were 21 dry (R sub(i) less than or equal to R-S) and 19 wet (R sub(i) greater than or equal to R+S) years during 1871-1990. There were clusters of frequent negative departures during 1899-1920 and 1965-1987 and positive departures during 1942-1961. The recent three decades show very high rainfall variability with 10 dry and 6 wet years. The decadal averages were alternatively positive and negative for three consecutive decades, viz., 1871-1900 (positive); 1901-1930 (negative); 1931-1960 (positive) and 1961-1990 (negative) respectively. Significant QBO and autocorrelation at 14th lag have been found in HIM rainfall series. To delineate the changes in the climatic regime of the Indian summer monsoon, sliding correlation coefficients (CCs) between HIM rainfall series and (i) Bombay msl pressure, (ii) darwin msl pressure and (iii) Northern Hemisphere surface air temperature over the period 1871-1990 have been examined. The 31-year sliding CCs showed the systematic turning points of positive and negative CCs around the years, 1900 and 1940. In the light of other corroborative evidences, these turning points seem to delineate `meridional' monsoon regime during 1871-1900 and 1940-1990 and `zonal' monsoon regime during 1901-1940. The monsoon signal is particularly dominant in many regional and global circulation parameters, during 1951-1990. Using the teleconnections of HIM series with 12 regional/global circulation parameters during the recent 36-year period 1951-86 regression models have been developed for long-range prediction. In the regression equations 3 to 4 parameters were entered, explaining up to 80% of the variance, depending upon the data period. The parameters that prominently enter the multiple regression equations are (i) Bombay msl pressure, (ii) April 500 mb Ridge at 75 degrees E, (iii) NH temperature, (iv) Nouvelle minus Agalega msl pressure and (v) South American msl pressure. Eleven circulation parameters for the period 1951-80 were subjected to principal component analysis (PCA) and the PC's were used in the regression model to estimate HIM rainfall. The multiple regression with three PCs explain 72% of variance in HIM rainfall.

Patwardhan, S. K. and H. N. Bhalme (2001). "A study of cyclonic disturbances over India and the adjacent ocean." International Journal of Climatology, Chichester, UK 21(4): 527-534.

Annual and seasonal frequencies of cyclonic disturbances that occurred over the area extending from 5 degrees N to 30 degrees N and 50 degrees E to 100 degrees E are examined for the period 1891-1998. The analysis revealed a significant decreasing trend in annual as well as seasonal frequency of cyclonic disturbances in the monsoon season, The frequency of cyclonic distrubances in the monsoon season also shows the typical quasi-biennial oscillation. On the decadal time scale, frequencies in the monsoon season, as well as annual cyclonic disturbances, show a decreasing trend.

Qian, W. and Y. Zhu (2001). "Climate Change in China from 1880 to 1998 and its Impact on the Environmental Condition." Climatic Change 50(4): 419-444.

The global mean surface air temperature (SAT) or the Northern Hemisphere mean SAT has increased since the late nineteenth century, but the mean precipitation around the world has not formed a definite tendency to increase. A lot of studies showed that different climate and environmental changes during the past 100 years over various regions in the world were experienced. The climate change in China over the past 100 years and its impact on China's environmental conditions needs to be investigated in more detail. Data sets of surface air temperature and atmospheric precipitation over China since 1880 up to the present are now available. In this paper, a drought index has been formulated corresponding to both the temperature and precipitation. Based on three series of temperature, precipitation, and drought index, interdecadal changes in all 7 regions of China and temperature differences among individual regions are analyzed. Some interesting facts are revealed using the wavelet transform method. In Northeast China, the aridification trend has become more serious since 1970s. Drought index in North China has also reached a high value during 1990s, which seems similar to that period 1920s-1940s. In Northwest China, the highest temperature appeared over the period 1930s-1940s. Along the Yangtze River valley in central eastern China and Southwest China, interdecadal high temperature occurred from 1920s to 1940s and in 1990s, but the drought climate mainly appeared from 1920s to early 1940s. In South China, temperature remained at a high value over the period 1910s-1940s, but the smaller-scale variation of drought index was remarkable from 1880 to 1998. Consequently, the quasi-20-year oscillation (smaller-scale variation) and the quasi-70-year oscillation (secular variation) obviously exist in temperature and precipitation series in different regions over China. Climate change and intensified human activity in China have induced certain environmental evolutions, such as the frequency change of dust-storm event in northern China, no-flow in the lower reaches of the Yellow River and the runoff variation in Northwest China. On the other hand, frequent floods along the Yangtze River and high frequency of drought disaster have resulted in tremendous economic losses in the last decade in China. The primary reason for these happenings may be attributed to the evolution of the monsoon system in East Asian.

Qian, W. and Y. Zhu (2002). "Little Ice Age Climate near Beijing, China, Inferred from Historical and Stalagmite Records." Quaternary Research 57(1): 109-119.

Four data sets yield information about Holocene climatic change in China at different scales of space and time: (a) 120-yr ground temperature and precipitation measurements covering eastern China; (b) two NOAA 10-yr 850 hPa wind records that highlight features of data set a; (c) an 1100-year record of annual calcite accumulation on a stalagmite near Beijing, and (d) Lamb-type average wetness and temperature data from Chinese historical records back to A.D. 1470 and 1450, respectively. Dry-wet fluctuations and cold-warm oscillations are inferred using the long-term stalagmite thickness series. Quasi-70, 140, 450, and 750-yr oscillations have been detected using a wavelet transform technique. A phase relationship between temperature and precipitation oscillations has been identified based on modern observations and historical records. In northern China, relatively lower temperatures correlate with periods when precipitation shifted from above to below normal. Three colder periods during the Little Ice Age (LIA) in China are inferred, centered in the late 14th century (750-yr oscillation), the early 17th century (450-yr), and the 19th century (140-yr). The latest cool period (1950s-1970s) is found at the 70-yr oscillation. Interdecadal drought-flood and cold-warm differences are explained using modern circulation patterns. LIA climate in China was likely controlled by East Asian monsoon circulation anomalies that were affected by variations in continent-ocean thermal contrast.

Rajeevan, M., R. K. Prasad, et al. (2001). "Cloud climatology of the Indian Ocean based on ship observations." Mausam 52(3): 527-540.

Surface cloud data based on synoptic observations made by Voluntary Observing Ships (VOS) during the period 1951-98 were used to prepare the seasonal and annual cloud climatology of the Indian Ocean. The analysis has been carried out by separating the long-term trends, decadal and inter-annual components from the monthly cloud anomaly time series at each 5 degree x 5 degree grids. Maximum zone of total and low cloud cover shifts from equator to northern parts of India during the monsoon season. During the monsoon season (June-September), maximum total cloud cover exceeding 70% and low cloud cover exceeding 50% are observed over north Bay of Bengal. Maximum standard deviation of total and low cloud cover is observed near the equator and in the southern hemisphere. Both total and low cloud cover over Arabian Sea and the equatorial Indian Ocean are observed to decrease during the ENSO events. However, cloud cover over Bay of Bengal is not modulated by the ENSO events. On inter-decadal scale, low cloud cover shifted from a "low regime" to a "high regime" after 1980 which may be associated with the corresponding inter-decadal changes of sea surface temperatures over north Indian Ocean observed during the late 1970s.

Rao, D. V. B., C. V. Naidu, et al. (2001). "Trends and fluctuations of the cyclonic systems over North Indian Ocean." Mausam 52(1): 37-46.

The data of the monthly cyclone frequencies over North Indian Ocean for the period 1877-1998 has been analysed to study the long-term trends and fluctuations. Analysis has been made separately for depressions and cyclones for the pre-monsoon, monsoon and post-monsoon seasons along with the annual frequencies. The data was subjected to 11-year moving averages and the epochs of increasing and decreasing trends have been identified. A consistent decreasing trend after 1950s is a notable feature. The time series of the monthly cyclone frequency were passed through a high-pass filter to eliminate periods greater than 21 years and then subjected to spectrum analysis using Maximum Entropy Method to obtain dominant periodicities. Three significant periodicities at 2.2-2.8; 3.5-6.5 and 10-15 years have been identified which could be attributed to QBO, ENSO and decadal frequencies.

Rasmusson, E. M., X. Wang, et al. (1995). "Secular variability of the ENSO cycle." National Research Council, et al., Natural climate variability on decade to century time scales., Washington, D.C., National Academy Press.

Secular changes can occur in both multi-decadal climate means and multi-decadal measures of variability. We have examined the secular variability of the ENSO cycle as revealed by commonly used indices, i.e., sea level pressure and sea surface temperature from the low-latitude core region of the oscillation. We view the low-frequency variations (periods longer than approximately 30 years) as a varying base state upon which the ENSO cycle is superimposed. The following are the major findings of the analyses: ENSO-cycle variance for 31-year periods has changed by a factor of two or more during the past century. The cycle was quite pronounced late in the nineteenth century, was relatively weak from 1920 to 1950, and has increased in intensity since then. The century-scale variation in equatorial sea surface temperature was broadly similar to that in globally averaged sea surface temperature. No obvious relationship could be detected between variations in the base-state parameters we analyzed (equatorial sea surface temperature and Pacific-Indian Ocean sector sea level pressure) and variations in the intensity of the ENSO cycle. Regional statistics, such as those derived from the Quinn et al. (1987) compilation of strong and very strong El Nino events in Peru, cannot be considered a reliable index of basin-scale ENSO-cycle variability. The century-scale variations in ENSO-cycle intensity broadly correspond to changes in all-India monsoon-season rainfall variability, to the modulation of the intensity of drought episodes over the U.S. Great Plains during the twentieth century, and, less clearly, to the century-scale variation in Sahel rainfall.

Sahai, A. K., M. K. Soman, et al. (2000). "All India summer monsoon rainfall prediction using an artificial neural network." Climate Dynamics, Berlin, Germany 16(4): 291-302.

The prediction of Indian summer monsoon rainfall (ISMR) on a seasonal time scales has been attempted by various research groups using different techniques including artificial neural networks. The prediction of ISMR on monthly and seasonal time scales is not only scientifically challenging but is also important for planning and devising agricultural strategies. This article describes the artificial neural network (ANN) technique with error- back-propagation algorithm to provide prediction (hindcast) of ISMR on monthly and seasonal time scales. The ANN technique is applied to the five time series of June, July, August, September monthly means and seasonal mean (June + July + August + September) rainfall from 1871 to 1994 based on Parthasarathy data set. The previous five years values from all the five time-series were used to train the ANN to predict for the next year. The details of the models used are discussed. Various statistics are calculated to examine the performance of the models and it is found that the models could be used as a forecasting tool on seasonal and monthly time scales. It is observed by various researchers that with the passage of time the relationships between various predictors and Indian monsoon are changing, leading to changes in monsoon predictability. This issue is discussed and it is found that the monsoon system inherently has a decadal scale variation in predictability.

Shankar, D. and S. R. Shetye (1999). "Are interdecadal sea level changes along the Indian coast influenced by variability of monsoon rainfall?" Journal of Geophysical Research, Washington, DC 104(C11): 26031-26042.

The Mumbai (Bombay) tide gauge data, the only century-long record in the Indian Ocean, show that interdecadal changes in sea level mimic those in rainfall over the Indian subcontinent. We propose that the link between rainfall and sea level arises from changes in salinity in coastal waters. Rivers fed by southwest monsoon (June-September) rainfall bring a large fraction of the runoff to the Bay of Bengal, from where it is transported to the west coast of India by an equatorward East India Coastal Current, which is triggered partly by the withdrawal of the southwest monsoon. The West India Coastal Current carries the low-salinity water from the bay as well as the runoff from local rivers northward. The advection of the riverine inflow to Mumbai occurs within a season, but the slow mixing in the ocean forces changes in the cross-shore density gradient on longer timescales. This density gradient forces a two-layer geostrophic circulation, with a surface current, which flows with the lighter water on its right, and an undercurrent. Lower (higher) salinity at the coast implies higher (lower) coastal sea level and a rise (fall) of the pycnocline at the coast. Thus the interdecadal variability of sea level along the Indian coast can be linked directly to the variability of the monsoon, the major aspect of the climate of the region, but by a mechanism that is different from those generally proposed to link sea level to climate change; these hypotheses usually invoke a change in volume because of global warming.

Sheppard, P. R., A. C. Comrie, et al. (2002). "The climate of the US Southwest." Climate Research 21(3): 219-238.

This paper summarizes the current state of knowledge of the climate of southwest USA (the `Southwest'). Low annual precipitation, clear skies, and year-round warm climate over much of the Southwest are due in large part to a quasi-permanent subtropical high-pressure ridge over the region. However, the Southwest is located between the mid-latitude and subtropical atmospheric circulation regimes, and this positioning relative to shifts in these regimes is the fundamental reason for the region's climatic variability. Furthermore, the Southwest's complex topography and its geographical proximity to the Pacific Ocean, the Gulf of California, and the Gulf of Mexico also contribute to this region's high climatic variability. El Nino, which is an increase in sea-surface temperature of the eastern equatorial Pacific Ocean with an associated shift of the active center of atmospheric convection from the western to the central equatorial Pacific, has a well-developed teleconnection with the Southwest, usually resulting in wet winters. La Nina, the opposite oceanic case of El Nino usually results in dry winters for the Southwest. Another important oceanic influence on winter climate of the Southwest is a feature called the Pacific Decadal Oscillation (PDO), which has been defined as temporal variation in sea-surface temperatures for most of the Northern Pacific Ocean. The effects of ENSO and PDO can amplify each other, resulting in increased annual variability in precipitation over the Southwest. The major feature that sets the climate of the Southwest apart from the rest of the United States is the North American monsoon, which in the US is most noticeable in Arizona and New Mexico. Up to 50% of the annual rainfall of Arizona and New Mexico occurs as monsoonal storms from July through September. Instrumental measurement of temperature and precipitation in the Southwest dates back to the middle to late 1800s. From that record, average annual rainfall of Arizona is 322 mm (12.7"), while that of New Mexico is 340 mm (13.4"), and mean annual temperature of New Mexico is cooler (12szC [53szF]) than Arizona (17szC [62szF]). As instrumental meteorological records extend back only about 100 to 120 yr throughout the Southwest, they are of limited utility for studying climate phenomena of long time frames. Hence, there is a need to extend the measured meteorological record further back in time using so-called `natural archive' paleoclimate records. Tree-ring data, which provide annual resolution, range throughout the Southwest, extend back in time for up to 1000 yr or more in various forests of the Southwest, and integrate well the influences of both temperature and precipitation, are useful for this assessment of climate of the Southwest. Tree growth of mid-elevation forests typically responds to moisture availability during the growing season, and a commonly used climate variable in paleo-precipitation studies in the Palmer Drought Severity Index (PDSI), which is a single variable derived from variation in precipitation and temperature. June-August PDSI strongly represents precipitation and, to a lesser extent, temperature of the year prior to the growing season (prior September through current August). The maximum intra-ring density of higher elevation trees can yield a useful record of summer temperature variation. The combined paleo-modern climate record has at least 3 occurrences of multi-decadal variation (50 to 80 yr) of alternating dry (below average PDSI) to wet (above average PDSI). The amplitude of this variation has increased since the 1700s. The most obvious feature of the temperature record is its current increase to an extent unprecedented in the last 400 yr. Because this warming trend is outside the variation of the natural archives, it is possible that anthropogenic impacts, such as increased atmospheric concentrations of greenhouse trace gases, are playing a role in climate of the Southwest. Accordingly, this pattern merits further research in search of its cause or combination of causes.

Shi, N. (1996). "Features of the east Asian winter monsoon intensity on multiple time scale in recent 40 years and their relation to climate." Quarterly Journal of Applied Meteorology, Beijing, China 7(2): 175-182.

Utilizing the east Asian monsoon intensity indexes the features of their trend, interannual and interdecadal changes of the monsoon in January during the period of 1950 similar to 1989 and their relation to China's winter weather-climate are studied. It is found that the interannual and interdecadal changes of the east Asian winter monsoon were closely related to the weather in China. It was cold /dry when the winter monsoon was strong, and warm/moist weather when the monsoon was weak. However, the relationship between the monsoon and China's climate change trend was not as good as that of the interannual and interdecadal changes. During the past 40 years, the air temperature experienced a remarkable increase, while the monsoon underwent a pronounced reduction. Since the mid-1980s, however, the winter monsoon has become rather weakened. It is also found that when the east Asian winter monsoon was strong, the atmospheric circulation showed the strong WP pattern and the EU teleconnection pattern.

Shi, N., J. Lu, et al. (1996). "East Asian winter/summer monsoon intensity indices with their climatic change in 1873-1989." Journal of Nanjing Institute of Meteorology, Nanjing, China 19(2): 168-177.

Defined are east Asian winter/summer monsoon intensity indices and calculated 1873-1989 winter/summer and monthly (JJA/DJF) indices with the secular climatic change investigated. Evidence suggests that the summer monsoon was greatly enhanced for the study period with little change or even slightly enfeebled for the winter wind. Also, analysis shows that the summer monsoon displayed enhanced sudden change around 1918 concurrently with the abrupt rise in northern summer surface temperature, and, in contrast, the winter monsoon showed less noticeable abrupt change in 1958. Finally, sliding correlation analysis was made to investigate the relation between the winter/summer monsoons and northern surface temperature, indicating an interdecadal variation in their correlation.

Shi, N. and Y. Yang (1998). "Main characteristics of East Asian summer/winter monsoon index for 1873-1996." Journal of Nanjing Institute of Meteorology, Nanjing, China 21(2): 208-214.

The East Asian summer and winter monsoon intensity indices are constructed by using the SLP data for the period of 1873-1997 and their interannual and inter-decadal variabilities are analyzed. The results show that summer and winter weather/climate over China are closely related to the monsoon intensity indices and The East Asian summer monsoon intensity has a positive relationship with the Indian monsoon, and their intensities manifest quasi-biennial oscillations.

Shi, N. and Q. Zhu (1996). "Anomalous east Asian winter monsoon intensity and its relation to summer 500 hPa atmospheric circulation and climate anomaly in China." Journal of Tropical Meteorology, Guangzhou, China 12(1): 26-33.

In this paper, studies are made of the east Asian winter monsoon intensity and its relation to the summer 500 hPa atmospheric circulation and the large-scale climate anomaly in China by using the east Asian winter monsoon intensity data for the period of 1951-1990. It is found that in the years with a weak winter monsoon, there exists a positive-negative-positive anomalous distribution. It is a weak EAP telecorrelation pattern at 500 hPa in summer that extends from the South China Sea, the Philippines through the Yellow Sea, the Sea of Japan and the Sea of Okhotsk. This anomalous distribution causes increases of rainfall over the the reaches of Yantze and Huaihe rivers and decreases of rainfall in south and north China during the summertime. It is also shown that in the past 40 years the interdecadal change of summer rainfall over the above two river reaches is closely related to that of the winter intensity in previous years.

Shrestha Arun, B., C. P. Wake, et al. (2000). "Precipitation fluctuations in the Nepal Himalaya and its vicinity and relationship with some large scale climatological parameters." International Journal of Climatology, Chichester, UK 20(3): 317-327.

Precipitation records from 78 stations distributed across Nepal were analysed and all-Nepal (1948-1994) and subregional records (1959-1994) were developed. The all-Nepal and regional precipitation series showed significant variability on annual and decadal time scales. Distinct long-term trends were not found in these precipitation records. The all-Nepal record agrees well with the precipitation records from northern India, while it does not compare well with the all-India precipitation record. The all-Nepal monsoon record is highly correlated with the Southern Oscillation Index (SOI) series. The exceptionally dry year of 1992 recorded in Nepal coincides with the elongated El Nino of 1992-1993 and the Mount Pinatubo eruption. A remarkable cooling in the region covering the Tibetan Plateau also occurred in 1992, suggesting that Pinatubo aerosol played a major role in the drought of that particular year in Nepal. In other years, the correlation between the precipitation record from Nepal and the temperature of the Tibetan Plateau is not significant, while a stronger correlation with temperature over the Indian Ocean and southern India exists. This provides further support for the strong relationship between the El Nino-Southern Oscillation (ENSO) and precipitation fluctuation in Nepal. The correlation is stronger between all-Nepal monsoon precipitation and SOI averaged over seasons following the monsoon compared with seasons preceding the monsoon.

Sikka, D. R. (1991). "Monsoon and ENSO." WMO Tropical Meteorology Research Programme.

The relationship between ENSO and monsoon variability, particularly the Indian summer monsoon, is discussed. Every few years (average interval c. 4 years) the warming associated with the El Nino current becomes unusually strong, with disastrous weather over the coast of South America. The atmospheric counterpart of El Nino is the Southern Oscillation (SO) which relates to the interannual variations of near global scale pressure. Correlations between monthly SO index and all of Indian monsoon rainfall are negative in the early part of the year and change sign by April, after which they continually increase until the end of the year. Similar correlations are found between Indian monthly rainfall and three monthly SO indices, namely, Darwin surface pressure, equatorial Pacific SST, and equatorial Pacific rainfall. An examination of the relationship between El Nino and Indian monsoon rainfall reveals an average percentage departure of rainfall of -11% for ENSO years, and 5.7% for Anti-ENSO years. ENSO years also show a relationship with monsoon rainfall on a decadal time scale, with the epochs of dry (wet) years showing higher (lower) frequency of occurrence of ENSO years. It is concluded that the Indian monsoon is significantly influenced by ENSO events, but that the phasing of the ENSO events is such that only small, though significant, variability of monsoon rainfall can be explained by ENSO-related parameters observed in the previous winter or spring.

Sugimoto, T., S. Kimura, et al. (2001). "Impact of El Nino events and climate regime shift on living resources in the western North Pacific." Progress in Oceanography 49(1-4): 113-127.

Features of El Nino events and their biological impacts in the western North Pacific are reviewed, focusing on interactions between ENSO and the East Asian monsoon. Impacts of El Nino on the climate in the Far East become evident as 'cool summers and warm winters'. Effects of climate regime shift on ENSO activities, western boundary currents and upper-ocean stratification, as well as their biological consequences are summarized. These have been: In the western equatorial Pacific, an eastward extension of the warm pool associated with El Nino events induces an eastward shift of main fishing grounds of skip jack and big eye tunas. The surface salinity front in the North Equatorial Current region retreats southward, associated with El Nino events. This leads to a southward shift of the spawning ground of Japanese eel, which is responsible for a reduction in the transport of the larval eels to the Kuroshio and Japanese coastal region, causing poor recruitment. Intensification of winter cooling and vertical mixing associated with La Nina (El Nino) events in the northern subtropical region of the western (central) North Pacific reduces surface chlorophyll concentration levels and larval feeding condition for both Japanese sardines and the autumn cohort of Neon squid during winter-early spring. The semi-decadal scale calm winter that occurred during the early 1970s triggered the first sharp increase of sardine stock around Japan. A remarkable weakening of southward intrusion of the Oyashio off the east coast of Japan during 1988-91, resulted in a decrease in chlorophyll concentrations and mesozooplankton biomass in late spring-early summer of the Kuroshio-Oyashio transition region. Changes occurred in the dominant species of small pelagic fish, through successive recruitment failures of Japanese sardine.

Sun, X., L. Chen, et al. (2001). "Interannual variation of index of East Asian land-sea thermal difference and its relation to monsoon circulation and rainfall over China." Acta Meteorologica Sinica, Beijing, China 15(1): 71-85.

This paper proposes an index of land-sea thermal difference (ILSTD) that describes its zonal and meridional strength responsible for East Asian monsoon circulation to study its relation to the East Asian monsoon circulation and the summer rainfall over China on an interannual basis. Results are as follows: (1) ILSTD can be used to measure the strength of East Asian summer monsoon in such a way that the strong (weak) ILSTD years are associated with strong (weak) summer monsoon circulation. (2) The index also reflects well summer rainfall anomaly over the eastern part of China. In the strong index years, rain belt is mainly located over the northern China, and serious drought emerges in the Jianghuai valleys and mid-lower reaches of the Changjiang River, along with increase of rainfall in North and South China, but in the weak years it is contrary. (3) Besides, the index has obvious QBO and quasi-4-year oscillations, but the periods and amplitudes have significant changes on an interdecadal basis.

Terray, P. (1994). "An evaluation of climatological data in the Indian Ocean area." Journal of the Meteorological Society of Japan, Tokyo, Japan 72(3): 359-386.

This paper presents evidence that both land-records and marine products currently used to assess the interannual and decadal variability of the monsoon system are subjected to important systematic errors due to non-climatic factors. The main inhomogeneities in the NCAR's World Monthly Surface Climatology during the 1900-1984 period affect all sea level pressure (SLP) time series over the Indian subcontinent. These discontinuities are mainly linked to the non-consideration of changes in the time of observation between sample periods when the data have been compiled at NCAR. The main example of such discontinuity is observed in 1961 with the change from the World Weather Records collection to the Monthly Climatic Data for the World series. Systematic biases are also revealed for sea surface temperature (SST), air temperature (ART) and SLP ship measurements compiled over the Indian Ocean during 1900-1986. The main spurious jumps occur around 1932 for SLP, 1940 for both SST and ART, and 1954 for SST sampled in the east Arabian Sea and the Bay of Bengal. In addition, an artificial trend contaminates SST reports during 1954-1976. Though no attempts have been made to determine the exact causes responsible for these inhomogeneities, there is little doubt about their origins because all these dates and trends are in phase with important changes in the composition of ``source-decks'' merged into the marine dataset, and do not agree with fluctuations of corrected SLP and temperature measurements along the coasts of the Indian subcontinent. Finally, substantial biases in resolution of the annual cycle can be expected for all the parameters because the sampling over the Indian Ocean has a strong seasonal dependence after 1950. Many inconsistencies in the observational picture of interannual SST variations over the Indian Ocean are thought to be linked to such data problems. A comparison between land and marine trends has however suggested the existence of some significant decadal-scale fluctuations in the Indian region during the 1900-1986 period. These true climatic happenings include prominently a warming temperature trend and a general SLP decrease over both land and ocean during 1900-1939, and a sudden warming in the Indian Ocean after 1976. This recent warming does not affect the interior of the Indian subsontinent and is in phase with persistent positive SLP anomalies for the whole Indian sector. This corroborates the evidence of a climatic change in the Indian Ocean after 1976 (Nitta and Yamada, 1989).

Torrence, C. and P. J. Webster (1998). "The annual cycle of persistence in the El Nino/Southern Oscillation." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 124(550, Pt. B): 1985-2004.

A spring `predictability barrier' exists in both data and models of the El Nino/Southern Oscillation (ENSO) phenomenon. In statistical analyses this barrier manifests itself as a drop-off in monthly persistence (lagged correlation) while in coupled ocean-atmosphere models it appears as a decrease in forecast skill. The `persistence barrier' for ENSO indices is investigated using historical sea surface temperature and sea-level pressure data. Simple statistical models are used to show that the persistence barrier occurs because the boreal spring is the transition time from one climate state to another, when the `signal-to-noise' of the system is lowest and the system is most susceptible to perturbations. The strength of the persistence barrier is shown to depend on the degree of phase locking of the ENSO to the annual cycle. The phase locking of the ENSO to the annual cycle, as well as the ENSO variance, is shown to vary on interdecadal time-scales. During 1871-1920 and 1960-90 the ENSO variance was high, while during 1920-50 it was low. Using wavelet analysis, this interdecadal variability in ENSO is shown to be correlated with changes in Indian summer monsoon strength. Finally, the change in persistence-barrier strength between 1960-79 and 1980-95 is related to changes in the phase locking of ENSO to the annual cycle. These changes in persistence and phase locking appear to be related to the increased forecast skill seen from recent coupled ocean-atmosphere models.

Torrence, C. and P. J. Webster (1999). "Interdecadal changes in the ENSO-monsoon system." Journal of Climate, Boston, MA 12(8, Pt. 2): 2679-2690.

The El Nino-Southern Oscillation (ENSO) and Indian monsoon are shown to have undergone significant interdecadal changes in variance and coherency over the last 125 years. Wavelet analysis is applied to indexes of equatorial Pacific sea surface temperature (Nino3 SST), the Southern Oscillation index, and all-India rainfall. Time series of 2-7-yr variance indicate intervals of high ENSO-monsoon variance (1875-1920 and 1960-90) and an interval of low variance (1920-60). The ENSO-monsoon variance also contains a modulation of ENSO-monsoon amplitudes on a 12-20-yr timescale. The annual-cylcle (1 yr) variance time series of Nino3 SST and Indian rainfall is negatively correlated with the interannual ENSO signal. The 1-yr variance is larger during 1935-60, suggesting a negative correlation between annual-cycle variance and ENSO variance on interdecadal timescales. The method of wavelet coherency is applied to the ENSO and monsoon indexes. The Nino3 SST and Indian rainfall are found to be highly coherent, especially during intervals of high variance. The Nino3 SST and Indian rainfall are approximately 180 degrees out of phase and show a gradual increase in phase difference versus Fourier period. All of the results are shown to be robust with respect to different datasets and analysis methods.

Verma, R. K. (1986). "Predictive relationship between Northern Hemispheric surface air temperature and Indian summer monsoon." World Meteorological Organization, Geneva, Programme on Long-Range Forecasting Research, Report Series 1986 2(6): 798-806.

The predictive relationship between Northern Hemispheric air temperature variations and long-term variability of the summer monsoon is investigated in order to provide long-term forecasts of the climatic behavior of the monsoon on a decadal scale and seasonal rainfall activity on an interannual scale. Summer monsoon seasonal rainfall of India from June through Sept., and Northern Hemispheric series of air temperature for the same period were used. With the aid of data presented in graphs and tables, the long-term (decadal) variability of temperature and summer monsoon rainfall, the long-term (decadal) relationship between these parameters, the interannual variability of the monsoon in relation to the Northern Hemispheric variations, and the prediction of monsoon rainfall are discussed. The analysis reveals that the temperature anomalies influence the monsoon on a decadal and interannual scale. On decadal and longer time scales, the periods of relatively cooler or unstable climate over the Northern Hemisphere (1901-1920 and 1960-1980) were associated with less than normal monsoon rainfall, greater rainfall variability, and greater frequency of monsoon failures. The relatively warmer and more stable climatic period of 1921-1960 was associated with favorable monsoon activity, above-average monsoon rainfall, smaller variability, and very low frequency of monsoon failure. On the interannual scale, there was a high positive correlation between Jan. and Feb. temperature anomalies and the ensuing summer monsoon; the relationship was most evident during the period 1951-1980 and was strongest with the failure of monsoons. The significantly cooler winter months (Jan.-Feb.) over the Northern Hemisphere affect the forthcoming monsoon rainfall adversely. This relationship provides a potential predictor for long-range forecasting of monsoon rainfall over India, 3 mo in advance, particularly of its failure, leading to large-scale drought conditions.

Verma, R. K. (1990). "Recent monsoon variability in the global climate perspective." Mausam, New Delhi, India 41(2): 315-320.

Over the past few years the Indian summer monsoon has shown large abnormalities, perhaps more than that observed in any period on the same time-scale. The decadal scale mean rainfall has been continually decreasing since the decade of 1940s. The variability of monsoon rainfall, expressed in terms of its coefficient of variation, has been relatively larger in the last 3 decades. The paper mainly discusses the large-scale behaviour of recent monsoons during 1982-88. In particular, the ENSO-monsoon-linkages vis-a-vis the recent ENSO episodes of 1982-83 and 1986-87 are emphasised.

Vuille, M., R. S. Bradley, et al. (2000). "Interannual climate variability in the Central Andes and its relation to tropical Pacific and Atlantic forcing." Journal of Geophysical Research, Washington, DC 105(D10): 12447-12460.

The main spatiotemporal modes of interannual temperature and austral summer (DJF) precipitation variability in the Central Andes are identified based on a two-way principal component analysis (PCA) of 30-year (1961-1990) monthly station data and related to contemporaneous tropical Pacific and Atlantic sea surface temperature anomalies (SSTAs). In addition, various meteorological fields, based on National Centers for Environmental Prediction /National Center for Atmospheric Research (NCEP/NCAR) reanalysis, NOAA-Outgoing Longwave Radiation (OLR) and station data, are analyzed during periods of strong positive and negative SSTA and the respective composites tested for local significance using a Student's t-test approach. Temperature variability in the Central Andes is primarily related to El Nino-Southern Oscillation (ENSO) and closely follows SSTA in the central equatorial Pacific with a lag of 1-2 months. In the southern Altiplano, temperatures have significantly increased since the late 1970s. DJF precipitation is also primarily related to ENSO, featuring below (above) average precipitation during El Nino (La Nina). Precipitation over the dry western part of the Altiplano shows the closest relationship with ENSO, due to ENSO-induced atmospheric circulation anomalies. Precipitation variability over the western Altiplano features a decadal-scale oscillation, related to a similar climatic shift in the tropical Pacific domain in the late 1970s. Over the northern Altiplano the precipitation signal is reversed in the austral summer following the peak phase of ENSO, presumably due to the temporal evolution of tropical Pacific SSTA, rapidly switching from one state to the other. No evidence for a tropical Atlantic influence on DJF precipitation was found. SSTAs in the tropical NE Atlantic, however, presumably are influenced by heating and convection over the Altiplano through an upper air monsoon return flow, altering the strength of the NE trades that emanate from the Sahara High.

Wajsowicz, R. C. and P. S. Schopf (2001). "Oceanic Influences on the Seasonal Cycle in Evaporation over the Indian Ocean." Journal of Climate 14(6): 1199-1226.

The annual mean and seasonal cycle in latent heating over the Indian Ocean are investigated using a simple, analytical ocean model and a 3D, numerical, ocean model coupled to a prescribed atmosphere, which permits interaction through sea surface temperature (SST). The role of oceanic divergence in determining the seasonal cycle in evaporation rate is reexamined from the viewpoint that the amount of rainfall over India during the southwest monsoon is a function of the amount of water evaporated over the "monsoon streamtube" as well as orographically induced convective activity. Analysis of Comprehensive Ocean-Atmosphere Dataset (COADS) shows that nearly 90% of the water vapor available to precipitate over India during the southwest monsoon results from the annual mean evaporation field. The seasonal change in direction of airflow, which opens up a pathway from the southern Indian Ocean to the Arabian Sea, rather than the change in evaporation rate is key to explaining the climatological cycle, though the change in latent heating due to seasonal variations is similar to that needed to account for observed interannual-to-interdecadal variability in monsoon rainfall. The simple model shows that net oceanic heat advection is not required to sustain vigorous evaporation over the southern tropical Indian Ocean; its importance lies in ensuring that the maximum evaporation occurs during boreal summer. Also shown with the simple model is that evaporation over the Arabian Sea cannot increase sufficiently to make up for the loss of water vapor accumulated over the southern Indian Ocean should there be a change in circulation such that the Southern Ocean is no longer part of the monsoon streamtube. Analytical, periodic solutions of the linearized heat balance equation for the simple model are presented under the assumption that the residual of net surface heat flux minus rate of change of heat content (DIV) is considered to be an external periodic forcing independent of SST to first order. These solutions, expressed as functions of the amplitude and phase of DIV, lie in two regimes. The first regime is characterized by increases (decreases) in the amplitude of DIV resulting in an increase (decrease) in the amplitude of the solution. In contrast, in the second regime, the amplitude of the solution decreases (increases) as the amplitude of DIV increases (decreases). It is noteworthy that the regime boundaries for SST and latent heating do not necessarily coincide. For the present climate, as determined from COADS, the southern Indian Ocean's annual harmonics of latent heating and SST lie in the second regime near the border, and so their tendencies are sensitive to the nature of the perturbation to the harmonic in DIV. The southern Indian Ocean's semiannual harmonic of latent heating lies in the first regime, and so its tendency is robust to the nature of the perturbation to the harmonic in DIV; that of SST lies in the second regime near the border. Contrasting runs of the 3D numerical model, in which the Indonesian throughflow differs by less than 4 x 10 super(6) m super(3) s super(-1) in the annual mean and less than plus or minus 2 x 10 super(6) m super(3) s super(-1) in seasonal variability, provides new estimates for its potential role in the Indian Ocean heat balance. Net surface heat flux differences of over 20 W m super(-2) are found along the length and breadth of the southwest monsoon streamtube: particularly noteworthy regions are over the Somali jet and to the east of Madagascar. These changes can be explained in part by the changes in oceanic meridional transport generated by the throughflow as well as by its heat input. Spatial resolution and upper ocean physics are sufficient for the throughflow to retain its zonal jet character across the Indian Ocean and so inhibit meridional overturning. Significantly, its presence reduces the amount of heat imported into the Southern Ocean from the Arabian Sea during boreal summer, so making SSTs in the Arabian Sea higher.

Wajsowicz, R. C. and P. S. Schopf (2001). "Oceanic influences on the seasonal cycle in evaporation over the Indian Ocean." Journal of Climate, Boston, MA 14(6): 1199-1226.

The annual mean and seasonal cycle in latent heating over the Indian Ocean are investigated using a simple, analytical ocean model and a 3D, numerical, ocean model coupled to a prescribed atmosphere, which permits interaction through sea surface temperature (SST). The role of oceanic divergence in determining the seasonal cycle in evaporation rate is reexamined from the viewpoint that the amount of rainfall over India during the southwest monsoon is a function of the amount of water evaporated over the ``monsoon streamtube'' as well as orographically induced convective activity. Analysis of Comprehensive Ocean-Atmosphere Dataset (COADS) shows that nearly 90% of the water vapor available to precipitate over India during the southwest monsoon results from the annual mean evaporation field. The seasonal change in direction of airflow, which opens up a pathway from the southern Indian Ocean to the Arabian Sea, rather than the change in evaporation rate is key to explaining the climatological cycle, though the change in latent heating due to seasonal variations is similar to that needed to account for observed interannual-to-interdecadal variability in monsoon rainfall. The simple model shows that net oceanic heat advection is not required to sustain vigorous evaporation over the southern tropical Indian Ocean; its importance lies in ensuring that the maximum evaporation occurs during boreal summer. Also shown with the simple model is that evaporation over the Arabian Sea cannot increase sufficiently to make up for the loss of water vapor accumulated over the southern Indian Ocean should there be a change in circulation such that the Southern Ocean is no longer part of the monsoon streamtube. Analytical, periodic solutions of the linearized heat balance equation for the simple model are presented under the assumption that the residual of net surface heat flux minus rate of change of heat content (DIV) is considered to be an external periodic forcing independent of SST to first order. These solutions, expressed as functions of the amplitude and phase of DIV, lie in two regimes. The first regime is characterized by increases (decreases) in the amplitude of DIV resulting in an increase (decrease) in the amplitude of the solution. In contrast, in the second regime, the amplitude of the solution decreases (increases) as the amplitude of DIV increases (decreases). It is noteworthy that the regime boundaries for SST and latent heating do not necessarily coincide. For the present climate, as determined from COADS, the southern Indian Ocean's annual harmonics of latent heating and SST lie in the second regime near the border, and so their tendencies are sensitive to the nature of the perturbation to the harmonic in DIV. The southern Indian Ocean's semiannual harmonic of latent heating lies in the first regime, and so its tendency is robust to the nature of the perturbation to the harmonic in DIV; that of SST lies in the second regime near the border. Contrasting runs of the 3D numerical model, in which the Indonesian throughflow differs by less than 4 x 10 super(6) m super(3) s super(-) super(1) in the annual mean and less than plus or minus 2 x 10 super(6) m super(3) s super(-) super(1) in seasonal variability, provides new estimates for its potential role in the Indian Ocean heat balance. Net surface heat flux differences of over 20 W m super(-) super(2) are found along the length and breadth of the southwest monsoon streamtube: particularly noteworthy regions are over the Somali jet and to the east of Madagascar. These changes can be explained in part by the changes in oceanic meridional transport generated by the throughflow as well as by its heat input. Spatial resolution and upper ocean physics are sufficient for the throughflow to retain its zonal jet character across the Indian Ocean and so inhibit meridional overturning. Significantly, its presence reduces the amount of heat imported into the Southern Ocean from the Arabian Sea during boreal summer, so making SSTs in the Arabian Sea higher.

Wake, C. P. and P. A. Mayewski (1993). "The spatial variation of Asian dust and marine aerosol contributions to glaciochemical signals in central Asia." Young, G. J.

Short-term (6 months to 17 years) glaciochemical records have been collected from several glacier basins in the mountains of central Asia. The spatial distribution of snow chemistry in central Asia is controlled by the influx of dust from the large expanse of arid and semi-arid regions in central Asia. Glaciers in the northern and western Tibetan Plateau show elevated concentrations and elevated annual fluxes of calcium, sodium, chloride, sulphate and nitrate due to the influx of desert dust from nearby arid and semi-arid regions. Glaciers in the southeastern Tibetan Plateau show lower concentrations and lower annual fluxes of major ions due to longer transport distances of dust from the arid and semi-arid regions of western China. Snow from the Karakoram and western Himalaya show ion concentrations similar to those in southeastern Tibetan Plateau, but much higher annual fluxes suggesting that much of the aerosol and moisture transported with the westerly jet stream is removed as it ascends the southwest margin of the Tibetan Plateau. Snow from the southern slopes of the eastern Himalayas shows very low concentrations and very low annual fluxes of major ions, indicating that this region is relatively free from the chemical influence of Asian dust. The glaciochemical data suggest that glaciers which are removed from large source areas of mineral aerosol, such as those in the Himalaya, the Karakoram, and the southeastern Tibetan Plateau, are the ones most likely to contain longer-term glaciochemical records which detail annual to decadal variation in the strength of the Asian monsoon and long-range transport of Asian dust.

Wang, B. (1995). "Interdecadal changes in El Nino onset in the last four decades." Journal of Climate, Boston, MA 8(2): 267-285.

The characteristics of the onset of the Pacific basin-wide warming have experienced notable changes since the late 1970s. The changes are caused by a concurrent change in the background state on which El Nino evolves. For the most significant warm episodes before the late 1970s (1957, 1965, and 1972), the atmospheric anomalies in the onset phase (November to December of the year preceding the El Nino) were characterized by a giant anomalous cyclone over east Australia whose eastward movement brought anomalous westerlies into the western equatorial Pacific, causing development of the basin-wide warming. Meanwhile, the trades in the southeastern Pacific (20 degrees S-0 degrees , 125 degrees -95 degrees W) relaxed back to their weakest stage, resulting in a South American coastal warming, which led the central Pacific warming by about three seasons. Conversely, in the warm episodes after the late 1970s (1982, 1986-87, and 1991), the onset phase was characterized by an anomalous cyclone over the Philippine Sea whose intensification established anomalous westerlies in the western equatorial Pacific. Concurrently, the trades were enhanced in the southeastern Pacific, so that the coastal warming off Ecuador occurred after the central Pacific warming. It is found that the atmospheric anomalies occurring in the onset phase are controlled by background SSTs that exhibit a significant secular variation. In the late 1970s, the tropical Pacific between 20 degrees S and 20 degrees N experienced an abrupt interdecadal warming, concurrent with a cooling in the extratropical North Pacific and South Pacific and a deepening of the Aleutian Low. The interdecadal change of the background state affected El Nino onset by altering the formation of the onset cyclone and equatorial westerly anomalies and through changing the trades in the southeast Pacific, which determine whether a South American coastal warming leads or follows the warming at the central equatorial Pacific.

Wang, B. and Z. Fang (2000). "Impacts of shortwave radiation forcing on ENSO: a study with a coupled tropical ocean-atmosphere model." Climate Dynamics, Berlin, Germany 16(9): 677-691.

We describe a coupled tropical ocean-atmosphere model that represents a new class of models that fill the gap between anomaly coupled models and fully coupled general circulation models. Both the atmosphere and ocean are described by two and half layer primitive equation models, which emphasize the physical processes in the oceanic mixed layer and atmospheric boundary layer. Ocean and atmosphere are coupled through both momentum and heat flux exchanges without explicit flux correction. The coupled model, driven by solar radiation, reproduces a realistic annual cycle and El Nino-Southern Oscillation (ENSO). In the presence of annual mean shortwave radiation forcing, the model exhibits an intrinsic mode of ENSO. The oscillation period depends on the mean forcing that determines the coupled mean state. A perpetual April (October) mean forcing prolongs (shortens) the oscillation period through weakening (enhancing) the mean upwelling and mean vertical temperature gradients. The annual cycle of the solar forcing is shown to have fundamental impacts on the behavior of ENSO cycles through establishing a coupled annual cycle that interacts with the ENSO mode. Due to the annual cycle solar forcing, the single spectral peak of the intrinsic ENSO mode becomes a double peak with a quasi-biennial and a low-frequency (4-5 years) component; the evolution of ENSO becomes phase-locked to the annual cycle; and the amplitude and frequency of ENSO become variable on an interdecadal time scale due to interactions of the mean state and the two ENSO components. The western Pacific monsoon (the annual shortwave radiation forcing in the western Pacific) is primarily responsible for the generation of the two ENSO components. The annual march of the eastern Pacific ITCZ tends to lock ENSO phases to the annual cycle. The model's deficiencies, limitations, and future work are also discussed.

Wang, B. and T. Li (1993). "A simple tropical atmosphere model of relevance to short-term climate variations." Journal of the Atmospheric Sciences, Boston, MA 50(2): 260-284.

The tropical atmosphere model presented here is suitable for modeling both the annual cycle and short-term (monthly to decadal time scale) climate fluctuations in sole response to the thermal forcing from the underlying surface, especially the ocean surface. The present model consists of a well-mixed planetary boundary layer and a free troposphere represented by the gravest baroclinic mode. The model dynamics involves active interactions between the boundary-layer flow driven by the momentum forcing associated with sea surface temperature (SST) gradient and the free tropospheric flow stimulated by diabatic heating that is controlled by the thermal effects of SST. This process is demonstrated to be essential for modeling Pacific basinwide low-level circulations. The convective heating is parameterized by a SST-dependent conditional heating scheme based upon the proposition that the potential convective instability increases with SST in a nonlinear fashion. The present model integrates the virtue of a Gill-type model with that of a Lindzen-Nigam model and is capable of reproducing both the shallow intertropical convergence zone (ITCZ) in the boundary layer and the deep South Pacific convergence zone (SPCZ) and monsoon troughs in the lower troposphere. The precipitation pattern and intensity, the trade winds and associated subtropical highs, and the near-equatorial trough can also be simulated reasonably well. The thermal contrast between oceans and continents is shown to have a profound influence on the circulation near landmasses. Changes in land surface temperature, however, do not exert significant influence on remote oceanic regions. Both the ITCZ and SPCZ primarily originate from the inhomogeneity of ocean surface thermal conditions. The continents of South and North America contribute to the formation of these oceanic convergence zones through indirect boundary effects that support coastal upwelling changing the SST distribution. The diagnosis of observed surface wind and pressure fields indicates that the nonlinear advection of momentum is generally negligible, even near the equator, in the boundary-layer momentum balance. The large SST gradients in the subtropics play an important role in forcing rotational and cross-isobaric winds.

Weng, H. and K. M. Lau (1996). "Low-frequency time-space regimes in tropical convection." Theoretical and Applied Climatology, Vienna, Austria 55(1-4): 89-98.

The multi-scale time-space regimes of the low-frequency convective activity over the maritime continent and tropical western Pacific are investigated using the monthly infrared radiance black body temperature (IRTBB) over a latitude band of 5S-9S, 80E-160W for the time period of 1980-1993. The complex Morlet wavelet transform and the complex empirical orthogonal function (CEOF) analysis are used. The zonal mean of the monthly IRTBB is dominated by the annual cycle which is influenced by a monsoon regime. An interannual signal around the time scale of 4.8-year and a decadal signal are obvious. In the zonal deviation, each CEOF represents a particular spatial regime; its corresponding principal component exhibits different multi-scale temporal behavior. The first leading component represents the variability due to large scale land-ocean distribution (the maritime continent, the Indian Ocean and the western Pacific) related to monsoon, with a dominant annual time scale. The second leading component represents the fluctuation of Walker circulation, associated with the El Nino-Southern Oscillation (ENSO) events having a main time scale around 4.8-year and the quasi-biennial oscillation (QBO) around 2.4-year. The third leading component represents the variability due to small-scale land-ocean distribution (Java, New Guinea and the surrounding seas), with a dominant annual time scale. The main time scales in all the components seem to be modulated by longer time scales in either amplitude or frequency or both. Different time scales, as well as their in-phase interference, may play different roles in developing an individual ENSO event. The 1982/1983 event is dominated by an enhanced QBO. The 1986/1987 event is dominated by an enhanced 4.8-year oscillation. The 1991 and 1993 events may have resulted from an in-phase interference among several interannual time scales, abnormal annual cycles, and also high-frequency variability.

Wu, A. and D. Hu (2000). "Equatorial Pacific SSTA-related decadal variations of potential predictability of ENSO and interannual climate." Meteorology and Atmospheric Physics, Vienna, Austria 74(1-4): 1-9.

Based on analysis of NCEP reanalysis data and SST indices of the recent 50 years, decadal changes of the potential predictability of ENSO and interannual climate anomalies were investigated. Autocorrelation of Nino3 SST anomalies (SSTA) and correlation between atmospheric anomalies fields and Nino3 SSTA exhibit obvious variation in different decades, which indicates that Nino3 SSTA-related potential predictability of ENSO and interannual climate anomalies has significant decadal changes. Time around 1977 is not only a shift point of climate on the interdecadal time scale but also a catastrophe point of potential predictability of ENSO and interannual climate. As a whole, ENSO and the PNA pattern in boreal winter are more predictable in 1980s than in 1960s and 1970s, while the Nino3 SSTA-related potential predictability of the Indian monsoon and the East Asian Monsoon is lower in 1980s than in 1960s and 1970s.

Xie, Z. and Y. Luo (1999). "The effects of snow cover of Tibet Plateau on climate over China." Quarterly Journal of Applied Meteorology, Beijing, China 10: 122-131.

The snow cover of Tibet Plateau is an important factor which affects the climate over China. In addition to the obvious seasonal change, the interannual and interdecadal changes of the snow cover are obvious, too. The snow cover could affect the progress of monsoon, general circulation in East Asia, and temperature, precipitation of China in terms of changing the thermodynamical effects of Tibet Plateau. The persistence of the snow cover is long, and it has the property of big amplitude change, and scientists pay more attention to its climatic effects and its position as a seasonal and interannual forecasting factor.

Xu, J. and Q. Zhu (1998). "East-Asian monsoon QBO and its relation to ENSO variability." Journal of Nanjing Institute of Meteorology, Nanjing, China 21(1): 23-31.

In the context of wavelet technique and coherence analysis the existence of east Asian monsoon QBO is investigated together with its relation to ENSO variability. Results suggest that the monsoon exhibits noticeable QBO but the periods and amplitudes show significant change on an interdecadal basis with the QBO evolution in close relation to an El Nino episode. The western Pacific warm pool serves as a key area connecting the monsoon and ENSO cycle in such a way that the strong QBO winter monsoon first gives rise to a teleconnection wavetrain, followed by an anomaly occuring in the warm pool that is then moving eastward, exerting an effect on equatorial eastern Pacific SST, causing El Nino happening. The monsoon QBO is responsible for strong seasonal ENSO phase-locking and for its warm phase lasting one year or so.

Xu, J., Q. Zhu, et al. (1998). "Interrelation between East-Asian winter monsoon and Indian/Pacific SST with the interdecadal variation." Acta Meteorologica Sinica, Beijing, China 12(3): 275-287.

Investigated statistically is the interrelation between East Asian winter monsoon (EAWM) and SST over sensitive areas of the Indian and Pacific Oceans, with focus on the relation of EAWM to strong ENSO signal area, i.e., the equatorial eastern Pacific (EEP) SST. Evidence suggests that the EAWM variation is intimately associated not only with the EEP SST but with the equatorial western Pacific ``warm pool'' and equatorial Indian/northwestern Pacific Kuroshio SST as well; the EAWM and ENSO interact strongly with each other on the interannual time scales, exhibiting pronounced interdecadal variation mainly under the joint effect of the monsoon QBO and the monsoon/SST background field features on an interdecadal basis--when both fields are in the same phase (anti-phase), strong EAWM contributes to EEP SST rise (drop) in the following winter, corresponding to a warm (cold) ENSO cycle; the EAWM QBO causes ENSO cycle to be strong phase-locked with seasonal variation, making the EEP SST rise lasting from April-May to May-June of the next year, which plays an important role in maintaining a warm ENSO phase.

Xu, J., Q. Zhu, et al. (1999). "Sudden and periodic changes of East Asian winter monsoon in the past century." Quarterly Journal of Applied Meteorology, Beijing, China 10(1): 1-8.

Based on mean sea level pressure (MSLP) data, the East Asian winter monsoon intensity indexes were calculated from 1873 to 1990. The sudden and periodic changes of East Asian winter monsoon were studied by the method of sliding t-test and singular spectral analysis (SSA). The results show that East Asian winter monsoon intensity displays obvious interannual and interdecadal variations. When winter monsoon increases, the temperature in most regions of China decreases. Mongolian high raises and Aleutian low deepens, and reverse in weak winter monsoon year. Meanwhile, East Asian winter monsoon shows quasi-biennial oscillation (QBO), low frequency oscillation (3 similar to 7 years) and interdecadal oscillation (more than 10 years). These three periodic oscillations appear to have strong interdecadal variability.

Xu, J. j., Q. Zhu, et al. (1997). "East Asian winter monsoonAENSO cycle relation with interdecadal anomaly in the past 100 years." Chinese Journal of Atmospheric Sciences, New York, NY 21(4): 325-331.

This paper is devoted to the study of interrelation between the East Asian winter monsoon (EAWM) and ENSO cycle alongside the interdecadal anomaly in the past 100 years by correlation and sliding correlation techniques. It turns out that the interannual relationship between EAWM and the eastern equatorial Pacific SST is characterized by interdecadal variability; the EAWM-ENSO relation is under the joint effects of the monsoon QBO and monsoon-SST background fields on an interdecadal basis. When these two fields are in the same (opposite) state, intense EAWM contributes to the SST rise (drop) in the following winter, leading to an El Nino (La Nina) event.

Yamagata, T. and Y. Masumoto (1992). "Interdecadal natural climate variability in the western Pacific and its implication in global warming." Journal of the Meteorological Society of Japan, Tokyo, Japan 70(1B): 167-175.

Long-term hydrographic observations repeated by the Japan Meteorological Agency in the western Pacific have revealed not only the oceanic thermal variability associated with the ENSO events but also another interdecadal variability seemingly related to the global warming trend from the late 1970s. Since the background SST is high in the tropical western Pacific, even weak SST anomalies may affect strongly the atmospheric circulation including the Aleutian Low and the Asian winter monsoon. The extratropical atmospheric response to the interdecadal SST anomaly is global and looks quite different from that for the ENSO time scale. We note that the response is even reversed in the Asian monsoon region. To the west of the date line the ocean behaves like a dynamical slave to the winter Asian monsoon as demonstrated using the ocean general circulation model. In particular, the winter monsoon and related easterly wind variations are responsible for maturity or immaturity of the cold Mindanao Dome off the Phillipine coast. However, the active (inactive) summer monsoon followed by the anomalous easterlies (westerlies) intensified over the tropical western Pacific from summer through winter appears to be responsible for the positive (negative) SST anomalies in the same area at least for the ENSO time scale. This suggests that an interesting positive feedback mechanism responsible for natural climate variabilities ranging from several years to decades may exist in the coupled ocean-atmosphere-land system in the western tropical Pacific.

Yarnal, B. (1992). "Short-term climatic variability." Majumdar, Shyamal K., et al.

Global-scale climatic variations are never uniform over the Earth's surface, and the specific impacts of global warming on each region's biophysical and social systems will depend on how each region's climate responds to the global temperature rise. The main ways in which present-day climate varies are intorduced, providing a foundation on which to base an understanding of future climatic variation; attention is given to within-year, year-to-year, and decade-to-decade climatic variations. Within-year variations are considered with regard to persistent climatic regimes, with emphasis given to blocking in the extratropical westerlies, which are characterized by regional climatic anomalies. Also considered is the so-called 40-50 day oscillation in the tropics, which affects the onset, breaks and withdrawal of the monsoon systems of Asia. Regarding year-to-year variations, it is noted that the phase of the 2.2-year Quasi-Biennial Oscillation (QBO) is a controlling factor of the number of tropical storms and hurricanes occurring in the tropical Atlantic. Attention is also given to teleconnections, which are global-scale climatic phenomena with regional impacts, and which are products of the interaction between the dynamic atmosphere and global geography. These include the Southern Oscillation, which involves the inverse relationship of surface pressure over the maritime continent of the southwest Pacific, and which relates to the ENSO phenomenon, linked to extratropical climatic anomalies. Other teleconnections are the Pacific/North American pattern, whose phase pattern correlates strongly with temperature and precipitation fields over North America, as well as with El Nino winters; and the North Atlantic Oscillation, a north-south dipole, one phase of which represents coincident intensification of the Azores high and the Icelandic low. Concerning decade-to-decade climatic variations, scientists have recognized a significant statistical correlation between climate variables and either the 11-year sunspot cycle or the 22-year double-sunspot cycle, and recently have uncovered strong, ubiquitous, and consistent empirical evidence for the sunspot-climate connection, which suggests that the solar cycle affects regional climates differently during each phase of the QBO. It is also noted that on decadal time scales, precipitation is more sensitive than temperature to atmosphere-circulation variations.

Yasuda, T. and K. Hanawa (1999). "Composite analysis of North Pacific subtropical mode water properties with respect to the strength of the wintertime East Asian monsoon." Journal of Oceanography, Tokyo, Japan 55(4): 531-541.

The interannual variation of the thermal structure of North Pacific subtropical mode water (NPSTMW) is investigated by means of composite analysis with respect to the wintertime Monsoon Index (MOI) which can represent the strength of the wintertime East Asian monsoon. The wind stress field over the NPSTMW formation area has significant variation over the interannual (2-4 year) and the decadal (10-20 year) bands. Changes in interannual variation are well correlated with the intensity of the wintertime East Asian monsoon. By means of composite analysis, it is found that significant differences occur in the thermal structure of the NPSTMW between stronger and weaker monsoon years. That is, colder and thicker NPSTMW is formed in years with stronger monsoons. Analysis of the heat flux through the sea surface and horizontal heat divergence in the Ekman layer shows that colder and thicker NPSTMW in stronger monsoon years can be attributed to a larger amount of heat release through the sea surface in the formation area. A larger horizontal divergence of the heat transport in the upper Ekman layer is considerably responsible for this increased heat loss.

Zhang, J. and T. J. Crowley (1989). "Historical climate records in China and reconstruction of past climates." Journal of Climate, Boston 2(8): 833-849.

The principal results of studies on historical climate change from A.D. 1000 to the present in China are reviewed. The studies are based on analysis of local annals and court records. After discussing the methodology of transferring descriptive accounts into quantitative estimates of past climates, we summarize the main results, which are generally substantiated by multiple lines of evidence: 1) There were significant historical climate fluctuations in China, with a range of about 1.0 degrees -1.5 degrees C in recent centuries. 2) Significant decadal-scale warm fluctuations occurred during a cool interval broadly correlative with the Little Ice Age. 3) There was an increased frequency of both droughts and floods in some parts of China during the Little Ice Age. Increased frequencies of dust storms accompanied the dry phases of the cool periods. 4) The spatial pattern of some Little Ice Age precipitation changes appears to reflect a modified development of different phases of the summer monsoon. 5) As suggested by recent GCM studies, enhanced Little Ice Age aridity may be due to increased winter snow cover causing temperature and soil moisture feedbacks the following spring. 6) Although there is some agreement between climate change in China and elsewhere, there are also indications that significant lags occur between the timing and direction of climate change in different regions. This pattern appears different from the warming trend of the past century, which is more uniform in both hemispheres.

Zhou, J. and K. M. Lau (2001). "Principal modes of interannual and decadal variability of summer rainfall over South America." International Journal of Climatology 21(13): 1623-1644.

Using the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) product together with the Goddard Earth Observing System (GEOS) reanalysis and the National Center for Environmental Prediction (NCEP) sea-surface temperature (SST) data, we have conducted a diagnostic study of the interannual and decadal scale variability of principal modes of summer rainfall over South America for the period 1979-1995. By filtering the annual and short (< 12 months) time-scale variations, results of empirical orthogonal function analysis show three leading modes of rainfall variation identified with interannual, decadal and long-term variability. Together, these modes explain more than half the total variance of the filtered data. The first mode is highly correlated with El Nino-Southern Oscillation (ENSO), showing a regional rainfall anomaly pattern largely consistent with previous results. This mode captures the summer season interannual variability, not only the Northeast Brazil drought but also its connection with excessive rainfall over Southern Brazil and the Ecuador coast in El Nino years. Another distinctive feature is the strengthening of the low-level flow along the eastern foothills of the eastern Andes, signifying an enhancement of the South American summer monsoon in response to an El Nino anomaly. The decadal variation displays a meridional shift of the Inter-Tropical Convergence Zone (ITCZ), which is tied to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. Associated with this mode is a large-scale mass swing between polar regions and the mid-latitudes. Over the South Atlantic and the South Pacific, the anomalous subtropical high and the associated anomalous surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of atmospheric forcing at the decadal time scale. The long-term variation shows that since 1980 there has been a decrease of rainfall from the northwest coast to the southeast subtropical region and a southwards shift of the Atlantic ITCZ, leading to increased rainfall over northern and eastern Brazil. Possible links of this mode to the observed SST warming trend over the subtropical South Atlantic and to the interdecadal SST variation over the extratropical North Atlantic are discussed.

Zhu, Q. and J. Xu (1998). "Observational study on the effect of ENSO and its interdecadal variations on the climate anomaly in eastern China." Journal of Nanjing Institute of Meteorology, Nanjing, China 21(4): 615-623.

The relationship between the east Asian monsoon (EAM) and ENSO events is different on the different interdecadal background in SST fields. The largest anomaly center of precipitation locates in the south side of the Changjiang river in the next summer of ENSO events on the cold SST interdecadal background, with its counterpart in the Huanan area in the next spring on the warm background. The temperature variation is not corresponding to the rainfall. The interdecadal background of SST affects the air-sea heat flux exchange and the thermal contrast between land and ocean, thus changing the monsoon intensity and the relation of ENSO and EAM.

Zhu, Y., W. Qian, et al. (1999). "Tropical sea surface temperature anomaly and Indian summer monsoon." Acta Meteorologica Sinica, Beijing, China 13(2): 154-163.

The time series of the sea surface temperature (SST) anomaly, covering the eastern (western) equatorial Pacific, central Indian Ocean, Arabian Sea, Bay of Bengal and South China Sea (SCS), have been analyzed by using wavelet transform. Results show that there exists same interdecadal variability of SST in the tropical Pacific and tropical Indian Ocean, and also show that the last decadal abrupt change occurred in the 1970s. On the interannual time scale, there is a similar interannual variability among the equatorial central Indian Ocean and the adjacent three sea basins (Arabian Sea, Bay of Bengal and South China Sea), but the SST interannual changes of the Indian Ocean lagged 4-5 months behind that of the equatorial central-east Pacific. Meanwhile, the interannual variability and long-range change between SST anomaly and Indian summer monsoon rainfall in recent decades have been explained and analyzed. It indicates that there existed a wet (dry) period in India when the tropical SST was lower (higher) than normal, but there was a lag of phase between them.

Zveryaev, II (2002). "Interdecadal changes in the zonal wind and the intensity of intraseasonal oscillations during boreal summer Asian monsoon." Tellus. Series A: Dynamic Meteorology and Oceanography 54A(3): 288-298.

Decadal-interdecadal changes in the intensity of intraseasonal oscillations (ISO) and in the summer mean wind fields in the Asian monsoon system are investigated using 51 yr of 850 hPa zonal wind data obtained from the National Centers for Environmental Prediction - National Center for Atmospheric Research (NCEP/NCAR) Reanalysis. Decadal-interdecadal variations contribute significantly to the total variability of the summer mean 850 hPa zonal wind (30-45%) and the ISOs intensity (20-35%). These variations in the summer mean 850 hPa zonal wind and in the intensity of the 30-60 d ISO have a distinct zonal structure and are associated with the strength of low level westerlies and with meridional dynamics of the Tropical Convergence Zone (TCZ). Interdecadal changes in the intensity of the 10-20 d ISO are most pronounced over the eastern Indian Ocean, the South China Sea and the western tropical Pacific. Singular value decomposition (SVD) analysis revealed a strong correlation on an interdecadal timescale between the sea surface temperatures (SST) in the Indian Ocean and the summer mean 850 hPa zonal wind and the intensity of the ISOs in the Asian summer monsoon, whereas such correlations on a decadal timescale are weak. The temporal expansion coefficients of the first SVD mode show a climate regime shift in the mid-late 1970s. During the last few decades, SST in the Indian Ocean increased, resulting in a decreased land-sea heat contrast and weaker low-level westerlies over northern Indian Ocean, the Indian subcontinent, and Indochina. In response to sea surface warming and associated enhanced convection, the 30-60 d ISO became stronger over the equatorial central and western Indian Ocean and the South China Sea, and weaker over the Indian subcontinent, the northern Arabian Sea and the Bay of Bengal. Meanwhile a 10-20 d ISO intensified over the eastern Indian Ocean, the South China Sea, and the western tropical Pacific.