References for “The Asian Monsoon” book – Chapter 4

Abbott, D. A. (1977). "Hemispheric simulation of the Asian summer monsoon." Pure and Applied Geophysics, Basel 115(5/6): 1111-1130.

A three-level, beta -plane, filtered model is used to simulate the Northern Hemisphere summer monsoon. A time-averaged initial state, devoid of subplanetary scale waves, is integrated through 30 days on a 5 degrees -lat.-long. grid. Day 25-day 30 integrations are then repeated on a 2.5 degrees grid. The planetary-scale waves are forced by time-independent, spatially varying, diabatic heating. Energy is extracted via internal and surface frictional processes. Orography is excluded to simplify synoptic-scale energy sources. During integration, the model energy first increases, but stabilizes near day 10. Subsequent flow patterns resemble the hemisphere summer monsoon. Climatological features remain quasi-stationary. At 200 mb, high pressure dominates the land area, large-scale troughs are found over the Atlantic and Pacific oceans, the easterly jet forms south of Asia, and subtropical jets develop in the westerlies. At 800 mb, subtropical highs dominate the oceans, and the monsoon trough develops over the Asian land mass. The planetary scales at all levels develop a realistic cellular structure from the passage of transient synoptic-scale features; e.g., a baroclinic cyclone track develops near 55 degrees N and westward propagating waves form in the easterlies. Barotropic redistribution of kinetic energy is examined over a low-latitude zonal strip by using a Fourier wave space. In contrast to higher latitudes in which the zonal flow and both longer and shorter waves are fed by barotropic energy redistribution from the baroclinically unstable wavelengths, the low-latitude waves have a planetary-scale kinetic energy source. Wavenumbers 1 and 2 maintain both the zonal flow and all shorter scales via barotropic transfers. Transient and standing wave processes are examined individually and in combination. Wave energy accumulates at wave numbers 7 and 8 at 200 mb and at wave number 11 in the lower troposphere. The 800-mb waves are thermally indirect and, in the mean, they give energy to the zonal flow. These characteristics agree with atmospheric observation. The energy source for these waves is the three wave barotropic transfer. The implications of examining barotropic processes in a Fourier wave space vs. the more common approach of separating the flow into a mean plus a deviation, are discussed.

Abdulkarim Ahmed, S. (1983). "Jet streams at 150 mb during a large-scale drought in Indian summer monsoon." Mausam, New Delhi 34(1): 55-60.

During 1972, a year of large-scale drought in the Indian summer monsoon rainfall, the mean u-field at 150 mb shows a weaker than normal tropical easterly jet stream over south Asia and a stronger than normal subtropical westerly jet stream over Australia; the mean v-field shows that the cross-equatorial northerlies are weaker and displaced eastward by similar to 20 degrees long. The two years (1970 and 1975) of highest monsoon rainfall for India of the decade 1970-1979 were compared with the two years (1972 and 1979) of lowest monsoon rainfall in the strength of the subtropical jet stream (STJ) over Australia as seen from an analysis of monthly mean u-fields of July and Aug. It is seen that, during the poor rainfall years, the STJ is similar to 20% stronger than in the good monsoon years.

Ackerman, S. A. and S. K. Cox (1989). "Surface weather observations of atmospheric dust over the southwest summer monsoon region." Meteorology and Atmospheric Physics, Vienna 41(1): 19-34.

Surface weather observations are analyzed to investigate the temporal and spatial distributions of dust loading associated with the southwest summer monsoon region in India. The 1979 annual distribution of dust days for the region 10-37 degrees N and 35-90 degrees E are presented. Five-year composites of dust loading for the months May, June, and July are derived. Results are analyzed with regard to preferred wind direction and wind speed associated with dust loading, potential source regions, and regions of deposition. A case study of the meteorological conditions of a dust outbreak that occurred over the Arabian Peninsula in June of 1979 is given. Rawinsonde temperature observations are analyzed to locate the top of the dust layer over the Rub al Khali Desert. The top of the dust layer was found to vary from 400 mb during the summer to 600 mb in the late spring and early fall.

Alekseyeva, L. I., V. V. Vinogradova, et al. (1988). "Spatial-temporal structure of wave disturbances over the Indian Ocean basin during the period of the southwestern monsoon." Moscow. Universitet, Vestnik, Ser. Geografiya, Sept./Oct(5): 40-43.

The spatial and temporal structure and the predominant modes of variability of the wind field in the lower troposphere were investigated by spectral analysis of the zonal and meridional component of the wind vector during two monsoon seasons of contrasting activity: 1982 (a drought year) and 1983 (a year with abundant rainfall). An analysis of the distribution of the function of spectral density of the zonal and meridional components showed that, over the region investigated in the Indian Ocean (30 degrees N lat.-30 degrees S lat.; and 30-100 degrees E long.), there are two types of wave disturbances, with periods of 2-3 weeks and 3-10 days. In the latter range, there are two spectral maxima: one with a period of 6-10 days and the other, 3-5 days. In the classification of Monin, fluctuations with a period of 14-21 days may be ascribed to a global scale and fluctuations with a period of 3-10 days to a synoptic scale. The distribution of the dispersion of zonal and meridional wind components at the 850-hPa surface with periods of 2-3 weeks and 3-5 and 6-10 days is described with maps. The authors demonstrate the coincidence of regions of maximum activity of processes of different periodicity of the global scale with a periodicity of 2-3 weeks and of synoptic scale with a periodicity of 3-5 and 6-10 days. A single-type distribution of dispersion in years with different monsoon activity as a whole indicates that the detected fluctuations and regions of their localization are characteristic of the Indian monsoon.

Ananthakrishnan, R. and R. N. Kesavamurthy (1974). "Some new features of the vertical distribution of temperature and humidity over Bombay during the southwest monsoon season." Journal of the Marine Biological Association of India, Ernakulam 14(2): 732-742.

The aerological data of Bombay with the new American type of radiosonde were examined for the monsoon seasons of 1968, 1969, and 1970. Even during the peak monsoon months of July and Aug., large changes occur in the thermal and humidity structure of the atmosphere. It is found that, except during spells of good rainfall over and around the station, the depth of moist air over Bombay rarely exceeds 750 mb, above which there is often an inversion or layer of stable lapse rate with dry air aloft. On some occasions, there is again an increase of humidity towards the 500-mb level, and an inversion or layer of stable lapse rate is also noticed near this level. These features are illustrated with tephigrams for the months of July and Aug. 1968. Examination of upper wind flow patterns shows that the meridional component of the winds at and above 3 km tends to be northerly when the atmosphere is dry with little or no rainfall, while it is southerly when the humidity content is high. The continental origin of the air as well as subsidence appear to be responsible for the low humidity and inversion. The study shows that it is not correct to assume that a deep moist column of air exists over peninsular India after the monsoon has begun. Large space-time variations occur in the vertical distribution of humidity. Vertical transport of moisture beyond the first 2 or 3 km is brought out only by low-level convergence associated with weather systems of various scales, and there are compensating areas of descending motion outside the rainfall area.

Anderson, B. T., J. O. Roads, et al. (2000). "Large-scale forcing of summertime monsoon surges over the Gulf of California and the southwestern United States." Journal of Geophysical Research, Washington, DC 105(D19): 24455-24467.

Synoptic forcing of the Gulf of California summertime low-level wind field is described using a nested regional modeling system. Under appropriate synoptic conditions, strong surge events develop that are characterized by persistent, vertically extensive (1-2 km) southerly flow extending along the entire Gulf of California and into Arizona, California, and even southern Nevada. These surge periods are initiated either by tropical-cyclone activity to the south of Baja California or by the westward propagation of lower tropospheric troughs from over the Sierra Madre Occidental to the eastern Pacific. The flow over the Gulf is primarily geostrophic and is associated with the presence of these low-pressure centers to the south and west of Baja California.

Annamalai, H. and J. Slingo (1998). "The Asian summer monsoon, 1997." Weather, Bracknell, England 53(9): 284-287.

The rainfall associated with the Asian summer monsoon provides the main source of fresh water to millions of people in India, south China and the adjoining regions. Agriculture is the backbone of the economy of these countries. A delay in the onset of the monsoon and uneven spatial and temporal variability within the season may result in deficits in the seasonal mean all-India rainfall (AIR) which can have profound social and economical consequences (Pant and Rupa Kumar 1997). During the northern spring of 1997, the tropics experienced the unusually rapid development of a strong El Nino (Slingo, this issue). With the conditions prevailing in 1997, many dynamical models predicted a weaker than normal monsoon rainfall over India (e.g. Harrison et al. 1997). Similarly, the IMD predicted that the AIR would be 8 per cent below normal, less than one standard deviation and therefore not a significant deficit. In fact the seasonal mean monsoon precipitation over India was 2 per cent above normal (IMD 1997). Thus, seen in this context, the response of the Indian monsoon to the El Nino event of 1997 is a notable exception. This article examines the spatial distribution of precipitation on seasonal and subseasonal bases, and relates global weather patterns to the delayed onset of the monsoon season and the epochs of excessive and deficient rainfall within it. The authors conclude the rainfall distribution over India was highly variable in 1997, resulting in floods in some areas (e.g. Kerala) and drought in some other areas (e.g. Andhra Pradesh). The undue delay and persistent anticyclonic circulation over the eastern Indian Ocean suppressed the convection over the southern Indian states which recorded deficient rainfall (>20 per cent below normal). Heavy to very heavy rains in September over these regions damaged the standing crops. Both factors are likely to result in an overall drop of 5 per cent in the total crop production for India in 1997.

Appa Rao, G. (1981). "Atmospheric energetics over India during drought and normal monsoons." Mausam, New Delhi 32(1): 67-78.

Energetics of the atmosphere during a drought and normal southwest monsoons over India based upon upper air data were computed. The parameters considered are sensible heat, latent heat, kinetic energy, and angular momentum. The mean and eddy components caused by meridional circulation are separated, and the differences between the two contrasting years are highlighted. These results are compared with earlier ones obtained over India.

Appa Rao, G. (1985). "Moisture flux and vergence of water vapour over India during drought and good monsoons." Mausam, New Delhi 36(1): 97-100.

The water vapor flux and the vergence of moisture during drought and good monsoon seasons over India have been computed. The net moisture vergence over the country has been obtained. The diurnal variations in the fluxes and vergence based on 0000- and 1200-hr GMT observations have been evaluated. The contrasting features between the two years are discussed.

Appa Rao, G. and V. K. Pisal (1984). "Wave disturbance over Indian Ocean area during drought and normal summer monsoons." Mausam, New Delhi 35(3): 301-308.

The tropospheric wave disturbances over the Indian Ocean area during two contrasting summer monsoon periods are analyzed. The study reveals two significant waves with periodicity of 2-3 and 4-6 days in the meridional wind component. These waves move westward with a wavelength of similar to 20 and 32 degrees . respectively. The wave activity, in general, is stronger during the normal monsoon year than during the drought year.

Astling, E. G. (1978). "Study of 200-mb anticyclonic circulation centres over the Indian Ocean region." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 29(1).

Synoptic and dynamic aspects of anticyclonic circulation centers at 200 mb over the Indian Ocean region were investigated for the summer of 1972, when the monsoon circulation was delayed and weaker than normal. This study was based upon daily wind field analyses of data obtained from conventional rawinsonde and aircraft observations. Vorticity and divergence values around the upper tropospheric anticyclones were computed in areas where the number of data were dense. Comparisons of computational results were made with the distribution of convective clouds obtained from satellite brightness maps. Case studies for selected days and composite averages were prepared for circulation centers of various synoptic-scale sizes. The origin of unstable waves in the upper tropospheric easterlies, along the equatorward side of the Tibetan anticyclone, was investigated.

Astling, E. G. and C. R. Marsumoto (1978). "Study of 200-mb wind fields over the Indian Ocean region for the summer of 1972." Archiv fuer Meteorologie, Geophysik und Bioklimatologie, Ser A, Vienna 27(2): 117-127.

Synoptic and dynamic aspects of the 200-mb wind field over the Indian Ocean region were investigated for the summer of 1972 when the monsoon circulation was delayed and much weaker than normal. The study was based upon daily analyses of wind data obtained from conventional rawinsonde and aircraft observations. Vorticity and divergence values around the upper tropospheric anticyclones were computed in areas where the number of data were sufficiently dense. Comparisons of computational results were made with the distribution of convective clouds obtained from satellite brightness maps. Case studies for selected days as well as composite averages were prepared for circulation centers of various synoptic-scale sizes. Also, the origin of unstable waves in the upper tropospheric easterlies along the equatorward side of the Tibetan anticyclone was investigated.

Bagla, P. (2002). "Climate Forecasting: Drought Exposes Cracks in India's Monsoon Model." Science (Washington) 297(5585): 1265-1267.

The annual summer monsoon rains are vital to India's economy. But a drought this summer suggests that a homegrown prediction model might be all wet. India's first serious drought in 15 years is doing more than parching the soil and threatening the country's food supply. It has also stirred up a debate over the robustness of a homegrown climate forecasting model that badly missed predicting this summer's sharp decline in life-sustaining rains over much of the country. The summertime monsoon across India is among the toughest climatic phenomena to understand and predict because of the complex atmospheric conditions in the tropics.

Banerji, R. C. and D. S. Upadhayay (1982). "Severe drought of 1968-69 over Rajasthan." India. Geological Survey, Calcutta, Miscellaneous Publication(49): 161-172.

Rajasthan, the driest zone of India with a high degree of variability, is very sensitive to droughts. The last severe drought occurred during the year 1968-1969, when the rainfall was deficient during all the seasons. The monsoon withdrew 15 days earlier from northwest India in 1968 and Rajasthan remained dry the whole of Sept. A cold wave followed, and frost conditions in Nov.-Dec., 1968 completely destroyed the remaining crops. A synoptic study of this situation and a statistical analysis of the rainfall data during 1968-1969 are presented.

Bannister, A. J. and K. J. Smith (1993). "The South Pacific and southeast Indian Ocean tropical cyclone season 1990-91." Australian Meteorological Magazine, Canberra, Australia 42(4): 175-182.

During the 1990-91 season a total of eleven tropical cyclones affected the South Pacific and southeast Indian Ocean basins, of which five reached hurricane intensity (ten-minute mean wind speed in excess of 120 km h super(-) super(1) ). There was a total of 64 cyclones days spanning the period late November to mid-May, including 16 hurricane days. Sina and Joy caused damage costing US$55 million, accounting for over 95 per cent of the total cyclone damage in the basin. Eight lives were lost; six of these were associated with Joy and two with Fifi. Key features of the broadscale circulation included: a more active than normal westerly monsoon in the Australian region; a weaker than normal South Pacific convergence zone (SPCZ) and an anomalously weak long wave trough over eastern Asia (with fewer cross-equatorial surges over western Indonesia and the Indian Ocean). The Madden-Julian oscillations (MJO) were weaker and less regularly defined than in the preceding two seasons. The Southern Oscillation Index (SOI) was generally negative but small. Sea-surface temperatures (SST) remained above average in the equatorial central Pacific and warm SST anomalies, although generally small, persisted in the tropical Indian Ocean.

Bao, C.-l. (1982). "Aspects of the climatology of China." Hawaii. Univ., Honolulu, Dept. of Meteorology, UHMET.

China lies on the edge of the largest continent and beside the largest oceans (the Pacific and Indian oceans), with the highest plateau (the Tibetan Plateau) in its southwestern part. A monsoon climate prevails over most of China. The annual change in weather and climate is obvious and complicated. In winter, the Mongolia-Siberia cold high pressure predominates. Its ridge extends southward and controls most of China, with frequent cold outbreaks. The winter climate is characteristically cold and dry. Spring is a transition season. Temperature rises gradually but unevenly. Weather is variable, with cyclone activity over the Yangtze-Huaihe River and northeastern China. Usually, a rainy period persists over southern China; gales and frequent spring droughts occur over northern China. Summer is hot and wet. For the whole country, the rainy season begins in April and ends in Sept.-Oct. The first rainy season (mei-yu) over southern China occurs in May to early June; over the Yangtze-Huaihe River, it is usually confined between late June and early July. The midsummer rainy season in northern China appears in late July to early Aug. Typhoons and other tropical weather systems introduce the second rainy season in southern China from July to Sept. Usually, heavy rains and, on occasion, extremely heavy rains may fall anywhere in China during the rainy season and cause serious floods. However, a failure of the mei-yu rainy season and control by the subtropical high can cause a sweltering hot summer and drought, with disastrous consequences. Eastern and southern China suffer typhoon strikes in summer.

Barry, R. G. and R. J. Chorley (1998). "Atmosphere, weather & climate, seventh edition." London, UK, Routledge 409.

The sixth edition of this text responded to the recognition of the reality and possible effects of human activities on the environment, as well as to other current scientific advances, by the most extensive revision to date. New sections were added on acid precipitation, the Walker circulation, modelling the atmosphere-earth-ocean system, the climates of Amazonia and southern Africa, tropical urban climates, recent climatic changes, forcing and feedback mechanisms of the atmosphere-earth-ocean system, anthropogenic changes in atmospheric composition and in the greenhouse effect, as well as on model predictions of climate and associated environmental changes which might be expected during the twenty-first century. Additional material was provided on the greenhouse effect, aerosols, ozone, the carbon cycle, global cloud cover, the thermal role of the oceans, the exosphere and the magnetosphere, orographic precipitation, aerodynamic roughness and airflow over topographic obstructions, medium- and long-range forecasting, wind activity over Western Europe, hurricanes, Asian monsoon mechanisms, monsoon depressions, the timing intensity and phases of the Asian summer monsoon, the West African monsoon, tropical forest climatology, urban pollution, urban climatology, and Pleistocene climatic changes. SI units of energy flux density were used throughout and some ninety new or redrawn figures and tables were included. This updated and expanded seventh edition, having undergone an equally rigorous revision, provides a comprehensive introduction to weather processes and climatic conditions. Beginning with an extended treatment of atmospheric composition and energy, stressing the heat budget of the Earth and the causes of the greenhouse effect, the authors turn to the manifestations and circulation of atmospheric moisture, including atmospheric stability and precipitation patterns in space and time. A consideration of atmospheric and oceanic motion on small to large scales and modelling of general circulation leads to a discussion of the structure of air masses, frontal cyclones and weather forecasting on different time scales. The treatment of weather and climate in temperate latitudes begins with studies of Europe and America, extending to the conditions of their subtropical and high-latitude margins and includes the Mediterranean, Australasia, North Africa, the southern westerlies, and the sub-arctic and polar regions. Tropical weather and climate are also described through an analysis of the climatic mechanisms of monsoon Asia, Africa, Australia and Amazonia, together with the tropical margins of Africa and Australia and the effects of ocean movement and the El Nino-Southern Oscillation and teleconnections. Small scale climates--including urban climates--are considered from the perspective of energy budgets. The final chapter has been completely updated and rewritten to stress the structure and operation of the atmoshere-earth-ocean system and the causes of its climate changes. A discussion of the various modelling strategies adopted for the prediction of climate change is undertaken, in particular relating to the IPCC 1990-95 models. A consideration of certain other environmental impacts of climate change is also included.

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

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

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

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

Basu, G. C. (2001). "An unusually northern position of ITCZ during the last week of april (21-26 april) 1999 and associated weather over Tamilnadu and Kerala." Mausam 52(4): 733-735.

The semi permanent wind discontinuity/trough line in the lower troposphere over southern peninsula running from north to south is the main cause of thundershowers over Kerala in the summer months of March to May. Cyclonic circulations moving across the extreme south peninsula from east to west can also cause rainfall over Kerala as pointed by Lakshminarayanan (1998). While studying heavy rains in Kerala during the southwest monsoon Julius Joseph et al. came to the conclusion that "presence of tropical storms in and around Gulf of Tonkin in south China Sea strengthens the monsoon westerlies over Kerala and Kerala experiences active/vigorous monsoon conditions." They also noted that "simultaneous presence of low pressure systems in the north Bay of Bengal and Gulf of Tonkin more conducive for heavy rainfall over Kerala in monsoon months.

Beresford, A. K. C. and G. O'Hare (1999). "A comparison of two heavy rainfall events in India: Bombay, 24 July 1989, and Cherrapunji, 12 June 1997." Weather, Bracknell, England 54(2): 34-43.

This paper aims to compare two weather events that took place during the Indian summer monsoons of 1989 and 1997. The two events were experienced first-hand by the authors and are shown to exhibit some similarities, such as their close association with low pressure and tropospheric air instability during the summer monsoon season, and the magnitude and intensity of the rainfall on the two occasions. The two rainfall episodes were very different, however, in the detail of their precipitation mechanisms and in the impact that the events had on the local community. The first event was an extremely vigorous tropical storm which hit the coast of Maharashtra on 24 July 1989 with hurricane force winds and torrential rain. The second event, yielding a similar daily rainfall total to the first, took place on 12 June 1997 when a typical Assam deluge was observed and its features were noted. Events at Bombay made headline news, not only in India but also abroad; events at Cherrapunji passed by almost unnoticed with the expectation that they would be repeated many times each year.

Bhalme, H. N. and D. A. Mooley (1981). "Cyclic fluctuations in the flood area and relationship with the double (Hale) sun-spot cycle." Journal of Applied Meteorology, Boston 20(9): 1041-1048.

An objective numerical index was used to obtain, on the dryness side, the family of Drought Area Indices (DAI) and, on the wetness side, the family of Flood Area Indices (FAI) for India for the period 1891-1979. Three series of the DAI family are the percentage areas of India corresponding to mean monsoon index for a given year: less than or equal to -1 (mild drought or worse); less than or equal to -2 (moderate drought or worse); and less than or equal to -3(severe drought or worse). On the wetness side, three series of the FAI family are the percentage areas of India corresponding to mean monsoon index for a given year: greater than or equal to +1(mild flood or worse); greater than or equal to +2(moderate flood or worse); greater than or equal to +3(severe flood or worse). Power spectrum analysis of the DAI series shows a high-frequency peak that is probably associated with the quasi-biennial oscillation. Spectrum and cross-spectrum analysis of the FAI series and sun-spot numbers of the double (Hale) sun-spot cycle reveal that a highly significant similar to 22-yr cycle in the FAI is nearly in phase with the double sun-spot cycle and that they are interrelated. Harmonic dial analysis shows that all of the large-scale flood events over India occurred consistently in the major sun-spot cycle, suggesting an association of large-scale flood recurrence over India with the double sun-spot cycle. The strong evidence of the relationship between areal extent of flood over India and the double sun-spot cycle reported shares in the kind of relationship reported for the western U.S. but in the opposite sense of weather characteristics: i.e., for flood rather than drought.

Bhowmik, S. K. R. and P. K. Mishra (1999). "Some structural characteristics of pre-monsoon depression in the Bay of Bengal." Mausam 50(1): 19-24.

During the period 6 to 16 May, 1995, three deep depressions formed one after another over west Bay of Bengal and moved from south to north. In this paper, structural characteristics of these systems are investigated from the distribution of thermal and thermodynamical field observed around the depression center utilising daily Rs/Rw and other available coastal observations during the period. Major findings of the study are: (i) The depressions have low level cold core and middle and upper tropospheric warm core. (ii) Thermal and moisture fields tilt north ward with height but vertical tilt of contour height is not uniform at all levels. (iii) During intensification of the system significant increase in temperature and moisutre occurs above 700 hPa and significant fall of contour height occurs below 300 hPa.

Bhowmik, S. K. R. and K. Prasad (2001). "Some characteristics of Limited-Area Model-Precipitation forecast of Indian monsoon and evaluation of associated flow features." Meteorology and Atmospheric Physics 76(3-4): 223-236.

The Florida State University based Limited-Area Model is in operational use at India Meteorological Department, New Delhi. This paper assesses the performance of the model in temporal and spatial scale to provide 24 hours rainfall forecast over Indian region during south-west monsoon (June to September) and north-east monsoon season (October and November) using three years data (1997-1999). Characteristic features of mean flow pattern produced by the forecast (24 hours) are also examined comparing them with the corresponding analysis fields. The study demonstrates that performance of the numerical model in predicting precipitation varies with month, geographic location and by synoptic regime. The model, in general, is able to reproduce the spatial pattern of monthly and seasonal rainfall but under-estimates orographic rainfall and over estimates rainfall associated with the monsoon low pressure systems. In October and November when the low pressure belt shifts to the southern latitudes of India, the model is able to capture the heavy rainfall zone confined over south Peninsula. Time series and categorical statistics show that there is a very good correspondence between observed and predicted rainfall. The other important characteristic features of south west monsoon are well captured by the model and are comparable with the analysis field. But some of the significant deficiencies noticed in the forecast are: higher mean sealevel pressure, particularly over the domain of heat low and relatively weaker lower tropospheric westerlies. The results of this paper will provide useful input on model performance to operational forecasters and model developers.

Biqi, L. and L. Sichen (1989). "The contribution of heating effect to the vertical circulation of the monsoon depression over the Southern China Sea." Acta Meteorologica Sinica, Peking 47(3): 364-370.

The detail diagnostic analyses are made on two cases of monsoon depression over the Southern China Sea by using FGGE3B data (no initialization), the diagnostic balance model (Krishnamurti, 1968) and the cumulus parameterization scheme (Kuo, 1974). The vertical circulation evolution of the depression in the process of its genesis and development is contrasted in both cases, with and without diabatic heating. Meanwhile the studies are also made for the contribution of latent heat to the vertical circulation. The results show that the large-scale heating effect only plays a main role to the initial vertical motion field, and the cumulus heating effect is a main factor to the strengthening and maintaining of the depression vertical circulation.

Bishnoi, O. P. (1984). "Crop moisture index in characterizing the agricultural drought at Hissar." Mausam, New Delhi 35(3).

Because soil moisture measurements are not available on a large scale, the meteorological budgeting technique has been utilized in formulating a crop moisture index to explain the behavior of agricultural drought--its intensity, duration, and severity for six different monsoon rainfall years at Hissar station. A thorough test of the Palmer crop moisture index has also been made in explaining the behavior of rainfall crops during the six monsoon years 1971-1976. The Palmer crop moisture index fails to explain the behavior of crop conditions in the area under study; therefore, it was necessary to formulate a new crop moisture index to explain the crop conditions in accordance with results obtained in the experimental plots under dryland agriculture. The weekly crop moisture indexes better depict the crop conditions and can be used successfully to predict the crop outlook over a large area. Also, on the basis of crop moisture conditions, various precautionary measures and agronomic practices are indicated for practical use when the southwest monsoon is apparently difficult to predict because of the complex monsoon system. Agricultural drought is classified as extremely dry, dry, semi-dry, normal, moist, wet, and extremely wet on the basis of crop moisture index values ranging from 0 to >4.01 during the growing season of the crop. The crop moisture index--its intensity, duration, and rhythm in space and time--has been very helpful in explaining the role of agronomic practices and has the potentiality to explain the crop yield variations.

Biswas, B. C. and P. S. Nayar (1984). "Quantification of drought and crop potential." Mausam, New Delhi 35(3): 281-286.

The dry farming region in India, where annual rainfall varies from 40 to 100 cm, includes 105 districts in nine states. In this region, rainfall is the limiting factor for successful raising of crops. In order to stabilize the crop at a certain level, even in a low rainfall year, it is essential to know the frequency of drought years so that agriculture may be planned on a rational scientific basis. For this purpose, it is necessary to know the minimum week-by-week rainfall at different probability levels. The lowest amount of rainfall at different probability levels (10-90%) is computed by fitting an incomplete gamma-distribution probability model to weekly rainfall totals of 87 stations in the dry farming region during the Indian monsoon season. The same amount of rainfall behaves differently, in terms of water availability to plants, depending upon atmospheric demand. A moisture availability index (MAI), which is defined as the ratio of probabilistic rainfall for a week to potential evapotranspiration, has been computed. A crop requries different amounts of water at its various growing phases, and at least one third of the potential demand is necessary in the early stage. The moisture availability index at the 50% level is used to map out drought-prone areas. The period when MAI greater than or equal to 0.3 is taken as the crop growing period. The midseason water stress period (MAI less than or equal to 0.3) is found from the 50% probability level, and this period is used to map out drought-prone areas, in both time and space. The drought severity is classified according to the number of water stress periods and their durations. Drought proneness is also discussed at other probability levels. By applying the present criteria, the drought-prone area in the dry farming tract has been demarcated in both time and space. A drought prone area is found which extends from Aurangabad in Maharashtra to Bangalore in Karnataka. Drought is frequent in Gujarat and eastern Rajasthan.

Bitan, A. and H. Sa'aroni (1992). "The horizontal and vertical extension of the Persian Gulf Pressure Trough." International Journal of Climatology, New York, NY 12(7): 733-747.

The Persian Gulf Barometric Trough is an extension of the southwest Asian Monsoon. It starts in the middle of June, stabilizing by the end of the month, remaining dominant during July and August and disappears very quickly in mid-September. Because of its thermal origin its height is limited to about 1500 m. Above it dominates, during the summer months, the subtropical high-pressure system with its Azores extension covering the Mediterranean region. The transitional zone between these two pressure systems is an inversion zone, whose lower base sometimes reaches the mountain tops of Israel and even lower. On such occasions the daily maximum temperatures are higher at the stations in the mountains than in the coastal plain. Because of its thermal origin, it was expected that diurnal changes of temperature must affect the horizontal and vertical extension of the Persian Gulf Trough. However, the diurnal fluctuations of the pressure are mainly remarkable at stations at the margin of the trough, while at those stations affected directly by it, the daily fluctuations are minimized by irregular periodic changes in the intensity of the Persian Trough occurring every few days. These changes are due mainly to fluctuations of the upper level high-pressure system. Changes in the position of the Persian Trough influence greatly the daily weather in the Levant.

Boon, K. C. (1984). "Malaysia: effects of the intrusion of mid-latitude systems into southeast Asia." WMO Tropical Meteorology Research Programme.

This report summarizes problems on tropical and mid-latitude interactions over the South China Sea identified previous to the northern Winter Monsoon Experiment (Winter MONEX), as well as new findings derived from research studies conducted after the Winter MONEX. Winter MONEX was conducted from 1 December 1978 to 31 March 1979, consisting of many studies on the synoptic- and planetary-scale monsoon phenomena. Findings from the Winter MONEX study include: the northeastern corner of the Tibetan Plateau is the birthplace of a small-scale low-level cyclone trapped below 700mb; responses to transient forcing (monsoon surges) are mainly in Rossby, Kelvin, inertia-gravity, and mixed Rossby-gravity modes; the northeasterly cold surge enhances deep convection in front of an equatorial cyclonic vortex, and weakens the deep cumulus convection afterward; the tropics and extratropics cannot be thought of as isolated regions; and the Asian monsoon is a continuous heat source from which there emanates a planetary scale regime dominating most of the eastern hemisphere. In a recent study, tropical storm activity over the West Pacific interacting with a cold surge is found to suppress convective activity over the Malaysia-South China Sea region.

Boyle, J. S. (1986). "Comparison of the synoptic conditions in midlatitudes accompanying cold surges over Eastern Asia for the months of December 1974 and 1978, Pt. 2, Relation of surge events to features of the longer term mean circulation." Monthly Weather Review, Boston 114(5): 919-930.

This paper deals with midlatitude initiation of East Asian cold surges. The effects of individual cold surges on the circulation on the East Asian coast are studied for Dec. 1974 and Dec. 1978. These months represent a contrast with regard to the strength of cold surges occurring in that month. The surges occuring in Dec. 1978 were weak, those in 1978 were strong. The circulation features and processes considered were 1) the 200-mb zonal momentum budget, 2) the 400-mb frontogenesis forcing, 3) the low-level meridional eddy heat fluxes, and 4) the thermally direct circulation cell in the entrance region to the East Asian jet maximum. The times of the surge events are shown to be periods that dominate in computing the longer term monthly statistics of these circulation features. The monthly mean features computed are also typical of other studies using even much longer term winter averages. The implication is that surges also dominate these statistics, and long-term averages of the East Asian winter monsoon circulation at the midlatitudes and subtropics are dominated by the surge characteristics. During the cold surge event, the balance of the 200-mb zonal momentum budget is between the zonal advection of momentum and the Coriolis acceleration. Between the events, the balance is mixed, with no terms clearly dominating. The climatological maximum in confluence at 400 mb (quasi-geostrophic frontogenesis) found over East Asia seems to be, for the most part, the result of intensified confluence accompanying the surge event. This frontogenesis is necessary for the temperature field to remain in thermal wind balance with the accelerating jet. There is also marked low-level frontogenesis occurring at lower levels as the cold air sweeps southward. The low-level eddy heat fluxes, which have a large maxima on the East Asian coast, are shown by time-longitude plots to be largely the results of the surge circulation. Cold air is continuously moving southward in the Asian winter monsoon, but the surge fluxes are intense and are focused on the coast. The thermally direct circulation cell in the entrance region to the East Asian jet maximum reaches its peak intensity during the cold surges. The two months show similar patterns, only the intensity of the circulation is somewhat reduced in the month of the weaker surges (Dec. 1978). Evidently, the same processes are at work during the surges of each month only at reduced levels in Dec. 1978.

Boyle, J. S. and T. J. Chen (1987). "Synoptic aspects of the wintertime East Asian monsoon." Chang, Chih Pei.

This discussion of the synoptic aspects of the winter East Asian monsoon deals with East Asia to the region east of 100 degrees E, specifically excluding the winter Indian monsoon, and with a time scale of the circulation features on the order of 2-6 days and with horizontal scales of similar to 3000 km. The climatology of the area considered is presented, with regard to winter mean fields of 200 mb and surface wind fields, mean sea level pressure and 500-mb heights, cyclones, anticyclones, and frontal zones. Cold surges of eastern Asia during winter are described by using synoptic and dynamic aspects of a specific example. Cyclones and cyclogenesis, sensible and latent heating effects, intermediate cyclones of the East China Sea, orographic effects, and explosive cyclogenesis off the East Asian coast are discussed.

Burlutskiy, R. F. (1976). "Causes of the monsoon onset burst and boundaries of the monsoon rain area in the Indian Ocean." Symposium on Tropical Monsoons, Poona, India, Sept.

The monsoon behavior, beginning with the main features of the atmospheric circulation and weather in May-June 1973 and then proceeding to the burst of the monsoon on June 4-5, is discussed on the basis of data of the U.S.S.R.-India expedition ``Monsoon-73.'' The characteristics of the monsoon are considered to be the result of the effect of the Tibetan Plateau upon the air motion near the axis of the subtropical high pressure belt. The principal stages of this effect are described.

Carr, L. E., III, M. A. Boothe, et al. (1997). "Observational evidence for alternate modes of track-altering binary tropical cyclone scenarios." Monthly Weather Review, Boston, MA 125(9): 2094-2111.

An observational study of western North Pacific tropical cyclones (TC) revealed many cases of two TCs whose tracks were altered by processes that were quite different from the mutual advection (Fujiwhara-type) processes. Thus, four conceptual models are proposed to describe these track alterations. A conceptual model called direct interaction is proposed that is a modification of one by Lander and Holland and has three modes: 1) a one-way influence in which the track of a smaller TC that is embedded in the circulation of a larger TC has a cyclonic orbiting motion, but no significant track alteration of the larger TC is apparent; 2) a similar case in which a mutual advection occurs with the tracks of both the smaller and larger TCs being altered; and 3) a subset of 2) in which the mutual advection includes an attraction component such that the two similarly sized TC circulations eventually merge into a larger circulation with a single center. During the 7-yr period (1989-95), the one-way influence, mutual interaction, and merger modes were detected seven, three, and two times. A semidirect interaction conceptual model is proposed in which the two TCs have a relative cyclonic rotation as in the Lander and Holland model, but the TCs are separated by 10 degrees -20 degrees longitude so that a direct (advective-type) interaction is excluded. Rather, the track alteration is attributed to an environmental flow established by the juxtaposition of a TC on one side and a subtropical anticyclone cell on the opposite side. In an east-west orientation of the two TCs and a subtropical anticyclone cell to the east (west), the height gradient between the western (eastern) TC and the eastern (western) subtropical anticyclone establishes a poleward (equatorward) environmental steering flow across the eastern (western) TC. In the 1989-95 sample, a semidirect interaction that altered the tracks of the eastern or the western TC occurred 18 and 14 times, respectively. An indirect interaction conceptual model is proposed in which the distinguishing feature is the Rossby wave dispersion-induced anticyclone to the east and equatorward of the western TC. This anticyclone imposes an equatorward (poleward) steering flow across the eastern (western) TC. Several variations of the indirect interaction are possible depending on the separation distance, sizes of each TC, and their relative orientation. During the 7-yr period, an indirect interaction affecting the western TC or the eastern TC occurred 36 and 22 times, respectively. A fourth conceptual model of track alterations involving two TCs is proposed in conjunction with a reverse-oriented monsoon trough formation. The distinguishing feature of this conceptual model is the combination of the peripheral anticyclones of both TCs as the eastern TC moves into an east-west orientation and has a separation of 10 degrees -20 degrees longitude. In the 1989-95 sample, a reverse-oriented trough formation involving two TCs occurred seven times. The frequency of track alterations whenever two TCs are present emphasizes that forecasters must give special attention to such situations. The four conceptual models proposed here emphasize that the physical mechanisms are complex and in the vast majority of cases cannot be attributed to the mutual advection (Fujiwhara-type) process implied in the Lander and Holland model.

Carr, L. E., III and R. L. Elsberry (1995). "Monsoonal interactions leading to sudden tropical cyclone track changes." Monthly Weather Review, Boston, MA 123(2): 265-289.

Sudden poleward track changes of tropical cyclones embedded in monsoon gyres in the western North Pacific are documented. During these track changes, which are generally not well forecast, the cyclones are often accompanied by a separate comma-shaped area of gale-force winds and deep convection along the eastern periphery. This monsoon surge is distinct from the tropical cyclone. Synoptic analyses often reveal a building anticyclone to the east or southeast of the monsoon gyre. The hypothesis that the sudden track change is initiated by a binary interaction of the tropical cyclone and monsoon gyre is tested with a nondivergent barotropic model. Tropical cyclone-scale vortices with initial positions within the eastern semicircle of a larger monsoon gyre-scale vortex initially coalesce with the monsoon gyre and then exhibit sudden poleward track changes that are similar to the observations. During the coalescence phase, the large and relatively weak monsoon gyre undergoes a beta -induced dispersion in which nonlinear voticity advection also plays an important role. This dispersion process produces strong ridging to the east and southeast of the coalesced tropical cyclone and monsoon gyre. An intermediate region of high winds that resembles the observed monsoon surge develops between the monsoon gyre and the peripheral ridging. A southerly steering develops across the coalescing tropical cyclone and monsoon gyre and causes the poleward acceleration. Key features of the simulated streamfunction and isotach patterns associated with the sudden track changes are substantiated with synoptic analyses of observed cases with similar track changes. Thus, it is concluded that the tropical cyclone-monsoon gyre interactions are a likely explanation for monsoon surge track changes and that the observed phenomena may be explained to first order by conservation of absolute vorticity on a beta plane.

Chang, C. P., J. E. Erickson, et al. (1979). "Northeasterly cold surges and near-equatorial disturbances over the winter MONEX area during December 1974, Pt. 1, Synoptic aspects." Monthly Weather Review, Boston 107(7): 812-829.

This paper describes a pre-winter monsoon experiment (Winter MONEX) pilot study, the purpose of which is to examine the possible interactions between the northeasterly cold surges off the continent of Asia and the convective disturbances in the near equatorial region. Based on surface and 850-mb wind and temperature analyses, satellite data, and synoptic weather charts of the Hong Kong Royal Observatory, a sequence of synoptic events associated with two cold air surges and near-equatorial disturbances over the Winter MONEX area of the South China Sea and its vicinity during Dec. 1974 is discussed. The results lead to the tentative conclusions that, because of the varying degree of air-sea interactions between cold air originating from the southeastern China coast, Taiwan, and the Luzon Straits, and that originating from the South China coast, the near-equatorial latitudes of the South China Sea will experience a freshening of the low-level northeasterly monsoon winds prior to a decrease in surface temperature which, if it occurs, is confined to the western portion of the South China Sea. This permits a near-equatorial disturbance (which may have originated from the semi-stationary, near-equatorial trough over the coast of North Borneo or from a westward propagating wave in the western Pacific) to be intensified at an early state of the surge by enhanced low-level convergence and organized deep cumulus convection. Afterward it may be weakened by either the cold air incursion along the Vietnam coast or a slackening of the northeasterlies.

Chang, C. P. and K. G. Lum (1985). "Tropical-midlatitude interactions over Asia and the western Pacific Ocean during the 1983/84 northern winter." Monthly Weather Review, Boston 113(8): 1345-1358.

Previous studies of cold surges during the northern winter monsoon suggested a short-term midlatitude-tropical interaction such that the variations of the midlatitude jet over East Asia correspond to variations in tropical convection. However, because cold surges occur during periods of intensified baroclinicity, it is possible that the strengthening of the jet may be due entirely to midlatitude baroclinic development rather than the enhanced local Hadley circulation forced by the increase in tropical convection. In this study, objectively analyzed 200-mb wind data for the 1983 /1984 winter are examined to address the problem of determining cause and effect in short-term midlatitude-tropical interactions. Significant positive correlation between the midlatitude jet acceleration and tropical divergence was found in several regions in the Asia-Pacific-Indian Ocean region. Among six major intensifications of the East Asian jet streak maximum during Dec. 1983, three were related to tropical cyclone activity and two to cold surges. The tropical cyclone cases led to the conclusion that the midlatitude jet can be influenced effectively by tropical convective activity on a day-to-day basis. This result has possible implications for midlatitude weather forecasting. The study also confirmed the downstream propagation of the strengthened jet streaks, which is probably due to self-advection, and the existence of thermally indirect circulations at the exit region of the jet, in both the time-mean and the transient motion fields.

Chang, F. C. and E. A. Smith (2001). "Hydrological and Dynamical Characteristics of Summertime Droughts over U.S. Great Plains." Journal of Climate 14(10): 2296-2316.

A drought pattern and its time evolution over the U.S. Great Plains are investigated from time series of climate divisional monthly mean surface air temperature and total precipitation anomalies. The spatial pattern consists of correlated occurrences of high (low) surface air temperature and deficit (excess) rainfall. The center of maximum amplitude in rain fluctuation is around Kansas City; that of temperature is over South Dakota. Internal consistency between temperature and precipitation variability is the salient feature of the drought pattern. A drought index is used to quantify drought severity for the period 1895-1996. The 12 severest drought months (in order) during this period are June 1933, June 1988, July 1936, August 1983, July 1934, July 1901, June 1931, August 1947, July 1930, June 1936, July 1954, and August 1936. Hydrological conditions are examined using National Centers for Environmental Prediction (NCEP) reanalysis precipitable water (PW) and monthly surface observations from Kansas City, Missouri, and Bismarck, North Dakota, near the drought centers. This analysis explains why droughts exhibit negative surface relative humidity anomalies accompanied by larger than normal monthly mean daily temperature ranges and why maximum PWs are confined to a strip of about 10 degree longitude from New Mexico and Arizona into the Dakotas and Minnesota. Dynamical conditions are examined using NCEP reanalysis sea level pressures and 500- and 200-mb geopotential heights. The analysis indicates a midtroposphere wave train with positive centers situated over the North Pacific, North America, and the North Atlantic, with negative centers in the southeastern Gulf of Alaska and Davis Strait. Above-normal sea level pressures over New Mexico, the North Atlantic, and the subtropical Pacific along with below-normal sea level pressures over the Gulf of Alaska eastward to Canada, Davis Strait, and Greenland are present during drought periods. The most prominent feature is the strong anticyclone over central North America. On a regional scale, midtropospheric westerly winds are weakened (or become easterly) south of a thermal heat low centered in South Dakota during drought episodes because of the north-south temperature reversal perturbation. The associated westward displaced Bermuda high leads to enhanced low-level warm flow into the Dakotas, thus helping to maintain the reversal in the meridional temperature gradient and the concomitant thermal wind reversal. Enhanced moisture transport from the Gulf of California into the western plains (part of the Great Basin monsoon process) results from the large-scale perturbation pressure pattern. Middle-upper level convergence maintains the water vapor strip east of the Rocky Mountains, while the Mississippi valley undergoes moisture cutoff from both this process and the westward shift in the Bermuda high. The strip of maximum PW then undergoes enhanced solar and infrared absorption that feeds back on the thermal heat low. Surface air temperatures warm while sinking motion balances middle-upper level radiative cooling around the Kansas City area. This is the dynamical coupling that leads to reduced surface relative humidities. The centers of high surface air temperature and deficit rainfall are dynamically consistent with patterns in geopotential heights, vertical velocities, and water vapor amounts.

Chang, F.-C. and E. A. Smith (2001). "Hydrological and dynamical characteristics of summertime droughts over U.S. Great Plains." Journal of Climate, Boston, MA 14(10): 2296-2316.

A drought pattern and its time evolution over the U.S. Great Plains are investigated from time series of climate divisional monthly mean surface air temperature and total precipitation anomalies. The spatial pattern consists of correlated occurrences of high (low) surface air temperature and deficit (excess) rainfall. The center of maximum amplitude in rain fluctuation is around Kansas City; that of temperature is over South Dakota. Internal consistency between temperature and precipitation variability is the salient feature of the drought pattern. A drought index is used to quantify drought severity for the period 1895-1996. The 12 severest drought months (in order) during this period are June 1933, June 1988, July 1936, August 1983, July 1934, July 1901, June 1931, August 1947, July 1930, June 1936, July 1954, and August 1936. Hydrological conditions are examined using National Centers for Environmental Prediction (NCEP) reanalysis precipitable water (PW) and monthly surface observations from Kansas City, Missouri, and Bismarck, North Dakota, near the drought centers. This analysis explains why droughts exhibit negative surface relative humidity anomalies accompanied by larger than normal monthly mean daily temperature ranges and why maximum PWs are confined to a strip of about 10 degrees longitude from New Mexico and Arizona into the Dakotas and Minnesota. Dynamical conditions are examined using NCEP reanalysis sea level pressures and 500- and 200-mb geopotential heights. The analysis indicates a midtroposphere wave train with positive centers situated over the North Pacific, North America, and the North Atlantic, with negative centers in the southeastern Gulf of Alaska and Davis Strait. Above-normal sea level pressures over New Mexico, the North Atlantic, and the subtropical Pacific along with below-normal sea level pressures over the Gulf of Alaska eastward to Canada, Davis Strait, and Greenland are present during drought periods. The most prominent feature is the strong anticyclone over central North America. On a regional scale, midtropospheric westerly winds are weakened (or become easterly) south of a thermal heat low centered in South Dakota during drought episodes because of the north-south temperature reversal perturbation. The associated westward displaced Bermuda high leads to enhanced low-level warm flow into the Dakotas, thus helping to maintain the reversal in the meridional temperature gradient and the concomitant thermal wind reversal. Enhanced moisture transport from the Gulf of California into the western plains (part of the Great Basin monsoon process) results from the large-scale perturbation pressure pattern. Middle-upper level convergence maintains the water vapor strip east of the Rocky Mountains, while the Mississippi valley undergoes moisture cutoff from both this process and the westward shift in the Bermuda high. The strip of maximum PW then undergoes enhanced solar and infrared absorption that feeds back on the thermal heat low. Surface air temperatures warm while sinking motion balances middle-upper level radiative cooling around the Kansas City area. This is the dynamical coupling that leads to reduced surface relative humidities. The centers of high surface air temperature and deficit rainfall are dynamically consistent with patterns in geopotential heights, vertical velocities, and water vapor amounts.

Chang, K.-H., F.-T. Jeng, et al. (2000). "Modeling of long-range transport on Taiwan's acid deposition under different weather conditions." Atmospheric Environment, Oxford, England 34(20): 3281-3295.

The long-range and transboundary transport of acid deposition precursors in East Asia has become an important issue due to the industrial development in this area in recent years. To represent an entire year's impact by long-range transport for Taiwan's acid deposition, six episodes in 1993 were selected for study using Taiwan Air Quality Model, which was developed on the basis of the Regional Acid Deposition Model system. The six episodes cover five types of weather conditions including the Northeasterly monsoon, Spring stationary front, Mei-Yu front, Summer shower, and Autumn front. Two emission conditions were simulated for each episode to quantify the long-range transport effect. One condition takes all emissions within the simulated domain into account as a base case, while another condition excludes Taiwan's emission and considers all of the other emissions as a control case. The results of the present study indicate that contributions of long-range transport to Taiwan's sulfur depositions range from 9 to 45% and nitrogen depositions from 6 to 33% for the six episodes. The most serious effect of long-range transport is the northeasterly monsoon episode for both total sulfur and total nitrogen deposition. The entire year contribution by long-range transport is estimated to be 39% for wet sulfate deposition, and 37% for wet nitrogen deposition for Taiwan.

Cheang, B. K. (1977). "Synoptic features and structures of some equatorial vortices over the South China Sea in the Malaysian region during the winter monsoon, December 1973." Pure and Applied Geophysics, Basel 115(5/6): 1303-1333.

In Dec. 1973, peninsular Malaysia and Sarawak experienced a few periods of heavy rain caused by westward moving equatorial vortices from the South China Sea. The synoptic characteristics associated with the development and intensification of these vortices are shown. The structure of one of the disturbances was examined. Disturbances in the trades associated with lateral shear were important for the genesis of the equatorial vortices; however, the intensification of these disturbances depended upon the interaction with the cold monsoon surge.

Cheang, B. K. and T. N. Krishnamurti (1980). "Middle latitude interactions during the winter monsoons." Florida. State Univ., Tallahassee, Dept. of Meteorology, Report(80).

The authors identify a sequence of phenomenological events that lead to dry or wet spells over the general region of the South China Sea during the winter monsoon. During the wet spells, the sequence identifies interactions among eastward propagating downstream amplification over the midlatitude middle troposphere; meridional oscillation of sea level high pressure cells; westward moving downstream amplification and associated wave propagation over the tropical lower troposphere; and modulation of monsoon rainfall by westward propagating tropical waves. During dry spells, the sequence is somewhat dissimilar. A phase shifted development of intense upper level system over the middle latitudes produces a different response in low latitudes: the downstream amplifying system of the middle latitudes results in an intense trough around 90 degrees E, 140 degrees E, and 170 degrees W; westerlies penetrate far southward in the middle troposphere over the Asian-West Pacific sector; the Pacific high moves far southward; and quasi-stationary features prevail in the latitude belt 5 to 10 degrees N and are usually only disrupted by another readjustment of the middle latitude systems.

Chen, G. (2000). "Influences of winter-strengthen pattern and winter-weaken pattern of El Nino and La Nina on drought/flood in summer over China." Quarterly Journal of Applied Meteorology, Beijing, China 11(2): 154-164.

According to the inter-monthly SSTA variation during winter in equatorial East Pacific after the occurrings of El Nino and La Nina onset, the winter-strengthen pattern and winter-weaken pattern of El Nino and La Nina are defined. The characteristics of the general circulation in winter, spring and summer, East Asian monsoon, summer rainfall and the distribution of drought/flood in China are discussed. It is shown that the four kinds of patterns for summer rainfall and drought/flood in China could be associated with different phases of ENSO cycle during winter, and with different responses of the general circulation and East Asian monsoon to that. Finally, a physics concept pattern is proposed about the rainfall distribution patterns in summer over China which are associated with different patterns of El Nino and La Nina in winter as well as the general circulation and the East Asian monsoon.

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

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

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

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

Chen, L., Y. Sun, et al. (2000). "The analysis of weather pattern in the heavy rain process over Songhuajiang and Nenjiang in 1998." Meteorological Monthly, Beijing, China 26(10): 19-23.

The weather circulation pattern of the summer tight precipitation period and the main heavy rain course in 1998 were analyzed with the NCAR/NCEP and daily precipitation data from 94 surface stations in Songhuajiang and Nenjiang area. The continuous rainfall can be contributed to the following weather patterns: (1) the steady blocking pattern in the middle and high latitude of Asia, (2) controlled by cold vortex long term, (3) advancing north ward of the subtropical high over the west Pacific and its suitable position, (4) the strong monsoon in midsummer.

Chen, L. and X. Xu (1991). "Progress on TIbetan Plateau field EXperiment (TIPEX) and its research programme." Annual Report, Beijing, China.

This paper is going to review the major research achievements of TIPEX in the period of pre-study. These achievements include five components as follows: physical process of the Tibetan Plateau and its parameterization; the impacts of the Tibetan Plateau on the general circulation; the impacts of thermal process of the Tibetan Plateau on Asian monsoon circulation; the impacts of Plateau physical process on global climate change; impacts of Plateau physical process on disastrous weather systems over East Asia. Apart from the pre-study, this paper will also review the major progress of preparatory technical aspects related to observation system planning, data processing, modeling, as well as technical collaboration.

Chen, Q., Z. Zhao, et al. (2000). "Study on the features of flood/drought and activities of typhoons over East China Sea and their linkage to ENSO in warm/cool summers." Quarterly Journal of Applied Meteorology, Beijing, China 11(1): 88-94.

By using the data of temperature, precipitation and typhoon year book from 1951 to 1995, the warm and cool summers are defined and identified, and features of monsoon rainband distribution and the abnormal activities of typhoons over the East China Sea as well as their linkages to ENSO are statistically analyzed. The results show that the activities of typhoons and the monsoon rainband distribution in warm summers are very different from those of cool summers. Meanwhile, the SSTA over equatorial Pacific exhibits distinctively contrast during warm summers and cool summers. In addition, the physical concept model about the teleconnection is given.

Chen, T., M. Yen, et al. (2002). "An East Asian Cold Surge: Case Study." Monthly Weather Review 130(9): 2271-2291.

Since a cold surge is a hazardous weather phenomenon in east Asia, the rapid population increase and economic growth over the past two decades require improvement in forecasting cold surges and their related weather events over this region. However, without a better understanding of these events, this task cannot be accomplished. A cold surge with a well-defined cold front passing through Taiwan was selected to illustrate its impact on the east Asian weather system. This case is typical of a large portion of surges occurring in the region. Major findings of this study are as follows. Coupling with the upper ridge-trough structures of the wave train straddling the eastern seaboard of northeast Asia, cold surges occur sequentially. A cold front with a prefront high pressure zone is formed by the new surge outflow interacting with the anticyclone of the aging surge. The warm moist air advected northeastward along the cold front assists the development of the new surge's low center, while the prefront high pressure zone facilitates the formation of a double-cell structure in the local Hadley circulation. The southeastward propagation of the cold front is driven by the eastward-propagating short-wave trough through the couplets of both new and aging cold surges. The surface weather conditions in the low-elevation zones of Taiwan are modulated by the cold surge flow, but the high-elevation areas may be affected instead by the tropical southeast Asian high. Despite the success of the prior and post-WMONEX (Winter Monsoon Experiment) research in exploring the tropical-midlatitude interaction, the close interaction of cold surges with local weather systems and the planetary-scale circulation in east Asia, illustrated by the case study presented, provides another dimension of cold surge research.

Chen, T. C. and J. H. Yoon (2000). "Some remarks on the westward propagation of the monsoon depression." Tellus. Series A: Dynamic Meteorology and Oceanography 52A(5): 487-499.

Several westward propagation properties of the Indian monsoon depression were neglected by previous studies. They include: (1) the slower propagation speed of the depression depicted by a quasi-geostrophic model, (2) the initiation of the asymmetric secondary circulation with respect to the depression center, and (3) the absence of the depression perturbation in the upper troposphere. Some further insights into these neglected propagation properties of the depression are obtained from the streamfunction budget analysis with the ECMWF (European Centre for Medium Range Weather Forecasts) reanalysis data. (1) The inclusion of relative vorticity stretching, which is neglected in a quasi-geostrophic model, increases the depression's westward propagation speed. (2) Within the large-scale environment of the summer monsoon, the coupling of the east-west differentiation of the meridional absolute vorticity advection with the CISK mechanism is conductive to the initiation and development of the asymmetric secondary circulation associated with the depression. (3) The Tibetan high is formed by summertime global-scale stationary waves which are maintained by a Sverdrup balance. The positive streamfunction tendency induced by the upper-tropospheric vortex stretching over the monsoon region suppresses the development of the monsoon depression in the upper troposphere.

Chen, T.-C. and S.-P. Weng (1996). "Some effects of the intraseasonal oscillation on the equatorial waves over the western tropical Pacific-South China Sea region during the northern summer." Monthly Weather Review, Boston, MA 124(4): 751-756.

Previous studies have shown that the life cycle of the Asian summer monsoon is modulated by the 30-60-day oscillation; the arrival of the 30-60-day monsoon trough (ridge) at 15 degrees -20 degrees N intensifies (weakens) the monsoon flow over the South China Sea-western tropical Pacific region and, in turn, extends eastward (westward) the monsoon westerlies (trade easterlies) over this region. Since equatorial waves are important synoptic disturbances to the weather of this region, an effort was made in this study to explore the possible impact of the 30-60-day mode on the occurrence frequency and westward propagation of these waves. The major findings of this study are as follows: 1) the westward intrusion of trade easterlies during the break monsoon facilitates the occurrence and westward propagation of equatorial waves along trade easterlies in the southern flank of the North Pacific anticyclone, and 2) the eastward expansion of monsoon westerlies during the active monsoon varies relative to the activity of equatorial waves in a way opposite to the break monsoon condition. Since this is a pilot study, some future efforts are suggested.

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

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

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

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

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

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

Chen, T.-C., M.-C. Yen, et al. (2001). "Summer Upper-Level Vortex over the North Pacific." Bulletin of the American Meteorological Society 82(9): 1991-2006.

The midocean trough in the North Pacific may form a favorable environment for the genesis of some synoptic disturbances. In contrast, the North Pacific anticyclone may hinder the downward penetration of these disturbances into the lower troposphere and prevent the moisture supply to these disturbances from the lower troposphere. Because no thick clouds, rainfall, and destructive surface winds are associated with these disturbances to attract attention, they have not been analyzed or documented. Actually, the upper-level wind speed within these disturbances is sometimes as strong as tropical cyclones and has the possibility of causing air traffic hazards in the western subtropic Pacific. With infrared images of the Japanese Geostationary Meteorological Satellite and the NCEP-NCAR reanalysis data, 25 North Pacific disturbances were identified over six summers (1993-98). Two aspects of these disturbances were explored: spatial structure and basic dynamics. For their structure, the disturbances possess a well-organized vortex in the middle to upper troposphere with a descending dry/cold core encircled by the moist ascending air around the vortex periphery; the secondary circulation of the vortex is opposite to other types of synoptic disturbances. Since vorticity reaches maximum values along the midocean trough line, barotrophic instability is suggested as a likely genesis mechanism of the vortex. After the vortex is formed, the horizontal advection of total vorticity results in its westward propagation, while the secondary circulation hinders this movement. Along its westward moving course, close to East Asia, there is a reduction in vortex size and a tangential speed increase inversely proportional to the vortex size. Diminishing its horizontal convergence/descending motion by the upper-tropospheric East Asian high and the lower-tropospheric monsoon low, the vortex eventually dissipates along the East Asian coast.

Chen, T.-C., M.-C. Yen, et al. (1988). "Water vapor transport associated with the 30-50-day oscillation over the Asian monsoon regions during 1979 summer." Monthly Weather Review, Boston 116(10): 1983-2002.

In this study, the water vapor transport over the entire Asian monsoon region is studied by using the FGGE 3-b data of the European Centre for Medium Range Weather Forecasts (ECMWF) and the Geophysical Fluid Dynamics Laboratory (GFDL). An effort is made to explore the possible effect of the 30-50-day oscillation on water vapor transport. The empirical orthogonal function (EOF) analysis is applied to the potential and streamfunction of the vertically integrated water vapor transport over a region (25 degrees S-60 degrees N, 40 degrees E-130 degrees W). It is found that the water vapor transports over the Indian and East Asian monsoon regions are related to each other through their interactions with the eastward-propagating 30-50-day oscillation. Several occurrences follow the 30-50-day oscillation of the Indian monsoon westerlies in a coherent manner: the E-W shifting of the water vapor convergence center over the Asian monsoon regions; the N-S movement of the North Pacific convergence zone (NPCZ); and the merging of the water vapor flux transported by the Indian monsoon westerlies and the Pacific anticyclone trade winds over the South China Sea. The development of the East Asian monsoon is characterized by the N-S movement of water vapor fronts, such as the mei-yu and bai-u fronts, associated with the NPCZ. This study reveals that this N-S movement is caused by the eastward propagation of the 30-50-day mode. The EOF analysis is also applied to the global potential function of the water vapor transport between 45 degrees S and 45 degrees N over the entire FGGE year. It is suggested that the phase relationship between the annual cycle and the 30-50-day mode of the potential function of the water vapor transport can be used to explain the development of the large-scale environment for the Indian monsoon over its entire life cycle. It is also inferred, from the time lag between onsets of the Indian and East Asian monsoon, that the two monsoons may be induced by the same mechanism, namely, the interaction between the annual cycle and the 30-50-day low-frequency mode.

Chen, T.-C. and J.-H. Yoon (2000). "Some remarks on the westward propagation of the monsoon depression." Tellus Series A: Dynamic Meteorology and Oceanography, Stockholm, Sweden 52A(5): 487-499.

Several westward propagation properties of the Indian monsoon depression were neglected by previous studies. They include: (1) the slower propagation speed of the depression depicted by a quasi-geostrophic model, (2) the initiation of the asymmetric secondary circulation with respect to the depression center, and (3) the absence of the depression perturbation in the upper troposphere. Some further insights into these neglected propagation properties of the depression are obtained from the streamfunction budget analysis with the ECMWF (European Centre for Medium Range Weather Forecasts) reanalysis data. (1) The inclusion of relative vorticity stretching, which is neglected in a quasi-geostrophic model, increases the depression's westward propagation speed. (2) Within the large-scale environment of the summer monsoon, the coupling of the east-west differentiation of the meridional absolute vorticity advection with the CISK mechanism is conducive to the initiation and development of the asymmetric secondary circulation associated with the depression. (3) The Tibetan high is formed by summertime global-scale stationary waves which are maintained by a Sverdrup balance. The positive streamfunction tendency induced by the upper-tropospheric vortex stretching over the monsoon region suppresses the development of the monsoon depression in the upper troposphere.

Chen, X. A. and Y.-L. Chen (1995). "Development of low-level jets during TAMEX." Monthly Weather Review, Boston, MA 123(6): 1695-1719.

Detailed synoptic-scale map analysis and diagnosis for all six low-level jet (LLJ) cases that occurred during the Taiwan Area Mesoscale Experiment (TAMEX) were made to study the structure and the development of the LLJs. It was shown that the development of these LLJs was closely linked to the development of a lee trough to the east of the Tibetan Plateau. Seasonal change had a profound influence on the secondary circulation across the jet front system. Before the seasonal transition, the formation of a lee trough with closed isobars in low levels east of the Tibetan Plateau occurred as an upstream shortwave trough moved eastward with strengthening westerlies over the Tibetan Plateau in upper levels. After the development of the lee trough, the southwest flow appeared in the southeast quadrant of the lee trough. As the upstream trough moved farther easward, it merged with the lee trough, and the low-level southwesterly flow intensified. For most cases, a midlatitude deep trough was present to the north or northeast at this time; the northwesterlies behind the midlatitude trough brought in the cold air to the rear of the merged trough. The upper-level jet ahead of the merged trough strengthened. The secondary circulation across the jet front system was characterized by a thermally direct circulation across the baroclinic zone, with warm air rising within the southwest monsoon flow, cold air sinking in the postfrontal northeasterlies, and a weak thermally indirect circulation to the south. After the seasonal transition, the major baroclinic zone shifted northward, and the upper-level south Asian high pressure cell moved over the Tibetan Plateau. The Tibetan high dominated the upper-level circulations with easterlies along the southern China coast, preventing baroclinic disturbances from moving into southern China. At 1200 UTC 22 June 1987, an orographically induced lee trough formed in the lee side of the Tibetan Plateau. An LLJ was observed during 0000 UTC 23 June-0000 UTC 25 June 1987 over the southern China coast as a southwest vortex developed within the lee trough. The formation of the vortex was driven by latent heat release in a barotropic environment. the secondary circulation associated with the LLJ was charcterized by a rising motion northwest of the LLJ axis and a broad sinking motion to the south.

Chen, Y. and B. Zhu (1985). "Synoptic features of rain season in Yunnan Province before outbreak of tropical monsoon." Scientia Atmospherica Sinica, Peking 9(1): 101-106.

A special weather phenomenon, the early rain in Yunnan Province, which takes place in the lee of the Tibetan Plateau, is studied and the synoptic system causing the sustained rain and its seasonally varying features are discussed. By diagnostic analysis of static energy, it is found that there are discrepancies between the early rain and the rainy season that begins with the arrival of the Indian monsoon, and there are some correlations between the onset of the early raining and the first storm in the Bay of Bengal. The relations of the early rain to seasonal variations of general circulation in East Asia are also discussed.

Chen, Y.-L. and N. B. F. Hui (1992). "Analysis of a relatively dry front during the Taiwan Area Mesoscale Experiment." Monthly Weather Review, Boston, MA 120(11): 2442-2468.

The evolution of a relatively dry front during the early-summer rainy season of Taiwan is analyzed. Because of the synoptic subsidence associated with a subtropical high pressure cell over the northern South China Sea, prefrontal soundings over the Taiwan area exhibited a shallow, warm, moist layer in the lowest levels, capped by an inversion with extremely dry air aloft. Over the Taiwan area, the southwest flow ahead of the surface front was more than 10 m s super(-) super(1) at the 850-mb level. It interacted with the central mountain range, resulting in the windward ridge, leeside trough. Downstream of the blocked region, strong southwesterly winds ( similar to 15 m s super(-) super(1) ) developed in the lowest levels along the northwest coast, where the flow deflected by the mountain barrier merged with the undeflected southwest monsoon flow. The hilly terrain along the southeastern China coast retarded the cold air behind the surface front. The cold air was then ducted around the southeastern China coast. At the 850-mb level, a weak short-wave trough was embedded in the prefrontal monsoon flow. It moved off the southeastern China coast before cold northeasterlies arrived at the surface. It deepened in the lee side of the highlands along the southeastern China coast, with significant low-level warming and drying. Aircraft observations of the leading edge of the shallow front revealed that a warm, moist tongue was ahead of the wind-shift line, where the winds shifted from northwesterlies to northeasterlies. Behind the leading edge, the air had a uniform equivalent potential temperature below 700 m. The stable, cold air was found 50 km north of the leading edge, with a warm, moist tongue ahead of it. East of Taiwan, the shallow, cold air behind the front appeared to be warmer than its western counterpart, with a well-mixed layer below 650 m. Since the prefrontal soundings over the Taiwan area were dry with a level of free convection (LFC) above the 800-mb level, local lifting by a shallow front was apparently not sufficient to initiate deep convection leading to heavy precipitation.

Cheung, K. K. W. and R. L. Elsberry (2002). "Tropical Cyclone Formations over the Western North Pacific in the Navy Operational Global Atmospheric Prediction System Forecasts." Weather and Forecasting 17(4): 800-820.

A set of criteria is developed to identify tropical cyclone (TC) formations in the Navy Operational Global Atmospheric Prediction System (NOGAPS) analyses and forecast fields. Then the NOGAPS forecasts of TC formations from 1997 to 1999 are verified relative to a formation time defined to be the first warning issued by the Joint Typhoon Warning Center. During these three years, the spatial distributions of TC formations were strongly affected by an El Nino-Southern Oscillation event. The successful NOGAPS predictions of formation within a maximum separation threshold of 4 ' latitude are about 70%-80% for 24-h forecasts, and drop to about 20%-30% for 120-h forecasts. The success rate is higher for formations in the South China Sea and between 160 'E and 180 ' but is generally lower between 120 ' and 160 'E. The composite 850-hPa large-scale flow for the formations between 120 ' and 160 'E is similar to a monsoon confluence region with marked cross-equatorial flow. Therefore, it is concluded that the skill of NOGAPS in predicting TC formations with a monsoon confluence region pattern is lower than for other formation patterns. The number of false alarms (FAs) in NOGAPS is also examined. All the vortices in the 24-120-h forecasts that satisfy the above-defined criteria of a TC formation are identified and then compared with the formations (or nonformations) in the verifying analyses. The number of FAs is relatively low in the 24-h forecasts, increases through the 48-h forecasts, and then is about the same in the subsequent forecast times up to 120 h. Both the longitudinal distributions of the FAs during the three years and the meridional variations of the FA locations within a season are generally similar to the observed TC formations. Several large-scale features are compared for the successful and failed predictions during the 3-yr period. In general, the failed predictions have a slightly larger westerly vertical wind shear south of the TC formation location than in the successful predictions. The predicted relative humidity of the failed predictions is lower than in the successful formation forecasts. Thus, predicting too large a vertical wind shear and too dry an environment may be partially responsible for the failed cases. To further diagnose the failed predictions, various terms contributing to the angular momentum tendency are examined.

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

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

Chistyakova, Y., R. Mizkiddorzh, et al. (1992). "On a possibility to forecast the summer weather in Mongolia taking into account the large-scale circulation of the atmosphere." Trudy ordena Lenina Gidrometeorologicheskovo nauchno issledova telskovo tsentra [Proceedings of Hydrometeorological Research Center holding Order of Lenin.], Saint Petersburg, Russia 319: 56-64.

The monsoon index introduced by D. A. Ped' is defined by the pressure difference between Siberian maximum and Aleutian minimum (winter) and between south Asian low and Pacific high (summer). Effects of the monsoon on stratospheric circulation changes and on the air temperature and precipitation anomalies in Mongolia are studied using the anomality index along with indices k sub(1) and v characterizing frequencies of negative and positive anomalies of temperature and precipitation. Namely, k sub(1) is the averaged difference of sums of squared ratios of positive and negative temperature anomalies to the corresponding variances, while v is defined by the ratio of difference between the numbers of sites with excessive and deficient precipitation (i.e. with precipitation amounts exceeding 120 and less than 80% of the climatic normal) to the total number of the stations. The 1960-1986 data on temperature and precipitation at 25 and 60 stations in Mongolia, respectively, are used. Moving 5-year average indices are examined for May to September; it is found that v greater than or equal to 0.4 (large anomaly) is the most frequent in May and August (55 and 59%, respectively). Synchronous connections are well-defined between the monsoon index and the precipitation anomalies, while the temperature anomalies are found to be asynchronously connected with the index: k sub(1) in July is correlated with the monsoon index in April in 73% of the area (correlation rates up to 0.64). Less pronounced inverse relationship is found for precipitation: in 54% of the area, intense monsoon in April involves dry July (correlation rates up to 0.42); the result is confirmed by the data on wheat productivity in the central part of Mongolia.

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.

Chowdhury, A., V. P. Abhyankar, et al. (1981). "Solar activity as a potential factor for foreshadowing drought in Indian summer monsoon regime." Mausam, New Delhi 32(3): 277-280.

An attempt was made to determine the influence of solar activity upon drought incidence in India. Rainfall for 100 years (1875-1974) in northwest and peninsular India were analyzed with regard to sun-spot numbers and Baur's solar index, and their distribution during drought years was determined. Frequency of drought per cycle of solar activity was obtained. The association between drought and maximum-minimum spottedness was tested by the chi-square technique. A correlation was computed among sun spots, Baur's index, and rainfall during different phases of solar activity. The results reveal that, on an average, drought occurs once in a solar cycle. Occurrence of maxima or minima had no relationship to the drought, which was found to occur earlier as well as later than either of the epochs. Correlation analysis revealed that, for the peninsula, sun-spot numbers and values during the middle of the waxing phase were significant. Baur's index bears significant correlation with northwest Indian rainfall. Its value during the waxing phase, as during the middle of the waxing phase, is also significantly correlated with northwest Indian rainfall. The index was significant for peninsula rainfall during the middle of the waxing phase.

Chowdhury, A., M. M. Dandekar, et al. (1989). "Variability in drought incidence over India: a statistical approach." Mausam, New Delhi 40(2): 207-214.

Based on the monsoon rainfall for 113 yr (1875-1987), an attempt has been made to quantify drought for the country as a whole and identify drought years by developing a drought index. For this purpose, the total area of India receiving monsoon rainfall <75% of the normal was obtained for each of the 113 yr, and the mean drought-affected area and its standard deviation were worked out. The difference between area affected by drought in any year and the 113-yr mean drought area divided by the standard deviation was defined as the drought index. The time interval between successive drought years has been subjected to statistical analysis, and the distribution determined and tested for randomness. The series of drought years was also subjected to return period analysis. Within the analyzed time frame, 1918 is found to be the worst drought in India. It is observed that India can sometimes even experience spells of three successive years of drought of varying intensity and extent. The time interval between successive drought years can be approximately described by Poisson's distribution.

Chowdhury, A. and G. S. Sarwade (1984). "Drought prediction in India from radiation parameters." Mausam, New Delhi 35(3): 345-348.

Monthly values of total global (G) and diffuse (D) radiation from Jan. to May for all available stations during the period 1961-1979, were used in this study. Drought, for this purpose, is defined as a situation when >20% of the area of the country has rainfall deficiency of >25% of the seasonal (monsoon) normal. Departures from the normal value of total global radiation have been plotted, monthly and for the winter and premonsoon seasons, and analyzed to determine whether the spatial distribution pattern bears any relationship with drought occurrence in the succeeding monsoon season. Cumulative totals of G and cumulative departures for individual stations have also been plotted and examined in relation to drought. capital sigma (D-D)/(G-G) has been obtained for the winter and monsoon months for different stations as an index where the bar denotes normal values, and there is an attempt to associate them with drought incidence in India. Short-wave radiation values at approximately the same meridian, but at nearly two extremities of the country, Trivandrum and Delhi, have been analyzed separately. Heat content over the country has assumed a difference between the radiation values at these stations. These values were obtained from Jan. to May and suitably analyzed with regard to the drought situations in India.

Chu, P.-S. and D. N. Sikdar (1983). "Characteristics of sea level pressure and surface temperature variations during winter MONEX, Dec. 1978." Meteorological Society of Japan, Tokyo, Journal 61(6): 717-726.

Interdiurnal variations of sea level pressure and surface temperature are studied by using the WMONEX/FGGE level 2-b data set for the region bounded by 30 degrees N-10 degrees S and 100-130 degrees E during Dec. 1978. Results of spatial cross-correlation patterns indicate an eastward phase propagation of pressure and temperature maxima with speed similar to 10-long./day over Southeast China and the adjacent ocean, apparently associated with the traveling midlatitude disturbances. In the meridional direction, pressure oscillations in the midlatitudes are highly correlated with those over Indochina for three consecutive days, but not with those over the bulk of the South China Sea. This difference in correlations indicates a change in the characteristics of the air mass as it traverses land and sea. Temperature analysis implies the influence of heat transfer between the ocean and atmosphere to the areas south of 15 degrees N. An eigenvector analysis is applied to both the pressure and temperature series. The first eigenmode resembles the pattern associated with the East Asia local Hadley circulation. The second eigenvector represents wintertime anticyclone and cyclone patterns over Southeast China and its adjoining ocean and, thus, the cold surge events. Time series of the first two eigenmodes are discussed in terms of the winter monsoon circulation during this period.

Daggupaty, S. M. and D. R. Sikka (1977). "On the vorticity budget and vertical velocity distribution associated with the life cycle of a monsoon depression." Journal of the Atmospheric Sciences, Boston 34(5): 773-792.

The results obtained from a diagnostic study of a monsoon depression that formed in the northern part of the Bay of Bengal are discussed. The depression intensified as it progressed westward across India, at a speed of about 5 degrees long./day. The computed vertical velocity agrees with the observed asymmetric distribution of rainfall around the depression. The presence of a low level of nondivergence (i.e., around 850 mb) is found to have a significant role in the dynamics of the monsoon depression. The important result of the computed vorticity budget over the period of the intensification of the depression is the detection of a middle and upper tropospheric cyclonic vorticity depletion because of large-scale dynamics in the western sector of the depression. This result is unexpected because of the fact that the depression's observed cyclonic vorticity increases with westward progress, not only in the lower troposphere, but also in the middle and upper troposphere. It is shown that the presence of deep convective cloud activity in the western sector provides the necessary process to compensate the negative vorticity tendency in the middle and upper troposphere. Through a simple parameterization, it is qualitatively shown that the transport of subgrid-scale vorticity by deep convective clouds in the western sector is significant. This mechanism of vertical transport of extremely rich boundary layer cyclonic vorticity by deep convective clouds is essential for the intensification and westward movement of the monsoon depression.

Dashko, N. A., S. M. Varlamov, et al. (1997). "Atmospheric centers of action in the Asian-Pacific region and summer weather features at the coasts of the Sea of Japan and Sea of Okhotsk." Meteorologiya i Gidrologiya [Meteorology and Hydrology.], Moscow, Russia 9: 14-24.

Synoptic features of atmospheric centers of action (CA) in the Asian-Pacific Region are statistically studied, with main attention paid to anticyclogenesis over the Sea of Okhotsk. The data under consideration are weather and height charts (1949-1996), weather observations (1949-1990), and data about intensity and location of CA (1900-1996). Time evolution of the latter is characterized by pressure monthly linear trends in the centers of North-Pacific maximum (increase in April to August, up to 0.45 mb/10 years) and Siberian maximum (decrease in November to March, to -1.2 mb/10 years). On the background of the trends, waves of the main CA activity occur. Over the Sea of Okhotsk, at the periphery of North-Pacific maximum, a closed cold and shallow high is formed, which is the most frequently observed in June (50%). In the surface pressure field of May to July, 7 typical situations are revealed, 5 of which having anticyclonic circulation. The most frequently (84%) this type of circulation remains for 10 days and more. The summer monsoon airmass, warm and moist, is formed in the North-Pacific maximum area. This airmass is cooling down and reaching saturation over the cold Sea of Okhotsk. This air affects strongly weather of the coastal areas. Correlation rates for air temperature at the coastal stations and in the gridpoints in the Sea of Okhotsk reach 0.5-0.8. Pressure over the sea and precipitation at the Primorski Krai coast and Sakhalin Island are also correlated (r of 0.4 to 0.5 and of -0.4 to -0.6, respectively).

Davidson, N. E. (1995). "Vorticity budget for AMEX. Part II: Simulations of monsoon onset, midtropospheric lows, and tropical cyclone behavior." Monthly Weather Review, Boston, MA 123(6): 1636-1659.

Diagnostics from the observational dataset of the Australian Monsoon Experiment (AMEX) have revealed two interesting characteristics of convective systems over the Australian Tropics (Part I of this study). The first is a midlevel convergence maximum in situations of disorganized convections, which implies weak low-level and strong upper-level convective heating. The second is the presence of large apparent vorticity sources during deep convective and stratiform events. It is suggested that these characteristics are related to the ascent and descent motions in tropical cloud systems and to the way in which they redistribute mass and the background vorticity. To investigate the importance of these features of convection on tropical prediction, a representation of the observed thermodynamic and kinematic effects of clouds has been implemented in the Bureau of Meteorology Research Centre's tropical limited-area model. To represent the observed structure of convective heating in numerical simulation experiments, an analytic heating function is constructed that is similar to the observed heating profile. Satellite cloud imagery is then used to trigger the function in space and time during the model integration. In this way the importance of the convective processes can be assessed, without the uncertainties of incorrect triggering of the parameterization. To represent the observed structure of convective heating numerical prediction experiments, the Kuo heating profile is modified to reflect the (AMEX) observed profile, with weak low-level heating. To parameterize the kinematic effects, a potential function is introduced. Vorticity tendencies due to clouds are represented by the Laplacian of the function, and the momentum tendencies by the spatial derivatives. Vorticity tendencies are specified according to the observed structure of apparent sources and are dependent on the level of maximum convergence and the ambient vorticity and divergence profiles. The representation of convection, including both thermodynamic and kinematic effects, has been run in a number of simulations of AMEX weather events. It is shown that, in a limited number of events, realistic forecasts of monsoon onset, midtropospheric lows, and tropical cyclogenesis can be obtained. For tropical cyclogenesis, it is shown that upper-level convective heating produces the required midlevel convergence and eventually a midtropospheric circulation. The parameterized apparent vorticity sources then act to spin down the midlevels and spin up the upper and lower levels. This, together with the resultant enhanced boundary layer convergence, is sufficient to intensify the low-level circulation without the need for large low-level convective heating. Indeed, simulations with convective heating, and no representation of apparent vorticity sources, cannot accurately reproduce the observed four-dimensional structure of the developing tropical cyclone.

Davidson, N. E. (1995). "Vorticity budget for AMEX. Part I: Diagnostics." Monthly Weather Review, Boston, MA 123(6): 1620-1635.

Six-hourly analyses based on the special observational dataset from the Australian Monsoon Experiment are used to derive vorticity budget diagnostics for a number of tropical weather situations. The quality of the analyses is demonstrated by observation fitting statistics, comparison of digital satellite cloud imagery with diagnosed vertical motion, and by comparison of derived quantities with those obtained directly from the observations using line integral calculations. For the mean of the entire experimental period, balance generally exists between stretching and horizontal advection, with some contribution from an apparent vorticity source at upper levels. The individual-day behavior, however, is often quite different. Three categories are evident: 1) For weak, low-level cyclonic flows at the time of maximum convection (disorganized, deep convection), an apparent source of cyclonic vorticity is evident at low and high levels, and a sink is indicated through midlevels. These situations are characterized by a midlevel convergence maximum and a related cyclonic vorticity maximum. 2) For strong, low-level vorticity regimes (circulation systems with organized convection), an apparent sink of vorticity is evident everywhere below the convective outflow level, with a source above. These situations are characterized by deep convergence and a low level of maximum vorticity. 3) The third category, which seems to be associated with mostly stratiform regimes, is similar to 1), but a source is diagnosed at mid- to high levels (possibly associated with the stratiform cloud deck) with a sink farther aloft. The author postulates that the vertical structure of apparent vorticity sources is determined by the ascent and descent motions of the dominant cloud forms, which redistribute the background vorticity, and by enhanced boundary layer convergence as circulation systems spin up. The implications of the (a) midlevel convergence maximum and (b) apparent vorticity sources to the understanding and prediction of monsoon onset, midtropospheric cyclones, and tropical cyclone behavior are discussed. In a companion paper, a representation of the apparent heat and vorticity sources is implemented in a numerical model and used in simulations of the above weather phenomenon.

Davidson, N. E. and H. H. Hendon (1989). "Downstream development in the Southern Hemisphere monsoon during FGGE WMONEX." Monthly Weather Review, Boston 117(7): 1458-1470.

Evidence is presented of a downstream development mechanism operating across the entire longitudinal span of the 1978-1979 Southern Hemisphere monsoon. Observationally it is seen as progressive cyclonic and anticyclonic vorticity increases that develop eastward in the monsoon trough at a speed of similar to 5 m sec super(-) super(1) . The process results in many tropical cyclone and tropical depression formations over northern Australia and the South Pacific. It is shown that the downstream development process is generally consistent with linearized barotropic dynamics, and that the Southern Hemisphere monsoon, because of an intrinsic westerly basic state, is a particularly suitable region for downstream events. Some apparent contradictions in previous observational studies can be rationalized by the theory. The interactions between the regional components of the monsoon (Indonesian, Australian, and South Pacific sectors) can also be better understood. It is suggested that the process has implications for other features of the monsoon circulation, namely onset and 40-50-day events.

Davidson, N. E. and G. J. Holland (1987). "Diagnostic analysis of two intense monsoon depressions over Australia." Monthly Weather Review, Boston 115(2): 380-392.

Analyses of mean sea level pressure, wind, temperature, and dew point are used to study the life cycles of two intense, heavy-rain-producing monsoon depressions over northern Australia. Two aspects are considered: 1) the large-scale forcing, using both synoptic flow field changes and angular momentum budgets; and 2) the role of convective and stratiform clouds, using kinematic and thermodynamic budgets. For each situation, the Northern Hemisphere circulation becomes favorable, well prior to genesis. The short-term trigger for development is the strengthening of the Southern Hemisphere subtropical ridge at the surface and an amplifying upper level trough and subtropical jetstreak to the southwest of the formation point. The outer region structure of these monsoon depressions is remarkably similar to that of a tropical cyclone, even though the systems develop over land. During development, maximum convective heating occurs at middle levels and within a region of already high cyclonic vorticity. Evidence suggests that the cloud population is comprised mostly of deep cumulonimbus clouds, middle-level stratiform clouds, and shallow cumulus. The physical significance of these findings is discussed.

Davidson, N. E. and A. Kumar (1990). "Numerical simulation of the development of AMEX tropical cyclone Irma." Monthly Weather Review, Boston, MA 118(10): 2001-2019.

High resolution observational data from the Australian Monsoon Experiment have been used to verify simulations of the development of tropical cyclone Irma. From a small amplitude, prehurricane cloud cluster, the FSU high resolution regional prediction model quite skillfully simulates the temporal and spatial structure changes during development. The results are, however, sensitive to the initial windfield and somewhat sensitive to both the initial moisture field and the imposed boundary conditions. Temporal changes in the symmetric and asymmetric structure of the observed and simulated disturbances are compared. Apart from other well-documented necessary conditions, changes in the storm's vertical structure, and the development of horizontal asymmetries appear to be crucial features of the simulated development. The associated physical processes are discussed. Deficiencies in the simulation are lack of diurnal modulation of the vertical motion field, larger than diagnosed values of vertical motion over the genesis area, and an upper level flow that is too divergent and anticyclonic. We speculate that more accurate representation of diurnal effects, and a parameterization of momentum transports by cumulus clouds will reduce these deficiencies.

Davidson, N. E., J. L. McBride, et al. (1983). "Onset of the Australian monsoon during winter MONEX: synoptic aspects." Monthly Weather Review, Boston 111(3): 496-516.

A case study is presented of the onset of the Southern Hemisphere summer monsoon at longitudes near Australia during Dec. 1978. The numerical analyses comprising this case study are used in conjunction with station data and operational manually derived analyses for other years to investigate 1) the ease of definition of monsoon onset; 2) the three-dimensional structure of the troposphere during an active monsoon situation; and 3) the flow changes preceding and during the transition from a period of suppressed to a period of enhanced cumulonimbus activity over tropical Australia. A well-defined onset occurs in six of the seven years considered. Onset, defined as a satellite-observed, large-scale increase in tropical convection, is consistent with that determined by the wind criterion of Troup (1961). In 1978, onset occurs in two stages: an increase in convergence, followed by an increase in convection. The monsoon cloudiness exists entirely in the region of low-level westerly wind. The convergence extends through a deep layer from the surface to 400 mb and exists in the upward branch of two linked Hadley cells, one from each of the Northern and Southern Hemispheres. Observations of the flow changes prior to onset lead to the hypothesis that the trigger mechanism lies in the Southern Hemisphere subtropics. It is conjectured that the seasonal buildup of planetary-scale land-sea temperature gradients has reached a critical stage such that the troposphere is in a state of readiness for the monsoon. Before the onset can take place, however, it must wait for the Southern Hemisphere midlatitude synoptic systems to be in such a configuration that low-level trade wind easterlies are prevalent across the Australian continent. Evidence is discussed in favor of various alternative triggering mechanisms such as the influence of a Northern Hemisphere cold surge in the South China Sea and the westward propagation of equatorial westerlies from the Pacific Ocean near the international date line.

Davidson, N. E., J. L. McBride, et al. (1984). "Divergent circulations during the onset of the 1978-79 Australian monsoon." Monthly Weather Review, Boston 112(9): 1684-1696.

Large-scale numerical analyses of divergence and the divergent component of wind are examined at two levels in the lower and upper troposphere. The synoptic sequence studied includes the onset of the Southern Hemisphere summer monsoon. Comparison with satellite-observed cloudiness leads to the conclusion that the analyzed patterns of divergence contain synoptically realistic meteorological information. There seems to be virtually no information, however, in the day-to-day changes in magnitude of analyzed divergence in the lower troposphere and only a weak signal in the upper troposphere. The divergent wind analyses reveal the intertropical convergence zone (ITCZ) to be a readily identifiable feature on individual days and its location to be both vertically consistent and coincident with the satellite-observed cloud. Two days prior to monsoon onset, the analyzed ITCZ moves poleward by 8 degrees lat. Monsoon convection exists at the intersection of Northern and Southern Hemisphere Hadley cells; it is well removed from the upward branch of any E-W Walker circulations in this situation. The concept of a divergent surge is introduced to denote vertically consistent divergent circulations extending over distances >20 degrees lat. This concept is shown to be useful in the physical interpretation of the role of the Southern Hemisphere subtropics in the triggering of monsoon onset. Use of the concept is also helpful in relating the day-to-day changes in tropical convection to simultaneous changes in location and intensity of (mean sea level) subtropical high-pressure cells in both hemispheres. Solutions for the divergent component of wind calculated over a limited domain are compared with solutions calculated over a sphere.

De, U. S. and A. B. Mazumdar (1999). "Principal components analysis of rainfall and associated synoptic models of the southwest monsoon over India." Theoretical and Applied Climatology, Vienna, Austria 64(3-4): 213-228.

The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared utilising all available upper air data (1977-1986) for each category of the SW monsoon epochs identified by the PCA. These sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal components (PCs). A well defined east-west oriented trough system, extending from about 28 degrees N Latitude/65 degrees E Longitude to 20 degrees N Latitude /90 degrees E Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features, such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric anticyclones to the south. The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition, synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner by such PCA.

Degtyarev, A. I. (1999). "Influence of the Indian summer monsoon on the formation of tropical cyclones over Southeast Asia." Russian Meteorology and Hydrology, New York, NY 7: 38-42.

The ECMWF objective analysis data on the variability of kinetic energy in the tropical atmosphere over the Indian Ocean and Southeast Asia water area in 1995 and 1996 are analyzed. The intraseasonal variability of the Indian summer monsoon is found. Tropical cyclogenesis over the South China Sea and the Philippine Islands is shown to occur more often in the active phase of the Indian monsoon than during its breaks. It turned out that the westerly wind intensification, an active monsoon phase, leads to a deepening of the monsoon trough and creates favorable conditions for the formation of tropical cyclones over the study region.

Dengler, K. and R. K. Smith (1998). "A monsoon depression over northwestern Australia. Part II: A numerical model study." Australian Meteorological Magazine, Canberra, Australia 47(2): 135-144.

A numerical shallow-water model is used to investigate dynamical aspects of the evolution of an initial weak and broad vortex circulation in the absence of a basic flow. The initial vortex lies partly over land and is centred over the coast which is straight and runs from southwest to northeast. The situation is relevant to the case study of the development of a monsoon depression near the northwestern coast of Australia presented in Part I. The model incorporates a modified form of the convective parametrisation scheme developed by Ooyama. The modifications were found to be necessary when the cyclonic circulation has its centre in the proximity of land. On an f-plane the initial vortex intensifies to a strength comparable to that of the observed monsoon depression and moves eastwards over the land. The eastward drift is caused by asymmetries in the convection which are a result of the land-sea distribution. On a beta-plane the motion is dominated by the flow associated with the beta-induced vorticity asymmetries and the vortex moves southwestwards and further inland. Accordingly, its maximum intensity is less than that on the f-plane. On a beta-plane in the absence of land, the vortex attains the strength of an intense tropical cyclone with maximum winds of 48 m s super(-) super(1) and drifts towards the southwest.

Desai, B. N. (1979). "Role of mountains in the development of the Indian summer monsoon circulation and the associated weather." Mausam, New Delhi 30(4): 463-468.

Special features of the Indian summer monsoon mentioned by Hahn and Manabe (1975) in their model simulated with mountains are discussed with reference to the model for surface layers given by Banerji (1930), taking into account the effect of mountain ranges on the airflow and configuration of isobars on the basis of thermodynamic and hydrodynamic considerations and the author's 50 yr of experience with weather observation. The lower monsoon circulation and the upper tropospheric circulation developed independently. The barriers west of the east coast of Africa are responsible for the deflection of the southeast trades north to northeastward across the Equator under the influence of the heat low (whose location is influenced by barriers) over south Pakistan and the monsoon trough circulation at levels up to about 600 mb, which is due to the influence of the mountains on the Indian subcontinent. The westerly jet is not a part of the monsoon circulation, and its shift from the south to the north of Tibet does not necessarily coincide with the onset of the monsoon. There does not appear to be any cause-and-effect relation between the development and strength of the easterly jet and the onset and performance of the monsoon in terms of rainfall. The low-level jet is embedded in the monsoon current and is noticed even to the east of Madagascar and in the western Indian Ocean and the adjoining eastern coastal areas of Africa (Findlater, 1969). It does not appear to develop as a result of upwelling of water off the Somalia coast, which has led to its being named the Somalia jet (Bunker, 1965). The seasonal rainfall can be understood on the basis of the influence of mountains, although the proximity of the tracks followed by the depressions while moving west to northwestward from the north Bay of Bengal increases the amount of rainfall. Small amounts of rainfall northwest of the subcontinent appear to be due to the absence of barriers over the coast, extending from Karachi (Pakistan) to Veraval in Gujarat (India) and to the presence of low-level inversions caused by the spreading of relatively warmer, drier air between about 1 and 3 km from the Baluchistan plateau side over the lower, cool moist monsoon air. There is no ITCZ over the monsoon trough area up to about 600 mb once the monsoon is established. Breaks in monsoon rain appear to be associated with the high-pressure anomalies over the monsoon trough area and the adjoining area to the south, which prevent the Southern Hemispheric air from being drawn to the west coast of India.

Dethof, A., A. O'Neill, et al. (1999). "A mechanism for moistening the lower stratosphere involving the Asian summer monsoon." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 125(556, Pt. B): 1079-1106.

This study employs European Centre for Medium-Range Weather Forecasts (ECMWF) re-analysis data and the contour advection technique to investigate the water vapour distribution in the upper troposphere and lower stratosphere. Water vapour is the primary greenhouse gas and understanding the processes which determine its distribution and transport is crucial. Of special interest is the exchange of water vapour across the tropopause. This study considers how the Asian summer monsoon affects the moisture budget of the upper troposphere and lower stratosphere. The region of the Asian summer monsoon is identified as a significant moisture source for the upper troposphere outside the deep tropics. Monsoon convection moistens the region of the upper-level monsoon anticyclone which is located close to the dynamical tropopause, where isentropes cross from the troposphere into the stratosphere. An isentropic analysis reveals that transport from the troposphere into the stratosphere in this region is normally prevented by the strong potential-vorticity gradients around the tropopause. However, midlatitude synoptic disturbances occasionally interact with the monsoon anticyclone and pull filaments of tropospheric air from its northern flank. These filaments, characterized by high values of humidity and low values of potential vorticity, can extend far north and transport moisture irreversibly into the Northern Hemisphere lower stratosphere. MOZAIC (Measurement of OZone by Airbus In-service airCraft) data are used as an independent data source to validate the results obtained from the ECMWF analyses.

Dhar, O. N., B. N. Mandal, et al. (1984). "Rainfall distribution over India during the monsoon months in the absence of depressions and cyclonic storms." Mausam, New Delhi 35(3): 309-314.

It is well known that monsoon depressions and cyclonic storms play an important role in the distribution of rainfall over India. Their absence from the Indian area during any month of the monsoon season is considered to be responsible for causing deficient rainfall and consequent drought conditions. It is, therefore, of interest to know to what extent the absence of these synoptic systems causes deficient rainfall during the individual monsoon months. This aspect has been examined by computing the average rainfall of the different meteorological subdivisions of the Indian plains north of 15 degrees N lat. for monsoon months that were free from depressions and cyclonic storms. There have been 25, 13, 7, and 4 occasions of June, July, Aug., and Sept., respectively, when no depressions or cyclonic storms moved through the Indian land area during the period 1891-1980. This study has shown that 1) of the four monsoon months, the Sept. month is worst affected by the absence of these disturbances, and 2) in the case of other monsoon months of June, July and Aug., rainfall can be abnormally deficient depending upon the presence of any of the following meteorological situations: late arrival and subsequent weak monsoon conditions over the country, the axis of monsoon trough remaining shifted to the north of its normal position, and nonoccurrence of low pressure areas (or land lows) across the country. Rainfall over the country can be normal or even above normal in spite of the absence of these disturbances if meteorological situations like the above are not present. This study, therefore, shows that the absence of monsoon depressions and cyclonic storms is not the main factor that causes deficient rainfall and consequent drought conditions in India.

Dhar, O. N. and S. Nandargi (1998). "Rainfall magnitudes that have not been exceeded in India." Weather, Bracknell, England 53(5): 145-151.

India receives heavy or very heavy rainfall during the pre-monsoon, monsoon and post-monsoon seasons, associated with tropical weather systems such as storms and depressions. Using data from 1875 to 1990, an attempt has been made here to find out all stations that have recorded heavy rainfall of the order of 50 cm or more during an observation day. An attempt has also been made to determine the spatial distribution of these stations in the country and to study their broad characteristics. In so doing we give a brief resume of the network of rainfall stations in India from its inception to the present day. We then review the present network and data used for this study and present our findings. Highest observed one-day rainfall greater than or equal to 50 cm, spatial distribution of stations having recorded at least 50 cm in one day, some broad characteristics of stations having recorded 50 cm or more in an observation-day, and rainfall magnitudes not yet exceeded are related in this article.

Dhar, O. N. and S. Nandargi (1999). "Role of low pressure areas in the absence of tropical disturbances during monsoon months in India." International Journal of Climatology, Chichester, UK 19(10): 1153-1159.

In this study an effort has been made to find out the contribution of low pressure areas (or lows) towards the rainfall of northern and central India during the monsoon months of June to September in the absence of more intense cyclonic disturbances such as depressions, deep depressions and cyclonic storms. 15 years of data from 1983 to 1997 has been used to study this aspect. This study has shown that the occurrence of moderate to heavy rainfall mainly depends upon their frequency, life span, track followed and origin of these disturbances provided there are no inhibiting meteorological factors like `break' monsoon situations.

Diem, M. (1977). "Widespread heavy rainfall in the Kalahari Desert." Meteorologische Rundschau, Berlin 30(5): 138-144.

After 18 mo of drought, a widespread heavy rainfall occurred in the Kalahari Desert. The rainfall covered an area of 1200 x 675 km, and excluded local origin. Evaluation of the meteorological facts shows there was an invasion of cold air behind a low pressure area passing over southern Africa. The cold air flowed from southeast to northwest and north of 30 degrees S lat. and could be identified up to the 500-mb surface. The amount of the 3-day rainfall was equal to the monthly mean in South Africa, and reached the 3-4-time value in Botswana and Southwest Africa. Because of Schulze, the authors assume it was an early invasion of monsoon from the Indian Ocean.

Dilley, M. (1996). "Synoptic controls on precipitation in the valley of Oaxaca, Mexico." International Journal of Climatology, Chichester, UK 16(9): 1019-1031.

The valley of Oaxaca is an important agricultural centre in the highlands of southern Mexico. Precipitation is a major control on rain-fed agriculture. Daily, monthly, and annual precipitation in the valley of Oaxaca are linked synoptically to distinct meso- and large-scale patterns of atmospheric pressure and temperature. During the summer rainy season, daily precipitation in the valley coincides with lower atmospheric pressures over Mexico. Anomalous lows increase convergence and draw maritime air landward. From June through to September, monthly average 850 hPa level temperatures in the Mexico-USA border region are consistently higher during the valley's wettest years compared with dry years. This link with atmospheric temperatures in the border region suggests that precipitation in the valley of Oaxaca is affected by variations in the Mexico monsoon, a tongue of maritime air that is drawn up the Mexican west coast and into the south-west USA during summer. Precipitation in the valley of Oaxaca also varies according to the frequency and position of tropical storms and hurricanes in the Gulf of Mexico and Pacific Ocean. Significant correlations between precipitation in the valley and storm frequency occur during August and September. Finally, El Nino-Southern Oscillation (ENSO) warm events are associated with dry conditions in the valley owing to a southward displacement of the Inter Tropical Convergence Zone (ITCZ) during the low phase of the Southern Oscillation and diminished storm frequency in the Gulf of Mexico.

Ding, Y.-H. and E. R. Reiter (1983). "Large-scale hemispheric teleconnections with frequency of tropical cyclone formation over the Northwest Pacific and North Atlantic oceans." Archives for Meteorology, Geophysics, and Bioclimatology, Ser A, Meteorology and Geophysics, Vienna 32(4): 311-337.

Large-scale circulation features during months with many and with few tropical cyclones revealed the following conditions. 1) With many typhoons in the Northwest Pacific, a well-defined intertropical convergence zone (ITCZ) extended eastward to 160 degrees E and was displaced to 20 degrees N. At 200 mb, an extensive anomalous anticyclonic circulation prevailed over the western and central Pacific. The circulation at 500 mb over Tibet was often characterized by an upper trough or a low-pressure region. Conditions characteristic of a break in the monsoon prevailed in India. The monsoon trough at 500 mb and at the surface over the Indian peninsula was relatively weak and was accompanied by higher than normal rainfall in the northern part of India and lower than normal rainfall over the peninsula. The polar vortex tended to be weak and moved away from the North Pacific sector. Abnormally warm water was observed over the central and eastern Pacific, and abnormally cold water was seen over the western Pacific in summer as well as in the preceding spring. Sea surface temperatures (SST) in the region of the Kuroshio Current and in the latitude belt 30-40 degrees N were also abnormally warm. 2) Over the North Atlantic, months with many hurricanes were characterized by a well-developed subtropical high-pressure belt, displaced to the north; a deep Icelandic low; a stronger than normal polar vortex with a deep polar trough dipping far southward over the eastern part of the U.S.; a dominant high-pressure ridge over western Canada and the U.S.; and a jet stream displaced northward over these regions. At 200 mb, an anomalous anticyclonic circulation tended to prevail over the subtropical North Atlantic, with stronger than normal upper easterly flow in low latitudes. Positive sea surface temperature anomalies on a seasonal or long-term basis tend to favor the formation of hurricanes.

Dirmeyer, P. A. and K. L. Brubaker (1999). "Contrasting evaporative moisture sources during the drought of 1988 and the flood of 1993." Journal of Geophysical Research, Washington, DC 104(D16): 19383-19397.

Using hourly observed precipitation data, National Centers for Environmental Prediction reanalyses at 6 hourly intervals, and a quasi-isentropic back-trajectory algorithm, we have examined the transport and surface sources of moisture supplying rainfall during the spring and summer over the United States during the drought year of 1988 and the flood year of 1993. These results are compared to calculations using a bulk-transport approach and monthly mean data. We find that about 41% of precipitation over the Mississippi River basin originated as evaporation from the same basin during April-July 1988 and 33% during 1993. During the July peak of the 1993 flood the recycling ratio was considerably lower than in other months, while the source of moisture from the western Gulf of Mexico and Caribbean Sea increased enormously. By contrast, at the June climax of the 1988 drought, the recycling ratio reaches a maximum. We also find a small source region in the eastern subtropical Pacific Ocean during both years, which decreases significantly with the onset of the Mexican monsoon around the beginning of July. The back-trajectory approach represents an improvement over the bulk recycling approach by rejecting the assumption of uniform distributions of rainfall in space and time, instead focusing specifically on the sources and transport of moisture contributing to observed rainfall events.

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

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

Dutta, S. N. and U. S. De (1999). "A diagnostic study of contrasting rainfall epochs over Mumbai." Mausam 50(1): 1-8.

An attempt has made to diagnose the synoptic features and some dynamic and thermodynamic parameters associated with contrasting rainfall situations (on consecutive days) during the monsoon season, over Mumbai. Study has been made for two contrasting monsoon years, viz, 1987 (Bad monsoon year) and 1988 (Good monsoon year). For this study RS data of Mumbai have been used. In many cases heavy rainfall on an isolated day over Mumbai is associated with the following synoptic systems - (a) a trough on sea level chart running along west coast through Maharashtra Coast and (b) a cyclonic circulation (CYCIR) over Gujarat in the lower/middle tropospheric level. At least one of the above two systems ceased to exist on the days of light rainfall. Weighted average value of moist static energy is more on the day of heavy rainfall. In most of the cases convective available potential energy (CAPE) is also more on the day of heavy rainfall. LFC, on most of the cases, is seen to have lowered down on the days of heavy rainfall. Variation in upper air flow pattern and scorer parameter also gave very interesting clues to variation of rainfall on contrasting days.

Elsberry, R. L., L. E. Carr, III, et al. (1998). "Progress toward a generalized description of the environment structure contribution to tropical cyclone track types." Meteorology and Atmospheric Physics, Vienna, Austria 67(1-4): 93-116.

A critical meteorological knowledge base for the application of the Systematic Approach to Tropical Cyclone Track Forecasting of Carr and Elsberry is the environment structure, which is a small set of synoptic patterns and synoptic regions that characterize the tracks. As the original Systematic Approach for the western North Pacific has been applied to the eastern and central North Pacific by Boothe and to the Southern Hemisphere by Bannister et al., the conceptual models of the synoptic patterns have been generalized. Whereas only slight modifications of three of the original four synoptic patterns are required in the two new basin applications, the monsoon gyre pattern of the western North Pacific must be replaced with an upper-low pattern in the eastern and central North Pacific and by a high-amplitude midlatitude trough/ridge in the Southern Hemisphere. An important conclusion is that the environment structure of all tropical cyclones in these three basins could be classified into these small sets. Furthermore, each synoptic pattern/region has a set of characteristic tracks, and a change in environment structure has an associated track change. Comparisons and contrasts of these environmental structures demonstrates that the relative importance of the monsoon trough, subtropical ridge, and midlatitude circulations can account for first-order variations in TC tracks within these three tropical cyclone basins. Summaries of the occurrence of synoptic pattern /region transitions are given for the three basins. Although each TC basin has special characteristics, the general application of the Systematic Approach suggests a unified treatment is possible. Further development along this line is expected to improve the accuracy and consistency of forecasts and warnings.

Evans, J. L. and R. J. Allan (1992). "El Nino/Southern Oscillation modification to the structure of the monsoon and tropical cyclone activity in the Australasian region." International Journal of Climatology, New York, NY 12(6): 611-623.

Streamfunction and velocity potential fields, calculated from monthly averaged station data sets, are composited for ENSO and anti-ENSO extremes in the Australasian region. Four January and four February data sets are used for each of the composites. Gridded sea-surface temperature (SST) and highly reflective cloud (HRC) data are composited in a similar manner. These data are used to investigate the effect of the phase of ENSO on the Australasian summer monsoon and tropical cyclone activity in the region. Changes in the structure of the monsoon are found to be consistent with composited tropical cyclogenesis and cyclone track data. These effects extend to the north and west of Australia, in addition to the signal previously identified in the Queensland region. During ENSO phases, the summer monsoon trough is weak and displaced equatorward, vertical wind shear is reduced and warmer SSTs are found to the north-west of Australia and in the central equatorial Pacific. Tropical cyclone activity is reduced to the north-east of Australia, but increases to the north and north-west of the continent. Owing to the associated changes in the steering flow, coastal crossings are enhanced in Western Australia and the Northern Territory, but suppressed in Queensland. In the anti-ENSO composite, the reverse generally is observed. Features specific to the anti-ENSO are that far fewer storms occur to the north of Australia and storms off the west coast tend to track off-shore, persisting further south. This southward persistence also is evident on the east coast, but here the likelihood of coastal crossing is enhanced compared with the ENSO composite.

Feng, D. and L. Fu (1989). "Main meteorological problems of rice production and protective measures in China." International Journal of Biometeorology, Amsterdam 33(1): 1-6.

China is one of the largest rice producers in the world. Since 1949, the rice production in China has increased considerably. The strong monsoon and continental climate and the varied topography provide suitable conditions for rice growth. However, cold, drought, water logging injury, and other meteorological disasters occur frequently, resulting in unstable yield. This paper briefly introduces natural conditions in China which are favorable for rice production. Attention is focused on the main meteorological disasters and the protective measures adopted in rice production. Some profitable suggestions for China's future rice production are given.

Filippova, M. G. (1997). "On atmospheric moisture balance over East China in the summer monsoon period." Meteorologiya i Gidrologiya [Meteorology and Hydrology.], Moscow, Russia 12: 30-36.

On the basis of summer MONEX (May to August 1979) data, water vapour divergence and moisture budgets are estimated for East China. Water vapour month-averaged integral fluxes interpolated to 2.5 x 2.5 degrees grid points are used to calculate the divergence, D. In May, water vapour sources (positive D regions) are situated to the south of the area under study. For East China, negative D (convergence) and thus water vapour sink is obtained with maximum values (to -140 mm) at the polar front. In June, water vapour convergence increases (to -450 mm) in the subtropical monsoon cell. In July, a convergence zone is found over whole East Asia. A primary maximum (-400 mm at the polar front) moves to north-east with respect to June. A secondary maximum is still located over the South China Sea. In August, the subtropical monsoon reaches midlatitudes of East Asia and, starts weakening by the end of the month, as well as the tropical cyclone does. Over the north China, water vapour convergence zone weakens (to -200 mm). The water vapour budget is estimated for a smaller area (20-40 degrees N, 105-120 degrees E), and it is found to be negative for all the months. This result can reflect generally dry weather in summer of 1979, with relatively weak subtropic monsoon. Mainly, the water vapour is transferred from the area through its east boundary from May to July. Maximum transfer through this boundary occurs in June (-369.9 x 10 super(6) kg/s), which is twice the long-period norm. In August, slightly positive flux through this boundary is obtained.

Gao, S., Y. Zhou, et al. (2002). "Structural features of the Meiyu front system." Acta Meteorologica Sinica [Acta Meteorol. Sinica]. 16(2).

A new subtropical front near the periphery of the West Pacific subtropical anticyclone is found, which is never revealed in previous studies. The coupling of the subtropical front and Meiyu front forms a Meiyu front system (MFS) and is the most direct synoptic system for the Meiyu precipitation along the Mid-lower Reaches of Yangtze River (MRYR) in China. In this paper. The detailed structural features and cloud features of the MFS in 1998 and 1999 are analyzed, which manifests that the MFS is an objective phenomenon over the period of Meiyu along MRYR and the Southwest Japan. Generally, the subtropical front is mainly located between 850 hPa and 500 hPa. The moist southwest monsoon is transported in the passageway between the Meiyu front and the subtropical front. The vertical motion ascends in the passageway and descends on both sides of the MFS, forming the MFS's secondary circulation. A lower TBB band indicated that obvious convective activities are also located in the passageway of MFS. The horizontal wind of MFS is vertically asymmetric.

Gary, W. M. and C.-S. Lee (1984). "Analysis of cross-hemispheric influences on the monsoon trough and tropical cyclone genesis during FGGE and diurnal subsidence differences." National Workshop, 1st, on the Global Weather Experiment: Current Achievements and Future Directions, Woods Hole, MA., July 2: 475-494.

For a number of years, the authors have been studying the cross-equatorial (winter to summer hemisphere) processes that can lead to the day-to-day alterations in the strength of the monsoon trough. These processes are also related to the genesis and intensification of tropical storms. The cross-hemispheric processes that occurred during the FGGE year are currently being studied with the use of the ECMWF analysis. This paper briefly describes how the winter hemisphere can affect 1) low-level cold surge penetration across the Equator following cold front passage, and 2) how upper tropospheric anticyclones of the winter hemisphere can produce an intensification of a tropical cyclone of the opposite hemisphere. This paper also presents ECMWF analysis of the 00Z vs. 12Z diurnal difference in the clear region (10 degrees diameter) subsidence occurring in the subtropical Pacific Ocean during FGGE. These calculations agree with previous rawinsonde composite results and appear to offer further substantiation to the previously hypothesized response process of the troposphere to its large 2-to-1 night vs. daytime differences in net radiation cooling. An attempt is also made to show the general reliability of the FGGE ECMWF analysis with regard to the specification of the large-scale structure of tropical cyclones. The ECMWF wind analyses are generally found to be valid, particularly those large-scale analyses that primarily involve the rotational component of the wind field.

Gatebe, C. K., P. D. Tyson, et al. (1999). "A seasonal air transport climatology for Kenya." Journal of Geophysical Research, Washington, DC 104(D12): 14237-14244.

A climatology of air transport to and from Kenya has been developed using kinematic trajectory modeling. Significant months for trajectory analysis have been determined from a classification of synoptic circulation fields. Five-point back and forward trajectory clusters to and from Kenya reveal that the transport corridors to Kenya are clearly bounded and well defined. Air reaching the country originates mainly from the Saharan region and northwestern Indian Ocean of the Arabian Sea in the Northern Hemisphere and from the Madagascan region of the Indian Ocean in the Southern Hemisphere. Transport from each of these source regions show distinctive annual cycles related to the northeasterly Asian monsoon and the southeasterly trade wind maximum over Kenya in May. The Saharan transport in the lower troposphere is at a maximum when the subtropical high over northern Africa is strongly developed in the boreal winter. Air reaching Kenya between 700 and 500 hPa is mainly from Sahara and northwest Indian Ocean in the months of January and March, which gives way to southwest Indian Ocean flow in May and November. In contrast, air reaching Kenya at 400 hPa is mainly from southwest Indian Ocean in January and March, which is replaced by Saharan transport in May and November. Transport of air from Kenya is invariant, both spatially and temporally, in the tropical easterlies to the Congo Basin and Atlantic Ocean in comparison to the transport to the country. Recirculation of air has also been observed but on a limited and often local scale and not to the extent reported in southern Africa.

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.

Geb, M. and B. Naujokat (1980). "Northern Hemisphere atmospheric conditions in May 1980." Berlin. Freie Univ., Institut fuer Meteorologie, Meteorologische Abhandlungen, Serie B, Grundlagenmaterial 27(5).

In May 1980, high pressure determined the surface and the troposphere over the Arctic and the North Atlantic. Farther south, a belt of intensified cyclonic activity connected so that, within the circumpolar wave patterns (besides the amplified wavenumbers 1 and 4 as a residue of the previous month), wavenumber 2, in particular, was prominent in its climatological position. Geopotential surplus within the entire upper troposphere was dominant in the sub-Tropics and Tropics, a feature that has been observed for 3 yr. According to this fact, the thickness anomaly pattern exhibited large-scale tropospheric temperature surplus over the tropical Pacific and northern Africa. As pointed out in April, at sea level, the positive temperature trend in the Tropics was more marked than before. Conversely, the most intense temperature deficits were registered in Europe. The Arctic showed temperature values below normal on a large scale. The precipitation distribution deficits reflected the splitting of the frontal zones in Europe, Central Asia, and North America caused by a pressure surplus. The onset of the summer monsoon appeared to be enhanced on a large scale only in southeastern Asia. In the stratosphere, the development of the summertime circulation pattern continued: at the 100-mb level, the low centers over northern Asia and Canada/Greenland weakened; at the 50-mb level, an anticyclone developed over the Canadian Arctic, and the low pressure cells shifted toward midlatitudes; at the 30-mb level, the polar high strengthened, and low centers no longer occurred. The temperature distribution, however, showed little change at all three levels; therefore, the deviations from the long-term mean at the 30-mb level show, for the temperature only small, but more negative values, whereas for the height, positive values occurred as well.

Geb, M. and B. Naujokat (1980). "Northern Hemisphere atmospheric conditions in June 1980." Berlin. Freie Univ., Institut fuer Meteorologie, Meteorologische Abhandlungen, Serie B, Grundlagenmaterial 27(6).

June 1980 was characterized generally by an almost complete breakdown of hemispheric waves No. 1 and 4; conversely, the amplified ridges of waves No. 3, 5, and 6 reached their combined position over the northern Atlantic; another superposition of the latter two occurred in the Rocky Mts. Accordingly, three sharpened trough positions were found at the western coast of North America, in Labrador, and in western Europe. At the surface, both the highs over the northestern Pacific and the Azores had strengthened remarkably; together with low pressure over Europe, the weather exhibited monsoonal features within these regions. Because of the dimension of the tropospheric cold pole, the 300-mb-geopotential showed a dipole-shaped vortex with its center in the Siberian sector of the Arctic; the 300-mb-temperature, however, exhibited a warm cell in that region with deviations from the long-year mean of almost +6 degrees . forming a good base for the stratospheric high. Regarding the latitudes 25 degrees N toward the Equator, it was found that the 300-mb-geopotential anomalies had positive values on the complete Northern Hemisphere. The same was valid for the anomalies of tropospheric thickness and temperature. These structures, as usual, were more differentiated at the surface: negative temperature deviations were registered, e.g., in western Africa and southern Asia. On the precipitation map, the quasi-stationary positions of circumpolar troughs and ridges were clearly marked. The rainy season in the Sahel zone, as well as the monsoon in central India, began earlier than in the preceding years. In the stratosphere, the summertime polar anticyclone developed to an intensity distinctly above the long-term mean, in contrast to the previous year. Thus, the positive height deviations persisted which were observed over northern latitudes since March.

Geb, M. and B. Naujokat (1984). "Northern Hemisphere climate report for Feb. 1984." Berlin. Freie Univ., Institut fuer Meteorologie Abhandlungen, Serie B, Grundlagenmaterial 43(2).

In the course of Feb. 1984, the Siberian cold pole in the troposphere regenerated, while its counterpart predominating over Canada and Greenland was spatially confined, appearing partly compensated by positive temperature deviations in the lowest stratosphere (300 hPa). In the midlatitudes, wavenumber 1 dominated, so over the Atlantic and Europe, high pressure prevailed in large areas. Quasi-stationary hemispheric wavenumbers 4-6 were marked similar to 30-50 degrees N. Farther to the north, the Icelandic low, activated by the Greenland cold pole, extended via Jan Mayen and Svalbard as far as the Barents and Kara seas, where the border of pack ice had been driven back toward the northeast during this winter. The generally more detailed pattern of the monthly geopotential anomalies was also reflected by the arrangement of the corresponding thickness and temperature deviations; only the negative anomaly center over West Greenland continued during the three winter months. Compared to the situation of Dec.1983, within the other circumpolar areas, the temperature anomalies were almost arranged inversely. One year after the major El Nino anomaly, the temperature in the 300-hPa center of the 1983 warming appeared remarkably reduced over the tropical Pacific. As usual, the front sides and the axes of the amplified quasi-stationary troughs of the upper airflow were marked by precipitation amounts clearly above normal. Conversely, the upper air confluence over China, showing an extraordinarily strong anomaly of the 300-hPa temperature, slowed down the precipitation production in East Asia. While fringes of the monsoon already reached southern India, the same latitudes of Africa were dominated by dryness. In the stratosphere, at the beginning of the month, a midwinter warming began over eastern Asia and the northern Pacific. Since the middle of the month, it had been developing into a major warming, with a reversal of the wintertime temperture gradient and the breakdown of the westerly wind circulation over northern latitudes until the end of the month. The 30-hPa deviations from the long-term mean show this development with strongly positive anomalies over the Pacific area and strongly negative anomalies over Central Asia and Europe, where the polar vortex was displaced at the first instance.

Godbole, R. V. (1977). "On cumulus-scale transport of horizontal momentum in monsoon depression over India." Pure and Applied Geophysics, Basel 115(5/6): 1373-1381.

A diagnostic method of cumulus parameterization is suggested in which vertical transport of horizontal momentum by cumulus scale is derived by making use of large-scale vorticity as well as divergence budget equations. Data for composite monsoon depression over India available from the earlier studies are used to test the method. As a first approximation, the results are obtained by using only the vorticity budget equation. The results show that in the southwest sector of the monsoon depression, which is characterized by maximum cloudiness and precipitation, there is an excess of cyclonic vorticity in the lower troposphere and anticyclonic vorticity in the upper troposphere associated with the large-scale motion. The distribution of eddy vertical transport of horizontal momentum is such that anticyclonic vorticity is generated in the lower troposphere and cyclonic vorticity, aloft. Cumulus-scale eddies work against the large-scale system and tend to offset the large-scale imbalance in vorticity.

Gongwang, S. (1989). "On the large-scale circulation of the Mei-yu system over East Asia." Acta Meteorologica Sinica, Peking 47(3): 312-323.

The large-scale circulation of the Mei-yu system over East Asia has been reviewed from a dynamical climatological view in this paper. The following arguments have been pointed out: the Mei-yu phenomenon is an occurrence in the transition region between the Indian Summer Monsoon System and the trade wind (or Hadley) system over the tropical North Pacific; the Mei-yu front belongs to a semi-tropical and semi-extratropical weather system; the heavy rain that occurred at the Mei-yu front is caused by the disturbances of subsynoptic systems to the front. The conceptional models for the large-scale circulation and various subsynoptic disturbances of the Mei-yu system have been given.

Gopinathan, C. K. (1984). "India: surface temperature of the equatorial Pacific Ocean and the Indian rainfall." WMO Tropical Meteorology Research Programme.

Results of studies in numerous areas of monsoon study in India are summarized by their investigators. Subjects examined include: surface temperature of the equatorial Pacific Ocean and the Indian rainfall; sea surface temperature variability over the North Indian Ocean, a study of two contrasting monsoon seasons; growth of equatorial waves and the monsoon onset vortex; numerical experiments on rain-producing systems in the tropics; some aspects of the axis of monsoon trough as seen by INSAT imagery; the role of climatic teleconnections in predicting Indian monsoon variability; parametric and power regression models: a new approach to long range forecasting of monsoon rainfall in India; influence of lower stratospheric winds on monsoon rainfall over India; moisture inflow and its contribution to monsoon rainfall over India; mathematical modeling for quantitative precipitation forecasting; and intra-seasonal variation in circulation and rainfall during NE monsoon. Other areas covered are: a mesoscale study of unusually heavy rainfall over south Kerala; some unusually heavy rainfall spells over north India; bay depressions during monsoon 1978; unusual heavy rainfall during January to March 1984 over Peninsular India; some characteristic features of a monsoon depression; unusual rainfall during October, 1974; synoptic study of rainstorms over catchment areas; areas of heavy rainfall using very high resolution satellite imagery; rainfall distribution associated with cyclones; use of satellite data in real time hydrological forecasting; estimation of heavy rainfall using INSAT-1B satellite data; estimation of precipitation and outgoing longwave radiation from INSAT-1B radiance data; large scale precipitation and outgoing longwave radiation from INSAT-1B during the 1986 southwest monsoon season; design storm studies; frequency analysis of short-duration rainfall; quantitative precipitation forecast; study of rainstorms; a statistical forecasting model; monsoon trough; severe local storm; NE coastal hazards due to cyclones; cyclone skew symmetry; influence of solar activity on rainfall over West Bengal; heavy rains in Kerala during SW monsoon in association with tropical storms in South China Sea; interaction of mid-latitude system in the Southern Hemisphere with southwest monsoon; some studies on winter rainfall over Maharashtra, Goa and Gujarat states with special reference to that during 1988 and a correlation between winter and monsoon rainfall over India; synoptic situations associated with spells of strong and weak monsoon over Madhya Maharashtra; evaporative cooling of hail and water droplets below cloud base during the process of down draft from convective clouds, a theoretical approach. Other topics include: periodicities and predictability of summer monsoon rainfall over peninsula; forecasting of hailstorms over India; effects of cross equatorial migration of low pressure vortices on the onset and strengthening of southwest monsoon over India; ITCZ and Indian monsoon rainfall; studies in the upper atmosphere; and disturbances along the Tropical Easterly Jet.

Gordon, A. H. and R. C. Taylor (1975). "Computations of surface layer air parcel trajectories, and weather, in the oceanic Tropics." Honolulu, The University Press of Hawaii 112.

This monograph presents a theoretical investigation of the dynamics of such phenomena as the variations of cloudiness over comparatively short distances observed in India during the summer monsoon, the low level distribution of cloudiness extending over the Tropical Pacific, and the distribution of rainfall over the Gilbert-Ellice and Line Islands. The basis of the approach involves computation of the field of motion in the near surface layer, its divergence from a specified (steady) pressure field, a frictional constraint and, implicitly, a variable Coriolis acceleration. The paths of individual parcels are computed by treating them as steady streamlines under suitable assumptions. Two introductory chapters present an historical survey of the application of mathematical methods and physical concepts to describe the motion of a continuum, in general, and the motion of the atmosphere, in particular; the theoretical mathematics of frictionless flow; and the introduction of friction into flow. A chapter follows describing previous investigations of pressure and wind in low latitudes and five case studies of near-surface trajectories from both the Indian and Pacific oceans. These five examples include some no-drift aircraft flights over the Indian Ocean in June and July 1963, in which an attempt is made to compute a sample steady-state trajectory and to infer some crude aspects of friction; this is followed by three climatological examples--the Marshall Islands, the Indian Ocean, and the Gilbert-Ellice Islands--where some steady state trajectories and the accompanying horizontal divergence are computed. The latter results are compared with available climatological distributions of cloud and rainfall. Also, the following computations of theoretical interest are presented: double near-equatorial troughs symmetrically placed as regards the Equator; a pressure gradient along the Equator; and some computed trajectories in both circular and elliptical isobar systems. An attempt is made to interpret the four climatological cases by means of the divergence equation. The results indicate that the divergence of the pressure gradient force and the Coriolis force is significant in determining the temporal change of the horizontal velocity divergence following the motion. Successful diagnostic results require a knowledge of the pressure field within a few tenths of a millibar over distances of five degrees of latitude.

Grant, K. (1978). "September monsoon depression at Masirah, Oman." Meteorological Magazine, Bracknell, Eng 107(1272): 218-222.

Details are given of the later stages of an Indian monsoon depression that travelled unusually far westward into Arabia in Sept. 1976.

Gregory, S. (1989). "Changing frequency of drought in India, 1871-1985." Geographical Journal, London 155(3): 322-334.

The impact of drought on society and economy in India is intensified if there is an unusually high frequency of such conditions within a relatively limited time scale. For 115 yr (1871-1985), all 86 successive 30-yr periods and all 106 successive 10-yr periods have been analyzed from data for summer, i.e., June-Sept., monsoon rainfall for ten macroregions in nonmountainous India. Drought has been defined simply as unusually low monsoon rainfall, in terms of the driest 10% of years; deficits, below the average of >20%; and larger deficits in some regions. Temporal changes in the frequency of these conditions across all 30- and 10-yr periods are graphed and discussed for each region, and for all-India; and those periods with frequencies greater than might be expected at random are distinguished. Major contrasts in timing are demonstrated between the northeast and most of the rest of the country, with the far southwest not fitting into either category. The spatial pattern of temporal concentrations of drought occurrences are mapped, and the need is stressed to consider potential socioeconomic problems in India, if drought frequencies from the early part of this century were to return.

Gu, R.-y., X.-d. Liu, et al. (1992). "The previous stratosphere characteristics of El Nino." Chinese Science Bulletin, Rego Park, NY 37(10): 842-846.

El Nino usually happens with the anomaly of general circulation of the atmosphere and climate in the world. El Nino has close statistical relationships with the rainfall decrease in Africa, the monsoon weakening in India, and the Australian aridity. In recent years, it has been pointed out that there is a certain correlation between El Nino and Chinese climate and weather. In an El Nino year, the summer temperature is lower than normal in northeast China. The development and occurrence of El Nino can also cause the anomalies of rainfall in the Changjiang River valley and typhoons in China. Therefore, the forecasting of El Nino events has become a very important subject studied by meteorologists and oceanologists in recent years. Many scholars pointed out that the occurrence of El Nino has a relationship with the anomaly of air circulation and climate of troposphere in winter in middle latitudes and some researchers think that El Nino happens because of warmer water gathering in the west Pacific and Kelvin waves caused by the collapse of the trade winds, or because of the subsiding of trade winds caused by the weakening of high pressure in the southeast Pacific. But all these works are limited in troposphere and are not enough to be used to forecast El Nino. As an important part of the whole general circulation of atmosphere, stratosphere has a close relationship with troposphere. Pointed out recently is that the seasonal and annual variations of circulation in stratosphere appear earlier and stronger than those in troposphere. Now that there exist correlations between El Nino and the troposphere, then what is the expression of El Nino stratosphere? And is there further information in stratosphere than in troposphere before El Nino? In this paper, all these questions are discussed.

Gupta, A. and A. Muthuchami (1991). "El-Nino and tropical storm tracks over Bay of Bengal during post monsoon season." Mausam, New Delhi, India 42(3): 257-260.

The role of El-Nino in modulating tropical cyclone motion over Bay of Bengal during post monsoon season has been examined. Storms which formed during the years 1901-1987 have been classified into recurving or those of which crossing north of 17 degrees N and non-recurving or those of which crossing south of 17 degrees N on the east coast of India. It has been found that in most of the cases (87%) during El-Nino years, the tropical cyclones which formed over Bay of Bengal crossed south of 17 degrees N, i.e., south Andhra Pradesh-Tamil Nadu coast, whereas tropical cyclones formed during the year prior to the El-Nino years [El-Nino (-1) year] are seen crossing mostly (in 79% of cases) either north of 17 degrees N or recurving in northeastward direction. In other years this kind of behavior is not generally observed. The correlation between southern oscillation indices and the fractional values of storms crossing south of 17 degrees N for the period 1901-1987 (n=87) is found to be -0.63 which is significant at 1 per cent level.

Gupta, H. N. and O. P. Jindal (1987). "Unprecedented heavy rainfall in Jaipur (Rajasthan) during 18-20 July 1981." Mausam, New Delhi 38(3): 362-364.

The synoptic situation leading to an unprecedented and all-time record heavy rain, which occurred in Jaipur during the period July 18-20, 1981, has been studied. The heavy rains occurred during a monsoon low, which formed over northwestern India within the monsoon trough--an uncommon synoptic situation. The low moved slowly in a southeasterly direction until July 20 and merged with the monsoon trough over northwest Madhya Pradesh. Jaipur city recorded 82 cm of rain and Jaipur Airport 62 cm during the 3-day period. The heaviest 24-hr rainfall amounts of 35 and 33 cm were recorded on July 19, 1981, at Jaipur city. The circulations, the embedded vortices and tracks of the pressure system, and the winds are described by using 500- and 850-mb sea level charts. From the study, it is concluded that monsoon lows may develop as far inland as Rajasthan within the monsoon trough system when it shifts north. These systems manifest characteristics of a well-developed intense monsoon depression. The low-pressure areas originating in the high latitudes may show an easterly movement, giving the impression of being western disturbances.

Hamilton, M. G. (1977). "Some aspects of break and active monsoon over southern Asia during summer." Tellus, Stockholm 29(4): 335-344.

At least three synoptic phases of the summer monsoon can be identified north of 10 degrees N. Two of these phases--the break and active monsoon--are extremes. Patterns of cloudiness and rainfall for these two phases differ substantially. These indicate differences in the geographic location and intensity of tropospheric energy sources. Tropospheric circulations over the equatorial Indian Ocean during break and active monsoon also differ. A break is often accompanied by the development of a trough in the lower troposphere northeast of Gan; this appears to enhance rainfall over southeast India. Although cause and effect are difficult to separate with scanty aerological data, synoptic variation over the equatorial Indian Ocean east of 60 degrees -65 degrees E may influence rainfall over western and southern India.

Handler, P. and B. O'Neill (1987). "Simultaneity of response of Atlantic Ocean tropical cyclones and Indian monsoons." Journal of Geophysical Research, Wash., D.C 92(C13): 14621-14630.

To demonstrate global simultaneity in climatic response to volcanic aerosols, climate events were selected from two regions separated by similar to 180 degrees long. These events are the Indian monsoon and the frequency of tropical cyclones in the North Atlantic, both of which occur during the summer season in the Northern Hemisphere. The simultaneity of these two regions is shown through several different methods. As a first step, a strong linear correlation is shown between the deviations from the local averages of these two widely separated climate events. From 1900 to 1986, the correlation is above the 99.75% significance level. In the case of the Indian monsoon, a decrease in solar radiation results in a nonlinear decrease in precipitation. In the case of North Atlantic tropical cyclones, decreased radiation results in decreased occurrence. The Indian monsoon and tropical cyclone seasons are divided, each, into two classes, above or below the local average. The association of this seasonal classification is examined in a chi super(2) analysis by using a 2 x 2 contingency table, where chi super(2) = 13.74 for the period 1900-1986. The probability of achieving this degree of association by chance is less than two parts in 10,000. The causal element of the observed simultaneity is hypothesized to be the presence of low-latitude volcanic aerosols. Over the period 1900-1986, there are 19 seasons in which a known, reported low-latitude aerosol could have affected the climate anomalies without interference from preexisting, or concurrent, high-latitude aerosols. Of the 19 seasons, 94% had below-normal frequency of tropical cyclones, and in 73% of the seasons, the precipitation of the Indian monsoon was below normal. A similar analysis is performed for high-latitude aerosols ( greater than or equal to 30 degrees lat.), where opposite results are expected. In this case, there are 13 seasons, 46% with above-normal frequency of tropical cyclones and 77% with above-normal Indian monsoons. The Indian monsoon shows a significant response to high-latitude aerosols, whereas the tropical cyclone frequency does not. Data prior to 1900 (1871-1899) are shown for completeness. It is concluded that there is a significant correlation between the frequency of tropical cyclones in the North Atlantic and the Indian monsoon, and there is little chance that this correlation is due to random events. From the Atlantic to the Indian subcontinent, there are simultaneous climatic anomalies in conjunction with the presence of low-latitude aerosols. While it is possible to conceive of a complex set of internal teleconnections to bring about this climate pattern, the simplest and most economical hypothesis is to assume that global forcing through the reduction of solar radiation resulting from the presence of stratospheric volcanic aerosols may play a major role in producing the observed climate anomalies.

Hanstrum, B. N., G. Reader, et al. (1999). "The South Pacific and southeast Indian Ocean tropical cyclone season 1996-97." Australian Meteorological Magazine, Canberra, Australia 48(3): 197-210.

Tropical cyclone occurrences were above the long-term averages during the 1996-97 season. The weak La Nina phase which characterised 1996 declined and some early El Nino indicators emerged by the end of the season. These included the appearance of strong westerly equatorial wind anomalies near the date-line, increasing sea-surface temperature in the near-equatorial central and eastern Pacific, a fall of the Southern Oscillation Index to negative values and increased convective activity in the South Pacific convergence zone. The monsoon in the summer hemisphere was of average development or better, with strongest anomalies in the southwest Pacific. Three major cycles of the 30 to 60-day intraseasonal oscillation were diagnosed. The 26 cyclones that formed spanned every month (July 96-June 97) except August and September.

Harihara Ayyar, P. S., S. D. S. Abbi, et al. (1975). "Assessment of water potential contributed by tropical storms of Bay of Bengal during post monsoon period." Indian Journal of Meteorology, Hydrology, & Geophysics, Delhi 26(2): 227-231.

A few typical cases of tropical storms that originated in the Bay of Bengal during the postmonsoon months (Oct.-Dec.) were studied with respect to their water potential. Isohyetal analysis was made of the rainstorms associated with these disturbances in the course of their movement. The total volume of water contributed over land south of 16 degrees N lat. by each of these cyclonic disturbances has been computed and is presented.

Harr, P. A. and R. L. Elsberry (1991). "Tropical cyclone track characteristics as a function of large-scale circulation anomalies." Monthly Weather Review, Boston, MA 119(6): 1448-1468.

Factors that contribute to intraseasonal variability in western North Pacific tropical cyclone track types are investigated. It is hypothesized that the 700-mb large-scale circulation can affect tropical cyclone track characteristics by enhancing or excluding genesis in certain regions, and concurrently prohibiting or favoring recurving versus straight tracks. A track-type climatology indicates that genesis location alone may explain some of the variability in track type. Although some genesis regions have no preference for straight-moving or recurving tracks, a formation north of 20 degrees N or east of 150 degrees E and north of 10 degrees N favors a recurvature track. These recurving storms are classified as recurving-north, and recurving storms that form in regions with nearly equal probability of straight or recurving tracks are classified as recurving-south. A compositing technique is used to define anomalous 700-mb large-scale circulations that exist during the formation of tropical cyclones that subsequently follow either a straight track or one of the two types of recurving tracks. Anomalous circulations associated with extended periods that do not contain any tropical cyclones are also identified. Physically and statistically different anomalous large-scale circulation patterns exist at the time of genesis for storms following each track type and for inactive periods. The large-scale anomalies describe variations in the positions and intensities of the monsoon trough and subtropical ridge. During genesis of straight-moving and recurving-south storms, anomalous large-scale horizontal cyclonic shear exists throughout the South China Sea and Philippine Sea. During straight-moving storms, cyclonic shear increases because of anomalous easterlies along the southern boundary of an enhanced subtropical ridge. During recurving-south storms, anomalous equatorial westerlies and cross-equatorial flow from the Southern Hemisphere act to increase the cyclonic shear. The track-type climatology is used to predict the subsequent track type based only on genesis location. In a second scheme, the distributions of anomalous 700-mb zonal wind components in 5 degrees latitude bands averaged between 100 degrees and 140 degrees E are used to predict the most likely track type. The large-scale 700-mb anomalies at genesis time determine the subsequent track type in a majority of cases. The skill of this simple scheme exceeds that from the climatological probability of track type.

Harr, P. A. and R. L. Elsberry (1995). "Large-scale circulation variability over the tropical western North Pacific. Part I: Spatial patterns and tropical cyclone characteristics." Monthly Weather Review, Boston, MA 123(5): 1225-1246.

The basic structure of the variability of the large-scale circulations over the tropical western Pacific is investigated with respect to its influence on tropical cyclone characteristics. A vector empirical orthogonal function analysis and fuzzy cluster algorithm are applied to a 9-yr dataset to define six recurrent 700-mb circulation patterns that represent large-scale variabilities associated with the monsoon trough and subtropical ridge. Five of the cluster patterns, which contain 48% of the sample, define combinations of active (inactive) monsoon trough and strong (weak) subtropical ridge circulations. The sixth cluster, which contains 26% of the data sample, depicts small deviations from the long-term climatology. After the cluster centers are defined, the fuzzy cluster coefficients are used to identify a seventh cluster, which contains the remaining 26% of the circulation patterns that could not be classified within any of the original six clusters. The 700-mb circulation patterns are physically consistent with outgoing longwave radiation anomalies and the 200-mb streamfunction and velocity potential anomalies. Active and inactive monsoon trough patterns are related to large-scale velocity potential anomalies over the tropical western Pacific and Indian Ocean basins. Anomalous cyclonic circulations are found to be regions of anomalous convergence at 700 mb, divergence at 200 mb, and enhanced large-scale convection. Anticyclonic anomalies are regions of anomalous 700-mb divergence, 200-mb convergence, and reduced large-scale convection. Variability of the subtropical ridge is associated with large-scale, 200-mb streamfunction anomalies that are related to variations in the midlatitude longwave pattern. Tropical cyclone activity is found to be related significantly to the variability of the monsoon trough described within the cluster framework. Active (inactive) periods are found to occur when the large-scale circulation anomalies are contained within clusters that represent an active (inactive) monsoon trough. However, grouping of clusters based exclusively on the variability of the monsoon trough does not adequately account for the variability in tropical cyclone track types. Comparisons between observed tropical cyclone track characteristics and the cluster definition at the time the tropical cyclone reaches tropical storm strength identify a statistically significant relationship between track type (straight-moving versus recurving) and the individual five cluster patterns that describe the variability of the monsoon trough and subtropical ridge. No relationships are found between tropical cyclone characteristics and the cluster that represents small deviations from the climatological mean or the cluster that is defined to contain circulation patterns not classified in any of the original six clusters. It is concluded that the cluster patterns define the basic structure of large-scale circulation variability over the tropical western Pacific and that these structures are related to tropical cyclone characteristics.

Harr, P. A., R. L. Elsberry, et al. (1996). "Transformation of a large monsoon depression to a tropical storm during TCM-93." Monthly Weather Review, Boston, MA 124(12): 2625-2643.

Data obtained during two aircraft observing periods (AOP) from the TCM-93 mini field experiment are used to describe the transformation between 5 degrees and 10 degrees N of a large depression in the western North Pacific monsoon trough into a tropical cyclone over a 36-h period. The transformation is defined to occur in three stages. Although a large mesoscale convective system (MCS) was present along the eastern periphery of the monsoon depression during the preorganization stage characterized by observations from the first AOP, the overall convective organization of the broad circulation is weak. The structure of the MCS provided a midlevel subsynoptic contribution to the vorticity of the monsoon depression and contributed to a shift in the center of the monsoon depression circulation between 800 and 600 mb toward the MCS location. However, the presence of unsaturated downdrafts associated with the MCS perturbed the low-level thermodynamic conditions and contributed to the rapid decay of the MCS. Slow intensification of the monsoon depression circulation during the preorganization stage is primarily due to favorable interactions with large-scale mean and eddy circulations at both upper and lower levels. The overall convective signature was observed in hourly satellite imagery to become more organized during a 24-h period between the two AOPs. This organization stage was characterized by the formation of a new MCS near the midlevel circulation of the decaying MCS from the preorganization stage. Satellite imagery indicates that the broad monsoon depression began to organize around the new MCS and the outer convection started to be oriented in large principle bands. During the transformation to a tropical storm during the second AOP, the outer principal bands appear to separate the inner circulation of the monsoon depression from the large-scale monsoon trough environment. Convection rapidly develops along the periphery of the inner circulation that now contains a vigorous central updraft and high values of equivalent potential temperature that extend to the middle troposphere. Although several episodes of MCS generation and decay occurred throughout the development of the monsoon depression, it is hypothesized that the subsynoptic processes in the MCS during the first AOP and the MCSs that formed immediately following the second AOP contributed to the concentration of the monsoon depression center and transformation to a tropical cyclone.

Harr, P. A., M. S. Kalafsky, et al. (1996). "Environmental conditions prior to formation of a midget tropical cyclone during TCM-93." Monthly Weather Review, Boston, MA 124(8): 1693-1710.

During a 10-day period in the Tropical Cyclone Motion (TCM-93) field experiment over the tropical western North Pacific, tropical cyclone formation occurred in association with persistent deep convection that was observed over low-level, north-oriented confluent flow between a large monsoon gyre to the west of a strong subtropical ridge. The convection was also modulated by a strong diurnal cycle with a convective maximum just before dawn and a convective minimum during the late afternoon. Observations from two aircraft observing periods (AOPs) during two consecutive daytime periods identified three distinct mesoscale convective vortices (MCVs) in the persistent deep convection. During the initial AOP (AOP-1A), a well-defined mesoscale circulation at 500 mb was located directly above the strong low-level, south-southwesterly confluent flow. However, reduction in convection and associated midlevel forcing during the convective minimum period contributed to the decay of the MCV before it could penetrate downward through the strong low-level flow to tap ocean surface energy sources. During the second AOP (AOP-1B), which was approximately 24 h after AOP-1A, two MCVs were identified by aircraft observations. A northern MCV, which dissipated shortly after the AOP, had a structure similar to the observed MCV in AOP-1A and was also located directly above the strong low-level north-oriented flow. A second midtropospheric MCV over the southern portion of the aircraft operating area extended down to 850 mb and was located in the cyclonic shear of the low-level flow. Although convection over the large area was decreasing during the diurnal minimum, several convective cells formed and grew in association with local low-level confluence between the low-level MCV circulation and the large-scale flow. In contrast to AOP-1A, this convection persisted and acquired a rotation as part of a northward-moving circulation that can be traced to a small low-level mesoscale circulation in satellite visible imagery approximately 10 h after the AOP as the same circulation observed over the southern region of AOP-1B. Satellite visible imagery documents the explosive convective development associated with the low-level circulation that led to the formation of Tropical Storm Ofelia. It is concluded that the southern MCV in AOP-1B was able to persist because of its extension to low levels, which was linked to its location on the cyclonic shear side of the strong low-level flow.

Hastenrath, S., A. Nicklis, et al. (1993). "Atmospheric-hydrospheric mechanisms of climate anomalies in the western equatorial Indian Ocean." Journal of Geophysical Research, Washington, DC 98(C11): 20219-20235.

Atmosphere-ocean mechanisms of rainfall anomalies at the coast of eastern Africa are studied using long-term ship observations in the Indian Ocean, surface current measurements, subsurface casts, upper air analyses by the European Centre for Medium Range Weather Forecasts, rain gauge series in eastern Africa and India, and an index of the Southern Oscillation (SO), the high-SO phase being defined by anomalously high/low pressure at Tahiti/Darwin. The causalties of precipitation anomalies at the coast of eastern Africa differ for the two rainy seasons centered on April-May and October-November, and only the latter is strongly related to the SO. In the high-SO phase, April-May pressure is low over the entire Indian Ocean domain, whereas in October-November, pressure is high in the west and low in the east. Concomitantly, surface waters are anomalously cold in the west, and strong westerlies sweep the equatorial zone of the Indian Ocean. Eastern African rainfall anomalies are related to the SO through a combination of cooperative mechanisms that function most effectively in the boreal autumn rainy season of eastern Africa. (1) Equatorial westerly winds are conducive to lower tropospheric divergence over equatorial East Africa, and in the high-SO phase these are accelerated, especially in October-November, owing to the anomalous eastward pressure gradient. (2) The equatorial westerly winds drive the eastward equatorial jet in the upper hydrosphere, which entails cold-water upwelling in the western extremity of the basin where sea surface temperature further hydrostatically affects the zonal pressure gradient and thus feeds back into the equatorial westerly winds. (3) In addition, cold-water anomalies in the western Indian Ocean, most pronounced in October-November during the high-SO phase, also suppress convection. (4) In the high-SO phase, the Indian summer monsoon tends to be strong, leaving behind an anomalously cold western Indian Ocean, which in turn feeds into mechanisms 1 to 3. The eastward equatorial jet thus has a role to play in feedback mechanisms contributing to the anomalies of the boreal autumn rains at the coast of eastern Africa.

Hautbois, M. (1976). "Drought of Nov. and Dec. 1974 in Moroni (Great Comore)." Revue de Geographie Alpine, Grenoble 64(2): 271-280.

The Great Comore is a tropical island in the Indian Ocean. In the rainy season, it often remains dry. This island has a maritime tropical climate with two seasons and goes through a pseudo monsoon that may occur later because of intense activity of the Southern Hemisphere. Inroads of polar air masses regenerate the anticyclones and prevent the formation of the south African's hibernal depression. So, the ITCZ remains at 10 degrees S lat., and the dry season (or the intermediate season) subsists over the Comoro Islands. The recent volcanic structure of the Great Comore increases dryness: because of the lack of springs, water infiltrates immediately.

He, J., X. Zhou, et al. (1995). "Numerical study of Ural blocking high's effect upon Asian summer monsoon circulation and East China flood and drought." Advances in Atmospheric Sciences, Beijing, China 12(3): 361-370.

In terms of Kuo-Qian p-sigma incorporated coordinate five-level primitive equation spheric band (70 degrees N-30 degrees S) model with the Ural high's effect introduced into it as initial and boundary conditions, study is made of the high's influence on Asian summer monsoon circulation and dryness/wetness of eastern China based on case contrast and control experiments. Results show that as an excitation source, the blocking high produces a SE-NW stationary wavetrain with its upper-air anticyclonic divergent circulation (just over a lower-level trough zone) precisely over the middle to lower reaches of the Changjiang River, enhancing East Asian westerly jet, a situation that contributes to perturbation growth, causing an additional secondary meridional circulation at the jet entrance, which intensifies the updraft in the monsoon area. As such, the high's presence and its excited steady wavetrain represent the large-scale key factors and acting mechanisms for the rainstorm over the Changjiang-Huaihe River catchment in the eastern part of the land.

Hell, R. M. and R. K. Smith (1998). "A monsoon depression over northwestern Australia. Part I: Case study." Australian Meteorological Magazine, Canberra, Australia 47(1): 21-40.

A diagnostic study of a monsoon depression that developed over northwestern Australia in February 1994 is presented. The analyses are based on gridded data from the Australian Bureau of Meteorology's Tropical Analysis System. After remaining quasi-stationary for several days after its formation in the monsoon trough, the depression drifted slowly southwestwards along the coast of Western Australia and eventually weakened. The evolution is exemplified by time-height cross-sections of various kinematic quantities as well as the apparent sources of heat, moisture and potential vorticity. A prominent feature of these diagnostic fields is the impact of convective and diabatic processes on the development. The structure of the depression was very similar to the few monsoon depressions that have been documented over the Indian subcontinent. The formation of the depression coincided with the passage of an upper-level mid-latitude trough and a low-level anti-cyclone to the south, but the extent to which the genesis was influenced by these disturbances is unclear.

Hendon, H. H., N. E. Davidson, et al. (1989). "Australian summer monsoon onset during AMEX 1987." Monthly Weather Review, Boston 117(2): 370-390.

The onset of the Australian summer monsoon during 1986-1987 is examined by using gridded tropospheric winds and surface pressure data from the Australian Bureau of Meteorology Tropical Region Analyses. Dramatic and sudden circulation changes on the synoptic and larger scale are known to occur at onset of the monsoon. The enhanced observing network during AMEX-1987 afforded an excellent opportunity to study these changes as the onset occurred during the experiment. During Nov. 1986 through early Jan. 1987, anomalous convection and low-level westerly winds persisted in the central equatorial Pacific, associated with an El Nino-Southern Oscillation event. This anomalous convection forced a large-scale sinking, dry southeasterly flow over the Australian Tropics, inhibiting the onset of the monsoon. In early Jan., the anomalous ENSO convection in the central Pacific diminished rapidly, apparently due to the passage of the downward branch of a 40-50-day oscillation event. Thus, the attendant dry sinking motion over the Australian Tropics diminished, and monsoon onset subsequently occurred in the second week of Jan. Onset in the Australian region appears to have been triggered by the arrival of a westward moving equatorial wave disturbance. This synoptic-scale disturbance appears to have originated in the ENSO westerlies in the central Pacific just before their temporary demise in early Jan. It propagated at least 5000 km across the Pacific into the Australian region. Synoptic-scale low-level moist northerlies resulting from the wave drastically increased the low-level humidity, while the wave's convergence appears to have initiated organized convection over the Australian region. Subsequently, in a matter of one to two days, monsoon convection and low-level westerlies developed over a longitudinal span of similar to 40 degrees . The synoptic-scale wave disturbances also appear to be associated with formation of tropical cyclones in the region soon after onset. The subsequent expansion of the monsoon westerlies after onset results from a combination of an amplification of the synoptic-scale wave disturbance in the Doppler-shifted group velocity direction (eastward) and by the passage of a 40-50-day oscillation event. From a thermodynamic viewpoint, substantial but unrealizable conditional instability existed over the Australian Tropics prior to the monsoon onset. Because of the lack of low-level saturation (from the dry sinking circulation produced by the ENSO anomaly), substantial lifting was required to achieve buoyancy prior to onset. The onset process appears to be one in which initial development of convection induced by synoptic convergence and moisture advection cools and further moistens the lower troposphere, and thereby reduces the degree of lifting required to achieve buoyancy. Onset occurs as a dramatic blowup of convection over a large longitudinal span ( similar to 40 degrees ) when the lifting required for buoyancy achieves a minimum, but prior to the loss of deep conditional instability from the vertical transport of heat and moisture by the monsoon convection.

Hingane, L. S. (1993). "Some analogous synoptic features associated with the ozone minima over the northwest Pacific and southeast Asia." Meteorological Magazine, London, England 122(1448): 70-74.

Global minima in total ozone occur over the northwest Pacific during the active winter monsoon period and over southeast Asia during the active summer monsoon period. The Earth's highest tropopause level appears during the occurrence of ozone minimum over these regions. Further, the Earth's coldest monthly mean temperature at around the 100 hPa level during the corresponding months of ozone minimum is also seen there. The data for outgoing long-wave radiation for the Earth show minimum values over the northwest Pacific during January and over southeast Asia during July indicating deep convection over these areas. The monthly mean of rainfall takes the highest global value during this period. An interpretation is offered that the thickness of the ozone-rich layer in the lower stratosphere is reduced by the overshooting of tropospheric ozone-poor air by intense convective activities.

Hirasawa, N. and T. Yasunari (1990). "Variation in the atmospheric circulation over Asia and the western Pacific associated with the 40-day oscillation of the Indian summer monsoon." Journal of the Meteorological Society of Japan, Tokyo, Japan 68(2): 129-143.

Through use of the outgoing longwave radiation (OLR) and 700 mb height fields for 1979, an investigation was conducted of the variation of the atmospheric circulation over Asia and the western Pacific associated with the 30-60 day variation of the Indian summer monsoon. Results of the analysis of the OLR indicate that convection over the northwestern Pacific along 15 degrees N is active slightly before the active phase of the Indian monsoon over central India, while there is a decrease in convective activity prior to the break phase. This active convection (between 140 degrees E and 150 degrees E) propagates southward with a period of 40 days from 15 degrees N to the equatorial zone. The cloudiness to the north of the Tibetan Plateau (around 55 degrees N, 75 degrees E) and over the subtropical high region (southeast of Japan) reaches a minimum slightly before the active phase of the Indian monsoon. Conversely, cloudiness reaches a maximum prior to the break phase of the Indian monsoon. From the results of the analysis of the 700 mb geopotential heights, it was found that to the north of the Tibetan Plateau the maximum cloudiness corresponds to the stagnation of the trough while the minimum cloudiness is associated with the development of the ridge. The position of the subtropical high shifts northward (along 25-30 degrees N) slightly before the active phase of the Indian monsoon and shifts southward (along 10-20 degrees N) slightly prior to the break phase. The phase of the 30-60 day variation to the north of the Tibetan Plateau precedes that of the subtropical high region. These results suggest a close association among the 30-60 day variation of the Indian monsoon, the convection over the western Pacific, the westerly-wave movements over the Asian continent and the subtropical high in the western Pacific. These large scale interactions affect the weather regime around Japan during the Baiu season. The meridional position of the Baiu front (east of 130 degrees E) around Japan shifts from 40 degrees N, when the subtropical high shifts northward, to 30 degrees N when the subtropical high shifts southward. This is due to the variation of the meridional position of the subtropical high, which is associated with the 40 day variation of the monsoon. The meridional position of the Mei-yu front (west of 130 degrees E), in contrast, does not exhibit a cyclical variation.

Holland, G. (1979). "Observations of a vortex embedded in a monsoonal flow." Australian Meteorological Magazine, Canberra 26(1): 19-24.

In a data-sparse area such as the Australian region, analysts are often required to interpret instantaneous views of vortexes, such as given on a satellite mosaic or radar photograph, in terms of the prevailing flow patterns, without the aid of any synoptic observations in the immediate vicinity. It is not always appreciated, however, that the circulation, as viewed on a satellite mosaic or radar photograph, is in a frame of reference to the circulation. For a large, slowly moving vortex, this will cause negligible differences, but for a small, rapidly moving vortex, literal interpretation of the circulation without an explanation of vortex movement may result in large errors. It is the purpose of this paper to describe an example of a small, rapidly moving vortex that was noted during the preparation of tropical cyclone case histories for the 1975-1976 season in northern Australia. On March 14, 1976, a weak tropical depression formed to the southwest of the Indonesian island of Sumba and moved eastward under the influence of a prevailing westerly monsoon. The depression deepened into tropical cyclone ``Linda'' for a brief period on the 16th, but rapidly decayed as it was absorbed into the circulation around an intense monsoonal low over northern Australia. The track and estimated central pressures are shown. The decayed remains of ``Linda'' were observed on Darwin radar during March 17, as a well-defined, although ragged, vortex; however, synoptic observations in the near vicinity admit no such circulation, but merely a short-wave perturbation on the prevailing westerly flow with a strong cyclonic shear. This is illustrated in figures that show the prevailing synoptic situation at the surface, a time cross section of upper winds and surface observations at Darwin, and a composite of radar echo velocities (derived from movement of major echoes over the period 0430-0500 hr GMT) and synoptic observations around the disturbance. The radar echo velocities may be interpreted as representative of the low-level circulation (Watanabe 1963). A detailed analysis is not appropriate because of the varying observations presented; however, it is obvious that the differences are caused by the motion of the vortex relative to the Earth ( similar to 12 m/sec). In a frame of reference attached to the moving system, it is seen as a closed circulation with a substantial amount of its vorticity contained in the trajectory curvature, whereas in a frame of reference on the Earth, it appears as a small perturbation with nearly all its vorticity contained in the shear of the horizontal wind.

Holland, G. J. (1986). "BMRC Australian Monsoon Experiment: AMEX." American Meteorological Society, Boston, Bulletin 67(12): 1466-1472.

The BMRC Australian Monsoon Experiment is part of a concerted tropical research program aimed at improving the understanding of the physics and dynamics of tropical weather systems. It is based upon the collection of high-density tropical upper air soundings and radar data during two observational phases in Oct. 1986 and Jan.-Feb. 1987. The objectives, background, and rationale for this program are described together with an overview of the design and timetable of the observing component.

Hoskins, B. J. (1991). "Towards a PV- Theta view of the general circulation." Tellus Series A-B, Stockholm, Sweden 43A-B(4): 27-35.

In recent years, there has been a resurgence of interest in using isentropic coordinates and Rossby-Ertel potential vorticity (PV) for diagnosing the behaviour of middle latitude synoptic systems. Such a PV- theta analysis may also prove important in providing insight into the global circulation of the atmosphere. Apart from the isentropic diagnostic of D. Johnson and collaborators, some quasi-geostrophic studies and recent studies of stratospheric behaviour, there has been little work in this area and our present understanding is very limited. The object of the present paper is to stimulate such studies by presenting some initial results from continuing research. A three-fold division of the atmosphere is discussed. The ``Overworld'' is the region encompassed by isentropic surfaces that are everywhere above the tropopause. In the ``Middleworld'', the region with isentropes crossing the tropopause but not striking the Earth's surface, the isentropic zonal and time mean of PV exhibits interesting regions of enhanced and diminished gradients. The isentropic transient eddy advection of PV exhibits a dipolar distribution about the tropopause, suggestive of PV mixing. The marked PV signature of the Asian summer monsoon on one particular Middleworld isentrope is shown and the mean isentropic advection of PV shows interesting features. For the ``Underworld'', in which isentropic surfaces intercept the surface of the Earth, a PV- theta analysis yields a novel constraint linking low-level drag and diabatic heating. This constraint links ``westerlies'' and ``cooling'', and ``easterlies'' and ``heating'' in some average sense. The result is discussed in terms of the Southern Hemisphere strong surface westerlies and the circulation associated with the Asian summer and winter monsoons.

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

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

Huang, J., Q. Zhu, et al. (1997). "The characters of low-frequency circulation around the globe and its relationship with the flood/drought in the Changjiang River Valley." Journal of Tropical Meteorology, Guangzhou, China 13(2): 146-157.

In this paper, a concret analysis was made on the characters of the low frequency wind and velocity potential fields around the time of Meiyu. It is found that remarkable distinct circulation patterns in the low-frequency wind fields around the globe not only exist in the drought (1981, 1985, 1988) and flood (1980, 1983) years, but also exist in the stages of the drought (or flood) years when precipitation is increasing or decreasing. Concentrating on the years of 1980 and 1988, we find that it is caused by the wave in the low frequency velocity potential fields which connect the precipitation in the Changjiang River valley with the low frequency wind fields around the globe. In the year of 1980, precipitation responds quite well to the northward propagation of LFO in the East Asia monsoon region and the vortex train propagating eastward in the high latitudes of Southern Hemisphere. In the year of 1988, variation of precipitation was closely related with the movement of the low-frequency vortex which originates from the small low-frequency vortex in the east of the tropical Pacific. It is thought that heat/cold source pattern and Walker circulation can be the mechanism which affects the precipitation, while the mechanism in 1988 remains to be discussed.

Inamdar, S. R. and S. V. Singh (1993). "Relationship between circulation and rainfall over India during the southwest monsoon season. Part II: 700 hPa contour height field and some synoptic indices." Theoretical and Applied Climatology, Vienna, Austria 48(1): 1-14.

Concurrent and lag relationships of 700 hPa contour heights over the Indian region and some large scale synoptic indices with rainfall distribution over various parts of India have been studied on a 1-day to 7-day basis by using 10 years (1966-1975) of data. Important dynamic influences causing rainfall over various parts of the country have been identified by the preparation of concurrent and lag-correlation charts. Multiple regression equations have also been developed for prediction of daily, 3-day and 5-day rainfall by using the synoptic indices. Positive skills with higher values over central India and the west coast have been obtained.

Iwasaki, T. and H. Kitagawa (1998). "A possible link of aerosol and cloud radiations to Asian summer monsoon and its implication in long-range numerical weather prediction." Journal of the Meteorological Society of Japan, Tokyo, Japan 76(6): 965-982.

The influence of aerosol and cloud radiations upon the Asian summer monsoon was studied by using the global numerical weather prediction (NWP) model at the Japan Meteorological Agency (JMA). We parameterize both the direct and indirect effects of aerosols on radiative processes. In addition, criteria of cloud diagnosis are modified to enhance the cloud cover over the land in contrast to that over the ocean, considering that clouds form more easily over the land due to surface inhomogeneity and stay longer in the atmosphere due to smaller droplet size over the land than over the ocean. We confirm that the prediction of Asian monsoon activity is very sensitive to inclusions of aerosols and land-cloud enhancement. The control model, which uses the same cloud diagnosis scheme both over the land and over the ocean and does not include any effects of aerosols, systematically overpredicts the absorbed solar radiation (ASR) over land. The test model with these processes fairly reduces the systematic errors of land-ocean contrast of ASR. Over the Eurasian continent, the test model reduces ASR and lowers low-level temperature through land-atmosphere interactions. It suppresses monsoonal circulations in Southeast Asia and significantly delays northward migration of the typical fronts around East Asia, such as the Meiyu, Changma and Baiu fronts. The impact of land-cloud enhancement on one-month forecasts of the Asian monsoon seems to be similar to that of aerosols. Although the reduction of systematic errors of ASR indicates the relevance of the total effects of the two parameterization schemes, relative magnitudes of their impacts in nature are still uncertain. Further studies are required on distributions of aerosols and their optical properties, and cloud formation mechanisms particularly associated with the land-ocean difference, including aerosol-cloud interactions.

Jayaraman, K. S. (2002). "Climate model under fire as rains fail India." Nature [Nature] 418(6899).

As much of southern Asia faces its worst drought for 30 years, the Indian government is being heavily criticized for its reliance on a statistical model to forecast the monsoon. The India Meteorological Department (IMD), based in New Delhi, uses the model to issue a forecast of the monsoon every spring. This May it issued a prediction saying that rainfall would be 101% of normal. But by 6 August, this forecast remained way off the mark, with about three-quarters of the country having received very little rain.

Jeyaraman, S., S. Subramanian, et al. (1990). "Influence of weather parameters at the crop growth stages on seed yield of soybean." Mausam, New Delhi, India 41(4): 575-578.

Soybean is gaining importance in India. Identifying suitable soybean growing seasons necessitates for exploiting maximum yield potential in specific location. A time of sowing experiment with soybean var. Co. 1 was conducted to find the best time of sowing in summer and monsoon wet seasons at Tamil Nadu Agricultural University, Coimbatore. The influence of weather parameters prevailed during critical crop growth stages and whole cropping period on seed yield of soybean was studied. The production potential of soybean crop can be increased when grown in seasons having the maximum temperature of 31.2 degrees C to 31.6 degrees C, minimum temperature of 20.4 degrees C to 20. 9 degrees C, cumulative heat unit values of 1274 to 1292 and total bright sunshine hours of 383 to 456 for the whole cropping period.

Jiang, S., X. Yang, et al. (1993). "The characteristics of ``OLR'' for 1991 Mei-yu." Quarterly Journal of Applied Meteorology, Beijing, China 4(3): 301-309.

Using the mean pentad Outgoing Longwave Radiation (OLR) data observed from the NOAA satellites and the conventional weather observations for the 1991 Mei-yu season, a diagnostic study of the characteristics of the OLR is conducted. This paper describes the OLR and its anomaly patterns and the characteristics of propagation of the intraseasonal variation (ISV) of OLR during the 1991 flood Mei-yu periods. It is revealed that the variation of the ITCZ and the subtropical high are related to the evolution of the Mei-yu. The relationship between the anomalies of OLR over Tibet Plateau and the flood Mei-yu is also revealed. The results show that the earlier ITCZ occurrence in the western Pacific and the positive OLR anomalies (snow cover less than normal) over Tibet Plateau in winter are the important indications for the earlier onset date of the 1991 Mei-yu. Finally, by analyzing the features of the OLR pattern for the active and break phases of the 1991 Mei-yu and comparing with that of Indian monsoon, it is found that their onset dates are different from each other and their active phases either same or contrary. It is suggested that the complication of the Mei-yu in China is mainly due to the interaction between the middle latitude cold air and two kinds (east Asia and south Asia) of monsoon events.

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

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

Johri, A. P. and O. Prasad (1990). "Interaction of Southern Hemispheric Equatorial Trough with the southwest monsoon circulation during severe drought years." Mausam, New Delhi, India 41(4): 597-602.

The present study has further confirmed the inverse relationship between the intensity of the Southern Hemispheric Equatorial Trough (SHET) and the activity of the southwest monsoon over India. Continuous monitoring of weekly mean cloudiness in the zone of SHET may, therefore, serve as an useful tool in foreshadowing dry and wet spells of rainfall over India during the southwest monsoon.

Joseph, P. V. (1981). "Ocean-atmosphere interaction on a seasonal scale over north Indian Ocean and Indian monsoon rainfall and cyclone tracks: a preliminary study." Mausam, New Delhi 32(3): 237-246.

A preliminary study of synoptic sea surface temperature (SST) measurements made by ships plying over the north Indian Ocean has revealed the existence of an interesting ocean-atmosphere interaction. Large-scale monsoon failures over India during 1965 and 1966 caused an increase in SST in the Arabian Sea and Bay of Bengal. The warm seas may have been the cause of a persistent anticyclone that formed in the upper troposphere over the Indian seas immediately after the 1966 monsoon and persisted there until the monsoon of 1967, which was a normal monsoon. After this monsoon, SST over the Arabian Sea registered a fall. Conditions again became favorable for monsoon failure. Intensity of upwelling over the coastal waters of Somalia and Arabia (which is apparently regulated by the strength of the monsoon) is a factor with a major role in this interaction. These large-scale changes are found to affect the cyclone tracks also. This mechanism could, therefore, be the cause of the 3-yr oscillation in subtropical westerlies /tropical easterlies over south Asia, Indian monsoon rainfall, and tracks of the post monsoon severe cyclones of the Bay of Bengal observed during the decade 1965-1974 and reported by Joseph (1975, 1976). While in the sub-Saharan areas of Africa (like Sahel), there was a large rainfall deficit during every year from 1966 to 1974 (with the year 1972 having the largest deficit) in India, the generally bad monsoon decade 1965-1974 was broken by a normal monsoon once every 3 yr, i.e., 1967, 1970, and 1973. In the past, also, this area of Africa had similar long runs of dry spells (Kraus, 1977), but an examination of 100 yr of Indian rainfall shows that no interval between successive good monsoon years has exceeded 4 yr. This difference in African and Indian rainfall series must be due to the newly found ocean-atmosphere interaction occurring over the Arabian Sea and the Bay of Bengal.

Joseph, P. V. (1990). "Monsoon variability in relation to equatorial trough activity over Indian and West Pacific Oceans." Mausam, New Delhi, India 41(2): 291-296.

Variability of Indian monsoon rainfall has been examined in relation to the convective activity of the equatorial trough over the Indian Ocean and the Pacific Ocean west of the International Date Line. It is found that the cyclogenesis (tropical cyclones) near the West Pacific equatorial trough is closely related to this variability through a see-saw in convection between this ocean basin and the north Indian Ocean, with a period in the range of 30-50 days. SST anomalies over the north Indian Ocean and West Pacific Ocean can cause variability of the date of onset of monsoon and also the quantum of monsoon rainfall over India through the 30-50 day mode.

Jury, M. R. (1999). "Intra-seasonal convective variability over Southern Africa: principal component analysis of pentad outgoing-longwave radiation departures 1976-1994." Theoretical and Applied Climatology, Vienna, Austria 62(3-4): 133-146.

Intra-seasonal fluctuations of summer convection over southern Africa are studied through principal components (PC) analysis. Pentad (5 day) satellite outgoing long-wave radiation (OLR) departures are used to characterise the space and time scales of terrestrial cloudiness in the domain 10-35 degrees S, 10-40 degrees E. Areas of intra-seasonal convective influence are analysed according to spatial pattern and corresponding temporal character. Eight distinct geographic domains are identified, four tropical and four sub-tropical. The three most significant modes occur over southern Tanzania, Namibia, and Zambia, and refer to pulsing of the Indian NE monsoon, surface heating in the western desert, and the zonal ITCZ, respectively. Temporal characteristics vary widely but an underlying near-monthly rhythm is detected. The variety of modes suggests that convective weather systems respond to external forcing (wave trains) and internal dynamics, to produce intra-seasonal fluctuations over southern Africa.

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

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

Kandiannan, K., K. K. Chandaragiri, et al. (2002). "Crop-weather model for turmeric yield forecasting for Coimbatore district, Tamil Nadu, India." Agricultural and Forest Meteorology 112(3-4): 133-137.

Turmeric is native to India and its successful husbandry depends on the monsoon climate and the availability of irrigation. Yield forecasting in advance is required for export planning and policy decisions. A method to forecast turmeric yield from a time series of meteorological and yield data was developed and tested, using 20-year dataset of dry turmeric yield and monthly climatic variables for the crop's 9-month growing season. The variables, which had a significant correlation with yield were second month total rainfall (r = 0.60), third month mean evaporation (r = -0.49), fourth month mean wind speed (r = 0.61), fifth, eighth and ninth month mean minimum temperature (r = 0.45, 0.51 and 0.65, respectively) and ninth month mean minimum relative humidity (r = 0.66). Ten years (1979-1980 to 1988-1989) dataset were used for model building and remaining 10 years (1989-1990 to 1998-1999) data were used for testing the model. A multiple regression model was developed giving a forecast of the dry turmeric yield with a coefficient of determination of r super(2) = 89%.

Kau, W.-S. and B.-Y. Deng (1994). "The evolution of the south Asia upper anticyclone and the precipitation in early Mei-yu season." Atmospheric Sciences, Taiwan, Republic of China 22(1): 129-162.

In the early summer of south Asia, there are two major changes of large scale circulations: first is the beginning of the southeast Asia monsoon, which is also the beginning of the Taiwan Mei-yu season; and the second one is the onset of the India monsoon. The onset of the southeast Asia monsoon is often accompanied by a rapid northward movement of the upper level south Asia anticyclone (ULSAA) and an intensification of the low level southwesterly flow. With the use of the ECMWF grid points data from 1981 to 1986, we have analyzed the evolutions of the upper and lower level streamfunctions during the onset period of the Taiwan Mei-yu season. The result shows that the circulative domain of the ULSAA at 200 hPa can reach to Taiwan during its northward extension. At the same time the southwesterly flow from Indochina, which is passing through Taiwan to Japan, at 850 hPa is moving eastward along with the retreat of the Pacific subtropical high. Therefore, the upper level circulation brings the dry and cold air from the northwest and the low flow carries the wet and warm air from the southwest. Those two air masses merge together around the Taiwan area and provide favorable conditions for large scale convection. From the numerical simulations of the diabatic forcings to the ULSAA during the onset period of the Mei-yu season in 1984 and 1986 cases, we can find that: 1) the symmetric tropical convective heating could maintain the upper level anticyclone circulation on the tropics, 2) the convective heating over Indochina can intensify the upper level anticyclone circulation, and 3) the Tibetan sensible heating could cause the northward movement of the upper level anticyclone. We also find that the reactions of the ULSAA to the diabatic heating in different background flows will be different. If the large scale background flow is in anticyclone circulation then the ULSAA can be well maintained and intensified. However, if the background flow is in cyclone circulation then the ULSAA will be rapidly developed and moved toward west.

Kawamura, R. and T. Murakami (1998). "Baiu near Japan and its relation to summer monsoons over southeast Asia and the western North Pacific." Journal of the Meteorological Society of Japan, Tokyo, Japan 76(4): 619-639.

The slowly evolving annual cycle (signified as ``L-mode'') was defined by the sum of the first three sinusoids in a series of climatological pentad mean data of infrared equivalent black body temperature, 850 hPa wind, temperature, geopotential height and specific humidity, while the rapidly varying annual cycle (denoted by ``S-mode'') was determined by adding up the remaining sinusoids. During early summer, the L-mode exhibited a blocking-type configuration with a ridge over the Kamchatka-Okhotsk region, whereas a trough stretched eastward from northern China (center of a continental heat low) to Japan and beyond. The establishment of a locally independent L-mode anticyclonic cell over the Sea of Okhotsk enhanced low-level easterly anomalies from the vicinity of the Aleutian islands through northern Japan. The L-mode easterly anomalies merged with southwesterly anomalies along the southeastern periphery of a continental-scale heat low, thus generating a pronounced cyclonic shear zone around Japan accompanied by low-level moisture convergence. This L-mode lower tropospheric trough in intrinsically association with the east-west temperature gradient between East Asia and the western North Pacific plays a vital role in the formation of Baiu system in early summer. The L-mode southwesterlies along the east coast of China, which are attributed to the prominence of the continental-scale heat low, served as a bridge that links the monsoon westerlies of tropical origin with the westerly jet of mid-latitude origin. This resulted in producing a low-level westerly duct extending from the South China Sea to the central North Pacific. At the Baiu onset phase (mid-June), the S-mode onset cyclone of convective origin developed over the South China Sea, and concurrently the S-mode onset anticyclone organized to the northeast of the onset cyclone. The consolidated effect of these onset vortexes amplified in the vicinity of the low-level westerly duct was to cause the northward advection of warm and moist air from the tropics to southern Japan. By mid-July, the Asian continental heat low reached its peak and the summer monsoon over Southeast Asia became fully established. At the Baiu withdrawal phase (late July), the continental heat low began to decay because of land surface cooling; nevertheless, the L-mode Pacific High still developed northward and was most intense at the beginning of August. As the east-west temperature gradient between the ocean and continent decreased, the L-mode lower tropospheric trough near Japan dissipated, whereas L-mode WNPM (summer monsoon over the western North Pacific) trough prevailed in the subtropics. The withdrawal of Baiu was also characterized by the dominance of S-mode disturbances as well as the Baiu onset. It is thus anticipated that the seasonal evolution of L-mode circulation field, associated with continent-ocean thermal contrast, strongly regulates the activities of S-mode perturbations in and around the low-level westerly duct. It seems likely that the westerly duct served as a wave guide for the barotropic Rossby wave dispersion of the S-mode disturbances. The presence of horizontally sheared L-mode flow may also contribute substantially to the development and persistence of S-mode vortexes via in situ barotropic interaction process between the two modes. At any rate, the combined contribution of the L-mode flow and S-mode disturbances is to make such local climatological events as the onset and withdrawal of Baiu so rapid and dramatic.

Kawamura, T. (1986). "Regional division of winter weather and local winds in Japan." Japan. Tsukuba Univ., Institute of Geoscience, Science Reports, Sect. A, Geographical Sciences, Jan 7: 19-39.

The winter climate of Japan is strongly affected by the winter monsoon. It results in the cold temperature and heavy snow on the Japan Sea side and the cold, dry, and fine weather on the Pacific Ocean side of the Japanese Islands. The location of the weather divide is changed by the direction of airflow and the effect of topography. The purpose of this paper is to relate the regional division of weather and local winds to the winter monsoon. The distribution maps of the percentage frequency of precipitation amounts > 1, 5, 10, and 20 mm/day were made for each flow type decided by gradient wind direction at 850-mb level. To subdivide the climatic region with regard to weather, the following isolines of percentage frequency were noted: 10 and 90% in maps over 1, 5, ..., mm/day. Regional division by local wind was attempted. Especially, air speed of the local winds and locations of areas of strong or calm winds were clearly divided.

Keenan, T. D. (1988). "TRMM ground truth in a monsoon environment: Darwin, Australia." Australian Meteorological Magazine, Canberra 36(2): 81-90.

A ground truth station has been established at Darwin to provide data required for the Tropical Rainfall Measuring Mission of the National Aeronautics and Space Administration and the Tropical Oceans and Global Atmosphere (TOGA) project of the World Climate Research Programme. Darwin is situated in northern Australia in a monsoon environment typical of that experienced throughout the maritime continent of Southeast Asia. It will provide a monsoon data set to complement those data obtained already during the Global Atmospheric Research Programme Atlantic Tropical Experiment (GATE), Winter Monsoon Experiment, Australian Monsoon Experiment /Equatorial Mesoscale Experiment (EMEX), and the continuing TRMM data being collected at Kwajalein and Florida. The Darwin station consists of a National Oceanic and Atmospheric Administration (NOAA)/TOGA Doppler radar, full upper tropospheric soundings every 12 hr and wind soundings every 6 hr, and a mesoscale rain gage and surface-observing network operating in a continuous monitoring mode for the 1987-1988 and 1988-1989 summer monsoon seasons. Shorter special observing periods, which are the primary focus for the observation program, are providing rainfall and radar data sets comparable to those obtained during GATE. The climatological features of the Darwin site are described, together with examples of the large variety of oceanic and continental weather systems that occur. Spatial and temporal characteristics of rainfall occurring within the area are characterized by using radar data obtained during AMEX. Specific research objectives of the Bureau of Meteorology Research Centre are outlined.

Keenan, T. D. and L. R. Brody (1988). "Synoptic-scale modulation of convection during the Australian summer monsoon." Monthly Weather Review, Boston 116(1): 71-85.

Time-longitude representations of Japanese Geostationary Meteorology Satellite (GMS) IR imagery indicate the existence of major synoptic-scale banding of convection within the Australian summer monsoon. The bands can be interpreted as active and break phases of major convective activity within the monsoon. This study relates the occurrence of convection and its organization into synoptic-scale bands to observable flow features. GMS Digital Equivalent Blackbody Temperature (T sub(B) sub(B) ) data and wind fields from the Australian Numerical Meteorology Research Center (ANMRC) tropical analysis scheme for the 1978/1979 and 1983/1984 seasons were composited relative to wind field surges and bands of enhanced and suppressed convective activity. Some low-level wind surges in the South China Sea produced a modulation in the convective activity within the preexisting bands but did not seem to be associated with their formation. Surges in the Southern Hemisphere trade wind easterlies and the southerly jet off the west coast of Australia were not associated with any major change in convective activity. The organization of the convection into synoptic-scale bands was associated with the Southern Hemisphere 200-mb flow. Areas of enhanced convective banding were east of upper level tropospheric troughs. The troughs and associated subtropical jet streaks had amplified from the south, interacting and enhancing the monsoonal convection. West of the trough, in the region of subsiding air, the convection was suppressed. Independent studies taken from the 1984/1985 season showed that this type of interaction was discernible for individual cases.

Keenan, T. D., G. J. Holland, et al. (1987). "TRMM ground truth in a monsoon environment: Darwin, Australia." International Symposium on Tropical Precipitation Measurements, Tokai Univ., Tokyo, Japan, Oct.

The establishment of a TRMM ground truth station consisting of a Doppler radar and associated mesoscale rainfall network in the monsoon environment of the maritime continent of northern Australia is described. The aims are to provide a high-quality monsoon regime rainfall data set suitable for pre-TRMM studies and to undertake detailed case studies of the weather systems affecting northern Australia.

Keenan, T. D., G. J. Holland, et al. (1988). "TRMM ground truth in a monsoon environment: Darwin, Australia." Theon, John S. and Fugono, Nobuyoshi.

The establishment of a TRMM ground truth station consisting of a Doppler radar and associated mesoscale rainfall network in the monsoon environment of the ``maritime continent'' of northern Australia is described. The aims are to provide a high quality monsoon regime rainfall data set suitable for pre-TRMM studies and to undertake detailed case studies of the weather systems affecting northern Australia.

Kerr, R. A. (1988). "Weather in the wake of El Nino." Science, Wash., D.C. 240(4854).

The episode that began officially in 1986 ended this March as the warmer than normal waters of the equatorial Pacific faded. This El Nino did everything from drying out India by weakening the monsoon to warming an already overheating globe. It was found that the timing and amplitude of each stage of an ENSO event are too variable for simple classification. As this ENSO event faded, so did its effects on the weather around the globe. The year 1987 was the warmest, on average around the globe, in the 100-yr record of instrumentally recorded temperatures.

Keshavamurty, R. N. and S. T. Awade (1974). "Dynamical abnormalities associated with drought in the Asiatic summer monsoon." Indian Journal of Meteorology and Geophysics, Delhi 25(2): 257-264.

The years 1965 and 1972 were years of severe drought over India and its surrounding area. The dynamical and thermal features of these seasons are contrasted with those of the normal monsoon. The main local abnormality during drought years is the shift of the monsoon trough northwards and the development of anticyclones over central India in the lower troposphere. The main abnormality in the thermal field is that temperatures are considerably below normal over southern parts of the U.S.S.R., Iran, Afghanistan, and north India. Quasi-geostrophic ` omega ' is used to delineate the vertical circulations. It is seen that the N-S circulation and associated energy conversion is weaker and the E-W circulation, more marked during breaks. A model of the vertical circulations during drought periods is suggested. The intensity, phase, movement, and vertical and horizontal tilts of the different wavenumbers in the midlatitudes during drought and in the preceding months is contrasted with the normal. In 1972, wavenumbers 5-9 were abnormally pronounced and showed some dynamical differences.

Khambete, N. N. and B. C. Biswas (1984). "Application of Markov chain model in determining drought proneness." Mausam, New Delhi 35(3): 407-410.

A rainfall distribution, especially a run of wet and dry spells, has a dominant effect on the crop yield. A two-state Markov chain model of order one is used to evaluate sequences of dry and wet weeks during the southwest monsoon period over a dry farming region of Maharashtra. An index based on parameters of this model has been developed to bring out the degree of drought proneness. By using this index, the dry farming tract of Maharashtra is delineated into five zones according to degree of drought proneness.

Khole, M. and U. S. De (1999). "Floods and droughts in association with cold and warm ENSO events and related circulation features." Mausam [Mausam] 50(4).

For the Indian subcontinent, the occurrence of floods and droughts is closely linked with the summer monsoon activity. The phenomenon of E1 Nino-Southern Oscillation (ENSO) has been established to be one of the major teleconnections of Indian Summer Monsoon. Also the relationship between the circulation features and summer monsoon activity is well documented in the literature. The interaction of ENSO with monsoon system was known to the seasonal forecasters in India from the days of G. Walker. Normand (1953) summarising these results has remarked that `Monsoon has a prolonged influence on the global weather rather than global weather parameters influencing the monsoon'. 1990-94 was a prolonged period of warm ENSO producing weather anomalies in different regions of the globe. Yet during the same period all India rainfall was very close to normal and in fact, 1994 was a year of abundant rainfall for India. The aim of the study is to examine some of these features more critically. It is observed that ENSO has a modifying effect on the regional scale circulation pattern and possible interactions and/or phase-locking with the planetary scale circulation pattern, which results into the occurrence or non-occurrence of an extreme event. Also, a qualitative analysis is carried for a period 1960-90 to assess how far the mid-season rainfall deficiency is made up at the end of the season. It is observed that even during drought years, the mid-season rainfall deficiency is made up at the end of the season for a considerable percentage of the total number of cases.

Khole, M. and U. S. De (2001). "Floods and droughts in association with cold and warm ENSO events and related circulation features." Mausam [Mausam] 1: 13-24.

For the Indian subcontinent, the occurrence of floods and droughts is closely linked with the summer monsoon activity. The phenomenon of E1 Nino-Southern Oscillation (ENSO) has been established to be one of the major teleconnections of Indian Summer Monsoon. Also the relationship between the circulation features and summer monsoon activity is well documented in the literature. The interaction of ENSO with monsoon system was known to the seasonal forecasters in India from the days of G. Walker. Normand (1953) summarising these results has remarked that `Monsoon has a prolonged period of warm ENSO producing weather anomalies in different regions of the globe. Yet during the same period all India rainfall was very close to normal and in fact, 1994 was a year of abundant rainfall for India. The aim of the study is to examine some of these features more critically. It is observed that ENSO has a modifying effect on the regional scale circulation pattern and possible interactions and/or phase-locking with the planetary scale circulation pattern, which results into the occurrence or non-occurrence of an extreme event. Also, a qualitative analysis is carried for a period 1960- 90 to assess how far the mid-season rainfall deficiency is made up at the end of the season. It is observed that even during drought years, the mid-season rainfall deficiency is made up at the end of the season for a considerable percentage of the total number of cases.

Kingston, G. J. (1987). "Tropical circulation in the Australian/Asian sector: April to Sept. 1986." Australian Meteorological Magazine, Canberra 35(1): 1-17.

A synoptic analysis is presented concerning the tropical circulation between the longitudes 70 degrees and 180 degrees E for the Southern Hemisphere winter of 1986. From data analyzed, it is inferred that, during this perod, the tropical Hadley cells were weaker than normal with their foci of ascent and descent displaced eastward from the climatologically normal positions. The changed large-scale circulation was associated with significant variations in regional climate: central Australia experienced record wintertime rains; a 28-yr minimum in tropical cyclone numbers was observed in the northwest Pacific Ocean, and the rainfall over the Indian subcontinent was below normal for the southwest monsoon season.

Krishna Rao, D. (1982). "Karnataka weather guide, in maps." Mysore, India 13.

Climatological features of Karnataka, (India) are presented in maps, according to month. The two main maps in each month show lines of equal rainfall and details of rainy days, temperature, and humidity at selected places. Each map is self explanatory. Background information is given on small maps of India showing mean sea level isobars (pressure) and direction of prevailing winds for different months. Special maps show the normal dates of onset and withdrawal of southwest and northeast monsoon and the normal tracks of storms affecting Karnataka for the appropriate months. Salient weather features of Karnataka in each month are also mentioned. All of the maps have been prepared by using long-term averages and, as such, this weather guide could be considered as reference material. For daily and special weather forecasts, however, daily weather bulletins, prepared by using synoptic weather maps, weather radar, and satellite pictures broadcast by All-India Radio Stations, Doordarshan (TV), and published in newspapers, should be consulted. The Main Meteorological Office at Bangalore Aerodrome handles all weather enquiries pertaining to Karnataka State.

Krishnamurti, T. N. (1975). "Study of a monsoon depression, Pt. 1, Synoptic structure." Florida. State Univ., Tallahassee. Dept. of Meteorology, Report(75).

This is an observational study of a monsoon depression during its westward passage across India. A study is presented based on available conventional radiosonde, rawinsonde pilot balloon, and commercial aircraft wind reports during Aug., 1968. Besides showing conventional analysis of the motion and thermal fields, the authors also show vertical structure diagrams. The important findings of the observational study are that the horizontal scale of the depression is about 2000 km; the vertical scale, about 10 km; and its westward speed of motion, about 5 degrees long./day. The monsoon depression is an intense closed vortex that has horizontal wind speeds of about 10 to 15 m.p.s., and its closed circulation extends to about 9 km in the vertical. A narrow vertical tube of cyclonic vorticity with a horizontal scale identical with 1000 km and extending to 9 km is a characteristic feature of this circulation. This depression formed over the northern part of the Bay of Bengal and dissipated over the Arabian Sea. The vortex has a well defined cold core in the lower troposphere and a warm core above 500 mb. To the west of the cold core, there exists an intense warm core in the lower troposphere, which is a consequence of advection of desert air by the storm circulation. Vertical motions show rising motion west of (i.e., ahead of) the trough line, and a descending motion to the rear. The westward motion of the monsoon depression is related to intense low level convergence in the region of the strongest ascending motion. In this region, rainfall rates exceed 10 cm/24 hr during the passage of the disturbance. The analysis and observational structure derived in this study are examined in a second part of this paper, in which the dynamics, energetics, and numerical prediction aspects are stressed.

Krishnamurti, T. N. (1984). "Numerical weather prediction in low latitudes." National Workshop on the Global Weather Experiment: Current Achievements and Future Directions, 1st, Woods Hole, MA., July 2: 163-187.

The observation sequence during the onset of the monsoon over the Indian subcontinent in the year of the Global Experiment was found to have the following scenario: as the heat sources commence a rapid northwestward movement toward the southeastern edge of the Tibetan Plateau, there is a configuration of the large-scale divergent circulation favoring the development of a rapid exchange of energy from divergent to rotational kinetic energy. This observational sequence was tested by a series of short-range prediction experiments that differed from each other in the definition of initial heat sources. The differential heating between the Arabian Sea and the southeastern edge of the Tibetan Plateau is described by a net cooling over the ocean (domination by radiative forcing) and strong net heating over the Himalayas (dominated by convective forcing). This strong heating occurs over regions of organized cumulus convection where a large moisture supply is available. In order to provide such a forcing in the different initial states for the proposed experiments, the divergent wind and the humidity were extracted from three different epochs in the monsoon evolution: springtime, preonset, and postonset. The rotational wind, pressure, and temperature fields were kept identically the same in all of the experiments. Since the divergent wind and humidity fields differed in each case, the application of a cumulus parameterization scheme that depended upon moisture convergence gave rise to different measures of latent heating initially. The physical initialization, which aims toward reasonable rainfall roles in the rainy areas and an advective-radiative balance elsewhere, is described. The cumulus parameterization is set forth. Two recent studies on tropical cyclogenesis conducted with the global model and constituting real-data forecast on the medium-scale-range time frame are presented.

Krishnamurti, T. N. (1985). "Divergent circulations on the 30- to 50-day time scale." Journal of the Atmospheric Sciences, Boston 42(4): 364-375.

A review of the recent results on the 30-50-day time scale is presented. The authors examine the divergent circulations on the time scale of 30-50 days during the FGGE year. This study is based on two different data sets: the FGGE 3b analysis from the European Center for Medium Range Weather Forecasts (ECMWF), and the Florida State University analysis of the circulation over the monsoon region during the FGGE year. The analysis identifies a planetary-scale divergence wave that traverses around the globe eastward throughout the FGGE year. Its speed of eastward propagation is similar to 8 degrees long. day super(-) super(1) . The amplitude of this wave is largest during the summer season over the monsoon region and the western Pacific Ocean. The amplitude decreases as the wave traverses across the eastern Pacific and Atlantic oceans. This wave appears to modulate the monsoon activity so that active and inactive spells seem to bear a close relationship to the divergence on this time scale. A planetary-scale sea level pressure wave accompanies this divergence wave and is also presented. The regional higher density data shows a meridionally propagating divergence wave that moves from the equatorial latitudes toward the Himalayas in the monsoon region. The two sets of analysis (global and regional) clarify this dichotomy concerning the zonal vs. the meridional phase propagation of the divergent circulations on this time scale. Another aspect relates to the phase locking of two families of low-frequency waves during the breaks (inactive spells) of the monsoon. Besides the eastward propagating planetary-scale waves on the 30-50-day time scale, a 10-20-day westward propagating wave has been noted to influence the monsoon activity. The simultaneous arrival of ridges (or high pressure) of these two families of low-frequency waves during breaks is an interesting phase-locking phenomenon. Similar phase locking of troughs of sea level pressure are noted during the active spells of monsoon. With regard to the energetics on this time scale, it is questioned whether the 30-50-day divergent circulations are thermally direct. Calculations performed in a frequency domain confirm the thermally direct circulation.

Krishnamurti, T. N., H. S. Bedi, et al. (1993). "Hurricane forecasts in the FSU models." Advances in Atmospheric Sciences, Beijing, China 10(1): 121-132.

A brief account of our studies on the hurricane forecast problem is presented here. This covers recent prediction results from the Florida State University (FSU) regional and global numerical weather prediction models. The regions covered are the Indian and the Pacific Oceans. The life cycle of the onset vortex (a hurricane) of the summer monsoon, typhoons over the western Pacific Ocean and tropical cyclones over the Bay of Bengal (Andhra Pradesh and the Bangladesh storms) are covered here. The essential elements in the storm formation are the strong horizontal shear in the cyclogenetic areas, a lack of vertical shear and warm sea surface temperatures. The storm motion has a steering component largely described by the advection of vorticity by a vertically averaged layer mean wind, the recurvature of a storm appears to invoke physical processes via the advection of divergence by the divergent part of the wind especially in the outflow layers of the storm. Very high resolution global models seem to be able to handle the motion and structure during the entire life of typhoons quite reasonably. The scope for better diagnosis of the storms life cycle appears very promising in view of the realistic simulation of the life cycle.

Krishnan, R., C. Venkatesan, et al. (1998). "Dynamics of upper tropospheric stationary wave anomalies induced by ENSO during the northern summer: a GCM study." Proceedings of the Indian Academy of Sciences, Bangalore, India 107(1): 65-90.

Ensemble seasonal integrations are carried out with the COLA GCM, with a view to understand the dynamical connection between warm SST anomalies in the equatorial central-eastern Pacific Ocean and the upper level stationary wave anomalies seen during drought years over the Indian summer monsoon region. In addition, experiments with and without orography are performed in order to examine the role of the Himalayas in modulating the El Nino induced stationary wave anomalies over the summer monsoon region. The GCM simulations show a statistically significant weakening of the summer monsoon activity over India in response to the SST forcing in the equatorial Pacific Ocean. This weakening of the summer monsoon appears to be largely related to modifications of the local Hadley and Walker cells over the summer monsoon region. In addition, it is seen that the anomalous ENSO divergent forcing over the tropical Pacific Ocean can act as a potential source for Rossby wave dispersion. Here one finds the possibility of meridionally propagating Rossby waves, which emanate from the ENSO forcing region, to interact with the subtropical westerlies and generate anomalous highs and lows in the subtropics and extratropics. The quasi-stationary perturbations seen over west Asia, Pakistan and northwest India during drought years, seem to be generated by the above mechanism. An alternate mechanism that could be important for the persistence of the quasi-stationary perturbations seems to be based on the dynamic excitation of middle latitude normal modes which can extract energy from the zonally varying unstable basic flow. It is seen from the GCM simulations, that the Himalayan orography plays a crucial role in anchoring the El Nino induced extratropical westerly troughs far to the west in the high latitude belt. In the absence of orography it is seen that the ENSO induced extra-tropical cyclonic anomalies tend to intrude southward into the monsoon region thereby destroying the regional scale circulations completely. Another effect due to the Himalayas is to generate lee waves on the eastern side of the topographic barrier which encircle the globe in the subtropics and midlatitudes.

Kulkarni, P. L. (1985). "Release of kinetic energy by the meridional circulation during the development of a depression over Bay of Bengal." National Seminar cum Workshop on Atmospheric Science and Engineering, Calcutta, India, Feb.

The strength of the cyclones, anticyclones, and other systems forming the weather pattern are often measured in terms of their kinetic energy. Intensifying and weakening systems are regarded as those gaining or losing kinetic energy. Quantitative estimates of the releases of kinetic energy by the meridional circulation from 1000 to 100 mb over the Indian region during the development of the depression from July 5 to 8, 1979, over the Bay of Bengal are made. Results show that on July 5 and 6, there was consumption of kinetic energy, whereas on July 7 and 8, there was production of energy. Maximum consumption occurred on July 5, when the monsoon was weak over the country, whereas maximum production occurred on July 7, at similar to 20-24 degrees N, when the depression was intensifying.

Kumar, A., P. Maini, et al. (2000). "An operational medium range local weather forecasting system developed in India." International Journal of Climatology, Chichester, UK 20(1): 73-87.

A forecasting system for objective medium range location specific forecasts of surface weather elements was evolved at the National Centre for Medium Range Weather Forecasting (NCMRWF). The basic information used for this is the output from a general circulation model (GCM). The two essential components of the system are statistical interpretation (SI) forecast and direct model output (DMO) forecast. These are explained in brief. The SI forecast is obtained by using dynamical-statistical methods like model output statistics (MOS) and the perfect prog method (PPM) in which prediction of upper air circulation from a GCM around the location of interest is used. The DMO forecast is obtained from the prediction of surface weather elements from the GCM. The procedure for preparation of final forecast by using these two components and prevailing synoptic conditions is also explained. This is essentially a man-machine-mix approach. Finally, an evaluation of the forecast skill for the 1996 monsoon and some of the future plans are presented.

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.

Kumar, J. R. and S. K. Dash (1999). "Inter-annual and intra-seasonal variation of some characteristics of monsoon disturbances formed over the Bay." Mausam 50(1): 55-62.

The characteristics of monsoon disturbances during drought and flood years for the period 1971-96 are studied to find out their inter-annual variations. Variations of some of the characteristics of monsoon disturbances formed over Bay during 1979-88, with respect to different monsoon conditions such as strong, weak and break monsoons, are also studied. The results show that monsoon disturbance days are higher during flood years than during drought years. Drought years are associated with higher chances of low pressure areas to intensity into depressions, less westward movement, more horizontal extent, intense pressure departure from normal in comparison with flood years. However, more monsoon disturbances tilt significantly during flood years. The rainfall associated with these disturbances is highly variable and does not depend on the intensity, horizontal and vertical extent of the individual system. More number of lows intensify into depressions during storng monsoon conditions compared to those of weak monsoon conditions. Lows and depressions during strong monsoons have more westward movement and longer life period. Generally, very few lows form during break monsoon and none of them intensify into depression. Hence, the presence of mid-tropospheric heating during strong and weak monsoons is essential for the formation of depression. Synoptic systems which abate break monsoon condition and re-establish normal monsoon are also discussed.

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

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

Kumar, S., T. Prasad, et al. (1999). "A synoptic-climatic study of the onset of southwest monsoon over Mumbai." Proceedings of the Indian Academy of Sciences, Bangalore, India 108(4): 321-326.

Surface and upper air synoptic features prevailing at the time of onset of southwest monsoon over Mumbai have been examined for a period of 50 years from 1947 to 1996. These synoptic situations have been found to fall under three broad categories. The study shows that on about 66% of the occasions, the onset of monsoon over Mumbai is caused by low pressure area forming over southeast and east central Arabian Sea as they move northwards, while on 28% of the occasions, the onset is due to the low pressure systems forming over northwest/head Bay of Bengal and their movement towards northwest/west northwest. Based on the findings of the study and the climatological aspects, a criterion for declaring onset over Mumbai has been suggested.

Kuo, Y.-H., L. Cheng, et al. (1986). "Mesoscale analyses of the Sichuan flood catastrophe, 11-15 July 1981." Monthly Weather Review, Boston 114(11): 1984-2003.

During the period July 11-15, 1981, heavy rainfall occurred over the Sichuan basin in China, resulting in severe floods that took a large toll in human life and property damage. Synoptic analyses indicate that, early in this period, the southerly monsoon flow was particularly strong near the basin because of a favorable positioning of the Pacific subtropical high and the Indian monsoon depression. The passage of a deep midlatitude trough from the Lake Baikal region brought colder, drier air from Siberia into southwest China. The Siberian air stream met the monsoon current over the eastern plateau and the Sichuan basin, creating a region of large-scale, low-level convergence. Mesoscale analyses show that the flood was directly related to the extreme development of a long-lived mesoscale vortex (called the southwest (SW) vortex by Chinese meteorologists) over the basin as it merged with another mesoscale vortex generated over the Tibetan Plateau. Mesoscale heat and moisture budgets suggest that the latent heat release associated with cumulus convection contributed substantially to the development of the SW vortex. It is found that heating resulting from convective eddy flux convergence of sensible and latent heat is about half the amount of latent heat release resulting from condensation. Moisture flux analyses and isentropic trajectories indicate that the major moisture source for the flood was from the Bay of Bengal. This moisture was transported over (and around) the southeastern corner of the Tibetan Plateau to the basin. The SW vortex finally dissipated after the passage of a surface cold front associated with the Lake Baikal trough. The authors hypothesize that the formation of the SW vortex was a consequence of the blocking of the southwesterly monsoon flow by the mesoscale mountain range (located at the southeastern corner of the Tibetan Plateau). This is suggested by the fact that the SW vortex was initiated completely within this southwesterly monsoon current, that it was strongest at the lower levels during its formation stage, and that the low-level cyclonic vorticity was present throughout the period that the southwesterly monsoon flowed around the plateau.

Kurbet, A. S. (1989). "Synoptic situations associated with spells of strong and weak monsoon over Madhya Maharashtra." Mausam, New Delhi 40(2): 225-227.

The synoptic situation with the unusual heavy rainfall during Aug. 1969 reported in Madhya Maharashtra is examined. The Aug. 1969 rainfall was among the top two or three rainiest Augusts recorded during the 75 yr of 1901-1975. Rainfall was in excess of normal in nearly three fourths of the region, and by >200% in one fourth of the region. It is shown that, although on most of the occasions of the passage of surface or upper air flows across the South Peninsula during break monsoon conditions, rainfall is scanty in Madhya Maharashtra, on the rare occasions when the upper air cyclonic circulation associated with the system extends to Madhya Maharashtra, the region may get a spell of vigorous monsoon.

Kurihara, K., N. Davidson, et al. (1996). "Simulations of tropical cyclone Connie from the Australian Monsoon Experiment." Australian Meteorological Magazine, Canberra, Australia 45(2): 101-111.

Simulations have been made of tropical cyclone Connie which developed during the Australian Monsoon Experiment (AMEX) Phase 2. The aims are to investigate factors which affected the cyclone's movement. Experiments were made using a primitive equation model with parameterised physical processes, which has been developed at JMA (Japan Meteorological Agency). Reprocessed objective analyses from the European Centre for Medium Range Weather Forecasts (ECMWF), and the JMA's typhoon implantation scheme were used to generate the initial conditions. Analysis of the vorticity equation using data from the 24-hour simulations shows that the horizontal advection of absolute vorticity and the divergence term were dominant effects on the motion. This suggests that the track was determined by (a) steering flow, (b) the beta effect and (c) lower layer convergence which was generated and intensified by parameterised condensational heating. With regard to the beta effect, we illustrate that the motion in the three-dimensional atmosphere had similar characteristics to the motion of a vortex in a nondivergent barotropic flow. That is, the track was sensitive to tropical cyclone size, but insensitive to its inner core structure. Further, the track differences simulated from initial data containing circulations of different size became larger with simulation time. We conclude that to a first approximation, tropical cyclone Connie moved in a similar way to a vortex in a nondivergent barotropic flow, but its movement was modified by condensational heating.

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

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

Lam, K. S., T. J. Wang, et al. (2001). "Flow patterns influencing the seasonal behavior of surface ozone and carbon monoxide at a coastal site near Hong Kong." Atmospheric Environment, Oxford, England 35(18): 3121-3135.

Surface O sub(3) and CO were measured at Cape D'Aguilar, Hong Kong during the period of January 1994 to December 1996 in order to understand the temporal variations of surface O sub(3) and CO in East Asia-West Pacific region. The isentropic backward trajectories were used to isolate different air masses reaching the site and to analyze the long-range transport and photochemical buildup of O sub(3) on a regional scale. The results show that the diurnal variation of surface O sub(3) was significant in all seasons with daily O sub(3) production being about 20 ppbv in fall and 10 ppbv in winter, indicating more active photochemical processes in the subtropical region. The distinct seasonal cycles of O sub(3) and CO were found with a summer minimum (16 ppbv)-fall maximum (41 ppbv) for O sub(3) and a summer minimum (116 ppbv)-winter maximum (489 ppbv) for CO. The isentropic backward trajectory cluster analyses suggest that the air masses (associated with regional characteristics) to the site can be categorized into five groups, which are governed by the movement of synoptic weather systems under the influence of the Asian monsoon. For marine-originated air masses (M-SW, M-SE and M-E, standing for marine-southwest, marine-southeast and marine-east, respectively) which always appear in summer and spring, the surface O sub(3) and CO have relatively lower mixing ratios (18, 16 and 30 ppbv for O sub(3) , 127, 134 and 213 ppbv for CO), while the continental air masses (C-E and C-N, standing for continent-east and continent-north, respectively) usually arrive at the site in winter and fall seasons with higher O sub(3) (43 and 48 ppbv) and CO (286 and 329 ppbv). The 43 ppbv O sub(3) and 286 ppbv CO are respresentative of the regionally polluted continental outflow air mass due to the anthropogenic activity in East Asia, while 17 ppbv O sub(3) and 131 ppbv CO can be considered as the signature of the approximately clean marine background of South China Sea. The very high CO values (461-508 ppbv) during winter indicate that the long-range transport of air pollutants from China continent is important at the monitoring site. The fall maximum (35-46 ppbv) of surface O sub(3) was believed to be caused by the effects of the weak slowly moving high-pressure systems which underlie favorable photochemical production conditions and the long-range transport of aged air masses with higher O sub(3) and its precursors.

Lamb, H. H. (1977). "Some comments on the drought in recent years in the Sahel-Ethiopian zone of North Africa." Dalby, David 2: 33-37.

The author examines the changes in atmospheric pressure and the simultaneous changes in wind motions which occurred from the 1950s to the end of the 1960s and which produced the prolonged rainfall deficit in the zone immediately south of the Sahara and comprising the Sahel and Ethiopia. Corresponding changes occurred in middle and high latitudes of both hemispheres. It appears that this precipitation deficit phenomenon developed over a period that already encompasses 30 yr; the short-term climatic fluctuations, including those that occurred in Ethiopia and seem to be associated with the 11-yr sun-spot cycle, apparently play only a secondary role compared to the long-term changes. The direct causes of the increase in the frequency of drought in the Sahel-Ethiopia zone during recent years appear to be changes in the atmospheric currents over long stretches of the Earth (over Europe, Asia, and North Africa) and a simultaneous northward penetration of weaker atmospheric flows of the monsoon. Conversely, precipitation has increased during the past 15 yr in zones of Africa which are nearer the Equator and in zones of East Africa immediately south of the Equator; lake levels in these regions are higher than those recorded in the preceding period.

Lander, M. A. (1994). "Description of a monsoon gyre and its effects on the tropical cyclones in the western North Pacific during August 1991." Weather and Forecasting, Boston, MA 9(4): 640-654.

This paper describes the character and evolution of the low-level wind, sea level pressure, and satellite-observed cloudiness over the western North Pacific (WNP) during August 1991 when the low-level monsoon circulation there became organized as a monsoon gyre. The specific configuration of the monsoon circulation, which herein is called a monsoon gyre, is an episodic event--occurring roughly once per year, for two or three weeks during July, August, or September. As a monsoon gyre, the low-level circulation of the WNP becomes organized as a large cyclonic vortex associated with a nearly circular 2500-km-wide depression in the contours of the sea level pressure. A cyclonically curved band of deep convective clouds rims the southern through eastern periphery of this large vortex. Once this pattern is established, it becomes a prolific generator of mesoscale vortices that emerge from the downstream end of the major peripheral cloud band. These mesoscale vortices form the seed disturbances for midget or small-sized tropical cyclones. The large area encompassed by the outermost closed isobar of the monsoon gyre of August 1991 (the centroid of which moved slowly westward along 20 degrees N) was the site of genesis for two tropical depressions, two tropical storms, and two typhoons during its 20-day westward journey, Initially, small tropical cyclones formed in the peripheral circulation of the gyre and later, the gyre itself evolved into a very large tropical cyclone; this is suggestive of two distinct modes of tropical cyclogenesis: one mode operates to produce small tropical cyclones in the eastern periphery of the gyre, and the other mode operates to accelerate the winds of the monsoon gyre until it becomes a giant tropical cyclone.

Lander, M. A. (1996). "Specific tropical cyclone track types and unusual tropical cyclone motions associated with a reverse-oriented monsoon trough in the western North Pacific." Weather and Forecasting, Boston, MA 11(2): 170-186.

In its simplest description, the large-scale low-level circulation of summer over the western North Pacific Ocean can be described in terms of low-latitude southwesterlies, a monsoon trough, and a subtropical ridge. When the axis of the monsoon trough is in its normal orientation (NW-SE), tropical cyclones tend to move northwestward on tracks close to those expected from climatology. As an episodic event, the axis of the monsoon trough extends farther north and east than normal and acquires a reverse (SW-NE) orientation. When the monsoon trough becomes reverse oriented, tropical cyclones within it tend to exhibit north-oriented motion and other specific unusual motions such as eastward motion at low latitude and binary interactions with other tropical cyclones along the trough axis. Approximately 80% of the tropical cyclones that are associated with a reverse-oriented monsoon trough move on north-oriented tracks. A tropical cyclone track type, defined herein as the ``S''-shaped track, is primarily associated with reverse orientation of the monsoon trough: 23 of 35 cases (66%) of S motion during the period 1978-94 occurred in association with a well-defined reverse-oriented monsoon trough.

Lander, M. A. (1999). "A tropical cyclone with a very large eye." Pictures of the month Monthly Weather Review, Boston, MA 127(1): 137-142.

Some typhoons that form in the monsoon trough of the western North Pacific generate circulations and eyes at the large end of the global size distribution. The 370 km diameter of Winnie's outer eyewall cloud when it passed over Okinawa is one of the largest ever observed in a TC. These cases are important because they define the extreme possibilities for TC dynamics. Attributes of super typhoon Winnie, in particular the eye, are related in this article using text, figures, and satellite images.

Lander, M. A. (1999). "A tropical cyclone with an enormous central cold cover." Pictures of the month Monthly Weather Review, Boston, MA 127(1): 132-136.

During late July 1996 the tropical atmosphere of the western North Pacific was dominated by an active monsoon trough. On 23 July, three TCs were developing along the axis of this trough: Frankie (in the South China Sea), Gloria (in the Philippine Sea, east of Luzon), and Herb (northeast of Guam). Gloria had been developing as a monsoon depression, defined by the Joint Typhoon Warning Center (JTWC) as a large (but relatively weak) cyclone in the monsoon trough that is composed of an ensemble of mesoscale convective systems (MCSs) (JTWC 1993). During the evening hours of 23 July, a cluster of small cold-topped MCSs began to grow near the estimated center position of Gloria. During a 6-h period, this cluster of MCSs mushroomed into an enormous CCC. By local midnight, the average diameter of the area within which the cloud-top temperature was at or below -70 degrees C was approximately 780 km. In relation to published statistics of convective cloud sizes, Gloria's CCC is extraordinarily large. The area of that portion of Gloria's CCC that is colder than -70 degrees C is nearly 500 000 km super(2) .

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

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

Lau, K. M. and 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.

Lazic, L. (1990). "Forecasts of AMEX tropical cyclones with a step-mountain model." Australian Meteorological Magazine, Canberra, Australia 38(3): 207-216.

The numerical forecasts of tropical cyclones, which occurred during the AMEX (Australian Monsoon Experiment), have been studied. The UB /NMC (University of Belgrade/National Meteorological Center, Washington) limited area model, with vertical coordinate which permits a step-like representation of mountains and quasi-horizontal coordinate surfaces (so-called eta coordinate), was used. The physical package includes Mellor-Yamada level 2.5 turbulent exchange with level 2 used in the lowermost layer, large-scale precipitation and evaporation, Betts-Miller convective parameterization, surface processes after Miyakoda and Sirutis, and the NMC version of the GLA (Goddard Laboratory for Atmospheres) radiation scheme. The model was run with 0.5 degrees x 0.5 degrees horizontal resolution and 16 layers in the vertical. The realistic 48-hour forecasts of AMEX tropical cyclones (Connie, Irma, Damien and Jason) based on ECMWF (European Centre for Medium Range Weather Forecasts) operational analyses, that is real-time data (without additional AMEX data available in delayed mode) for initial and forecasts for boundary data, demonstrate the model's ability to predict tropical cyclones.

Lazic, L. (1993). "Eta model forecasts of tropical cyclones from Australian monsoon experiment: dynamical adjustment of initial conditions." Meteorology and Atmospheric Physics, Vienna, Austria 52(3-4): 101-111.

The University of Belgrade/National Meteorological Centre, Washington (UB/NMC) limited area Eta Model predicted the development, structure, associated precipitation and tracks of the Australian Monsoon Experiment (AMEX) (10 January through 15 February 1987) tropical cyclones Connie, Irma, Damien and Jason. The initial positions and intensities of the tropical cyclone vortices from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, which are used as initial data, do not quite agree with the observations. These disagreements produce additional errors in predicting the tropical cyclone tracks. To improve the initial position of the vortex, the flow is split into the small and the large scale motions, and during the first two hours of the integration, the small-scale part is forced in small steps towards its observed position. The adjustment is performed with the reduced model dynamics (adjustment processes only) and no physics. With the adjustment during the first two hours of the integration, the model successfully adjusts to the new position of the initial vortex. After the completion of the adjustment stage, the model runs normally, i.e., without any modification. The tracks of the 48-h forecasts with the adjusted initial vortices are parallel to the tracks obtained in the control forecasts without the adjustment. However, e.g., the mean absolute error of the positions during 48-h forecast of the tropical cyclone Connie was reduced from 174 km in the control case to 129 km in the case with adjustment of the position. The latent heat, the thermal energy, the kinetic energy and the total energy of the extracted small scale vortices are calculated every three hours of the integration time. These small-scale energies obtained in the 48-h control forecast are compared to those of the run with the initial vortex adjustment to monitor the ``spin-up'' of the model.

Lazic, L. (1993). "Eta model forecasts of tropical cyclones from Australian monsoon experiment: the model sensitivity." Meteorology and Atmospheric Physics, Vienna, Austria 52(3-4): 113-127.

The Australian Monsoon Experiment (AMEX) (10 January through 15 February 1987) has resulted in the first ever quality mesoscale data set in the Australian tropics. This provides the first observational confirmation of previous hypotheses, modelling experiments and refinement of the parameterization of convective processes. During the AMEX a large area of convective activity off northwestern Australia accompanied four tropical cyclones onset: Connie, Irma, Damien and Jason. As already reported by the author, the Eta Model of the University of Belgrade and the National Meteorological Centre, Washington (UB/NMC), successfully predicted the development, structure, associated precipitation and tracks of these cyclones. Using again the AMEX tropical cyclone cases, in the present study the sensitivity of the Eta Model is examined with respect to the initial and boundary conditions, the vertical coordinate and orography, the location of the initial vortex, the surface fluxes of heat and moisture, the sea surface temperature and the Betts-Miller convection parameterization scheme. Also, some available forecasts of the AMEX tropical cyclones were intercompared. These included the forecasts obtained by the Eta Model, the T106 global (then) operational European Centre for Medium-range Weather Forecasts (ECMWF) model, the ECMWF T106 limited area model and the Florida State University (FSU) limited area model. A review of the intercomparison results suggests that the Eta Model is highly competitive with the other sophisticated models, both in terms of quality and the computational effort required.

Le Comte, D. (1981). "Rains, floods, and cold: international weather in 1980." Weatherwise, Wash., D.C 34(1): 13-15.

For most Americans, the outstanding weather event of 1980 was the severe heat wave and drought; Mexico, Canada, and large areas of southern Australia were affected by drought as well. Drought also affected many parts of the African continent although dryness was not as pervasive as in 1979. Eastern Europe and the western part of the U.S.S.R. suffered through a remarkably cool and wet spring followed by a remarkably cool and wet summer, and heavy rains falling from India eastward to Indo-China during the summer monsoon resulted in widespread and severe flooding. Many other parts of the world endured adverse weather during 1980, including extreme portions of Africa (drought), the West Indies (Hurricane ``Allen''), Ecuador and Peru (drought), northeastern Brazil (drought), southern Brazil (floods), and northwestern Australia (tropical cyclones). The most ominous and wide-ranging impact of 1980 extreme weather was on world flood supplies.

Le Comte, D. (1982). "International weather in 1981: a year of extremes." Weatherwise, Wash., D.C 35(1): 14-16.

The year began and ended with weather extremes occurring over much of the world, as a highly amplified circulation pattern delivered a potpourri of unusual cold, warmth, and snow during Jan., Feb., and Dec. In the summer, the Soviet Union was baked by a heat wave, and China experienced massive floods. The end of the year saw anomalies of cold, wind, and snow in Europe and Scandinavia. Snow falling on Tunisia on Jan. 8 and 9 was the first seen since 1955. Japan reported that snowstorms took 83 lives and caused one-half billion dollars in property damage. On the North China Plain, water supplies were very low, and dry weather in the spring worsened a drought dating back to the previous July. Moscow temperatures soared to 97 degrees F on July 30. In Europe, an intense storm on July 18-20 resulted in heavy rains and flooding in parts of Austria, West Germany, Czechoslovakia, Hungary, and Poland. July floods killed hundreds and left thousands homeless in northern India, but early withdrawal of the summer monsoon in Aug. led to late-summer drought, causing regional food shortages. Typhoon ``Irma,'' with 140-m.p.h. winds, slammed into the Philippines on Nov. 24, leaving over 273 dead and 250,000 homeless.

Le Comte, D. (1995). "Highlights Around the World." Weatherwise 48(1): 20-22.

Extreme summer heat and dryness prevailed over much of the Northern Hemisphere, including Europe and Japan. Plentiful monsoon rains from Africa to Southeast Asia favored crops, but heavy rains caused flooding and numerous fatalities in southern China and India. Severe drought associated with a resurrected El Nino damaged crops in Australia and Indonesia.

Le Comte, D. (1996). "Highlights around the world." Weatherwise, Washington, DC 49(1): 29-32.

An active monsoon and tropical-cyclone season brought very heavy rains and flooding to many parts of tropical Asia during the summer and autumn, while the end of a long El Nino episode spelled drought relief for Australia. Floods drove thousands from their homes in northwestern Europe early in the year, but drought affected food production in Russia, Spain, Portugal, and Africa. The world's curious 1995 weather is highlighted here.

Leighton, R. M. (1994). "Relationship of anomalies of (anti)cyclonicity to some significant weather events over the Australian region." Australian Meteorological Magazine, Canberra, Australia 43(4): 255-261.

Cyclonicity anomalies for February 1993, December 1993 and January 1994, and anticyclonicity anomalies for April 1993 are presented for the Australian region. The anomalies are based upon 23-year, monthly anticyclonicity and cyclonicity averages. Relationships between the synoptic systems which produced these anomalies, and resultant significant weather events, are discussed. These include: (a) a monsoon low centered in the Kimberly district of western Australia, and resultant record rainfall registered in parts of the Kimberly plateau and central Northern Territory in February 1993; (b) a depression located in eastern Bass Strait, and resultant much above average rainfall recorded across most of Victoria in December 1993; (c) lows in the westerlies centred to the south of Tasmania, together with a heat low positioned across the northern interior of western Australia, and resultant very high temperatures across eastern Queensland and New South Wales, with devasting bushfires over eastern parts of New South Wales in January 1994; and (d) anticyclones located in the western Tasman Sea, and resultant record high average temperature registered across much of eastern Australia in April 1993.

Leroux, M. (1993). "The Mobile Polar High: a new concept explaining present mechanisms of meridional air-mass and energy exchanges and global propagation of palaeoclimatic changes." Global and Planetary Change, Amsterdam, The Netherlands 7(1-3): 69-93.

Air-mass and energy transportation is chiefly made by large lenses of cold air, the Mobile Polar Highs, the key factor of meridional air exchanges, which organize migratory units of circulation in troposphere low levels. Mobile Polar Highs (MPHs) originate in the downwards air motion in high latitudes. The cold air injection organizes a dipolar vortex of very large size (2000/3000 km), the anticyclonic side of this vortex (precisely the MPH) is thin, about 1.5 km thick, by reason of cold air density. Mobile Polar Highs migrate roughly eastwards, with a meridional component towards the tropical zone, through the middle latitudes where they are responsible for weather variability and for rain-making conditions. Their own thermo-dynamic evolution and relief divide them into fragments, and they supply the low-layer of the trade circulation, and eventually the monsoon (previously trade) circulation of a cross-equatorial drift. Eastwards movement and disposition of relief govern the MPHs paths and determine distinct aerological domains; in one of these domains, China is precisely located at the eastern Asian exit of MPHs, stopped by the Himalaya/Tibet range, on their southern side during their eastwards migration. Power of the MPH, connected with its density, as observed in winter in the present conditions, is a function of the initial temperature, namely of the polar radiative conditions. It is precisely in the high latitudes that radiation balance and temperature changes are the most important, at all scales of time, from the seasonal to the palaeoclimatic scale, while in tropical latitudes the changes are comparatively always weak. Two modes of troposphere general circulation are a result of this mechanism: (1) A rapid mode of circulation, connected with a cold situation in polar latitudes, is characterized by strong and extended MPHs and strong winds at all latitudes and all levels. (2) A slow mode of circulation, connected with a warm situation in polar latitudes, is characterized by weak and less extended MPHs, and weak winds at all latitudes and all levels. Insolation and surface boundary conditions of high latitudes are the key control of MPHs dynamics, and therefore the key control of palaeoclimatic changes.

Li, S., L. Ji, et al. (2001). "The maintenance of the blocking over the Ural mountains during the second Meiyu period in the Summer of 1998." Advances in Atmospheric Sciences, Beijing, China 18(1): 87-105.

The 1998 summer-time floods at the Yangtze River basin of China, the severest in last 50 years or so, directly resulted from the abnormal extension of Meiyu (rainy season), which was related to a weak East Asian summer monsoon and persistent anomalies of extratropical circulation. The long persistence of blocking over the Ural Mountains is a conspicuous feature. The physical processes responsible for the prolonged maintenance of this key system are investigated in terms of internal forcing (transient eddy upon basic flow) and external forcing (tropical heating forcing) via diagnosis and numerical experiments in the paper. Using the adjoint method, the location and structure of optimal perturbations favorable for the development and maintenance of Ural blocking are identified, which shows an apparent coincidence with the observed storm track at the eastern Atlantic to Europe sector. The diagnosis of E-vector and the response of baroclinic stationary wave to transient forcing both suggest further that the enhanced transient eddy activity favors the occurrence and maintenance of positive anomalies. The upper-level jet and heat sources (sinks) during that period are calculated, and the results indicate that the anomaly of upper jet and tropical heating is evident. The ensemble forecasting experiments by a GCM, IAP T42L9 show that the anomalous heating over the tropics, especially over the central-western Pacific and Atlantic, favors the formation of positive anomalies of height at the Ural region. Finally, a self-sustain mechanism of positive anomalies through two-way interaction between planetary stationary wave and transient eddy under the stimulation of anomalous tropical heating is proposed.

Li, S., L. Ji, et al. (1999). "Numerical experiments of the west-Pacific subtropical high influenced by heating in South-Asian monsoon area." Journal of Tropical Meteorology, Guangzhou, China 15(2): 106-119.

For a case in which the subtropical high over the western pacific (SHWP) shifted to north-west and mei-yu at Yangtze River valley ended, several numerical experiments on SHWP activity influenced by heating in South-Asia monsoon area are carried out. The results indicate that the enhancement of positive heating in South-Asia will produce one wave train, which propagates north-eastward from the maximum heating center, and one strong positive anomaly center will appear from North-China to Japan in the third day and it will result in the enhancement of SHWP. The comparison of influences upon SHWP between the heating in South-Asia monsoon area and that in ITCZ area south to SHWP is also carried out. It was pointed out that the heating in South-Asia monsoon area is in favor of SHWP movement to the north while the heating in ITCZ area is in favor of SHWP stretch to the west. So far as the response to the influence on SHWP is concerned, the heating over South-Asia monsoon area favors enhancement of SHWP after the third day while the heating over ITCZ south to SHWP but after the fifth day.

Liang, J. Y. and S. S. Wu (2001). "Formation reasons of drought and flood in the rain season of Guangdong and preceding impact factors." Journal of Tropical Meteorology 17(2): 97-108.

With the rainfall data in Guangdong, the grades of drought and flood in both first stage (Apr. similar to June) and second stage (Jul. similar to Sep.) of rain season in Guangdong have been partitioned with Z-index. The grade series in the first stage have 24 years, 6 similar to 8 years and 3 similar to 4 years cycle. The grade series in the second stage have a 10-year cycle, which have been found by Morlet wavelet transform. With compariton between drier and wetter years in the first stage, it has been found that the major reason of rainfall more than normal is the interaction between the stronger southerly in South China Sea and deeper East Asia trough and stronger high jet in East Asia. The major reason for less-than-normal rainfall is that cold air is weaker. The SST in warm pool of western Pacific has an important impact on that interaction. The warmer the SST, the less the rainfall will be in Guangdong. In the paper, we also discuss the forecast technology. It suggests that SST in the warm pool may play as a significant signal for forecasting the drought and flood in the first stage. The atmospheric circulation anomalies in the middle and higher latitude of both Hemispheres shall be taken more notice for forecasting the drought and flood. With compariton between drier and wetter years in the second stage, it has been found that the stronger (weaker) Asia summer monsoon system is a most important factor for the wetter (drier) and the number of landing typhoon is also another influencing factor. It suggests that the height anomalies of preceding May at 500 hPa in (40 similar to 50 degree N, 160 similar to 140 degree W) may play as an significant signal for forecasting the drought and flood in the second stage. The atmospheric circulation anomalies in the middle and higher latitude of Southern Hemisphere can affect the drought and flood through their impact on the Indian summer monsoon.

Lin, P.-H. and L. Ho (1997). "The Asian summer monsoon and Mei-Yu front. Part I: Cloud patterns as a monsoon index." Atmospheric Sciences, Taiwan, Republic of China 25(2): 267-288.

The onset of the Indian summer southwestern monsoon (ISWM), Somali jet and rainfall season arrival on the India Peninsula are the main characteristics of spring-summer seasonal change in Northern Hemispheric circulation. In addition, shallow and transient frontogenesis induced by midlatitude-tropic interaction causes the prolonged rainy period in eastern Asian area. Climate data shows that the onset of eastern Asian summer monsoon (EASM) is barely identified by the general law of monsoon onset phenomenon which relies upon sudden increment of rainfall or sudden change of wind direction. A new and valid monsoon onset index is the basis for this study of EASM dynamics. New cloud patterns were produced by combining radio sounding data and GMS temperature of black-like body data in this study. Four patterns--non-organized convective cloud, organized convective cloud, organized anvil cloud and organized stratus cloud--were used to study EASM circulation evolution from 1985 to 1991. The analysis of cloud pattern time series guided not only the beginning day of Baiu front in Mainland and Japan, (the onset phenomenon of deep convective cloud cells and southwestern flow in Bay of Bengal), but also caught the feature of blend cloud patterns which embedded in the Mei-Yu fronts around Taiwan. The results show that cloud patterns would be a valid monsoon index. Through the convective cloud patterns increment around South China Sea, the transient periods of EASM setup in these seven years were also listed. It suggests that ``transient period'' idea would be more suitable than ``onset'' meanings for EASM circulation setup. Also the main weather feature in the EASM transition period is the quasi-stationary anti-cyclonic circulation on the South China Sea disappearing dramatically. As a ``next step'' we will study the physical mechanism of this phenomenon.

Liu, Y., J. C. L. Chan, et al. (2002). "The Role of Bay of Bengal Convection in the Onset of the 1998 South China Sea Summer Monsoon." Monthly Weather Review 130(11): 2731-2744.

Assimilated analysis fields from the South China Sea Monsoon Experiment and the outgoing longwave radiation data from the National Center for Atmospheric Research (NCAR) have been employed to describe the large-scale and synoptic features of the subtropical circulation during the Bay of Bengal (BOB; 6 '-20 'N, 80 '-100 'E) and South China Sea (SCS; 7 '-20 'N, 110 '-120 'E) monsoon onsets in 1998. The results show that the Asian monsoon onset during May 1998 exhibited a typical eastward development from the BOB region to the SCS domain. The weakening and retreat of the subtropical anticyclone from the SCS were preceded by the intrusion of westerlies and the development of convective activities over the northern part of the SCS (NSCS; 15 '-20 'N, 110 '-120 'E). As the vertical shear of zonal wind changes in sign, the ridge surface of the subtropical anticyclone tilted northward and the summer pattern was established over the SCS. Based on these observational results, version 4 of the NCAR climate model (CCM3) is used to investigate the physical link between the convection associated with the BOB monsoon vortex and the SCS summer monsoon onset, as well as the mechanism of the evolution of the low-level subtropical anticyclone over the SCS. Introduction of heating over the BOB results in vigorous convection over the BOB, and the BOB monsoon onset, as well as the development of westerlies and vertical ascent over the NSCS region due to an asymmetric Rossby wave response. Together with the low-level moisture advection, convection is induced over the NSCS. It is the condensation heating over the NSCS that causes the overturning of the meridional gradient of temperature over the SCS. Consequently the subtropical anticyclone in the lower troposphere over the SCS weakened gradually. Eventually as convection develops over the entire SCS domain, the subtropical anticyclone moves out of the region.

Liu, Y., F. Giorgi, et al. (1994). "Simulation of summer monsoon climate over East Asia with an NCAR Regional Climate Model." Monthly Weather Review, Boston, MA 122(10): 2331-2348.

A summertime season climate over East Asia is simulated with a regional climate model (RegCM) developed at the National Center for Atmospheric Research (NCAR) to validate the model's capability to produce the basic characteristics of monsoon climate over the region. The RegCM used here is a modified version of the NCAR-Pennsylvania State University Mesoscale Model (MM4), in which the Biosphere-Atmosphere Transfer Scheme and a detailed radiative transfer package have been implemented for climate application. The model horizontal resolution is 50 km, and the domain covers a 5200 km x 4700 km area encompassing eastern Asia and adjacent ocean regions. The simulation period is June-August 1990, and the model-driving initial and lateral boundary conditions are from European Centre for Medium-Range Weather Forecasts analyses of observations. The simulated patterns of the monsoon circulation, precipitation, and land-surface temperature are in general agreement with observations, although the model is somewhat too dry and cool. Furthermore, the RegCM captures terrain-induced local rain maxima and temperature centers. Three special aspects of the model results are examined for assessment of model performance: 1) the RegCM reproduces the entire progress of a summer monsoon and the accompanying rain belt, including different steady phases and sudden transitions between two adjacent phases; 2) the paths of tropical storms occurring during the simulated period are closely traced by the model; and 3) realistic patterns of soil moisture are simulated.

Lockwood, J. G. (1985). "World climatic systems." Baltimore, MD., Edward Arnold 292.

This textbook on climatology is designed for students in geography and environmental and related subjects, such as agriculture, at the undergraduate level. There is a minimal use of mathematics requiring no more than a knowledge of algebra and consisting mainly of stated and simply derived or underived equations. The individual chapters consider 1) the general atmospheric circulation: the climatic system; the driving forces; tropical-, middle-, and high-latitude circulation patterns; circulation of energy in the atmosphere; and geological evolution of the general atmospheric circulation; 2) oceanic subsystems: ocean circulation patterns; the atmosphere-ocean interface; tropical and equatorial oceans; tropical temperate weather systems; the polar oceans; and atmosphere-ocean interactions; 3) glacial subsystems: polar climates; physics of large ice sheets; snow and ice on mountains; the history of ice ages through geological time; the Milankovitch theory and the ice ages; 4) arid subsystems: characteristics of desert climate; radiation and temperature, rainfall, evapotranspiration, and water balance in the northern Sahara, North Africa, and Middle East; African rainfall and teleconnections; the Indian monsoon and global deserts; closed lakes and climatic history of North Africa; and desertification; 5) grassland and vegetated subsystems: vegetation and water balance; microclimates of grasslands; evapotranspiration (Bowen ratio); and hydrology of grasslands; 6) forest subsystems: forest microclimates; hydrology and clearance; interception, evaporation, and runoff in tropical forests; 7) climate and energy: climate as an energy source; atmospheric pollution by energy use; climatic controls on energy use; effects of climatic controls on energy use; and effects of climatic variations; and 8) climate and food: climate, plant growth, and grain production; definitions of agricultural drought; teleconnection and drought and increasing atmospheric CO sub(2) . The circulation of energy in the atmosphere, the greenhouse effect, the physics of large ice sheets, vegetation and water balance, atmospheric turbulence, evapotranspiration, and forest microclimates are discussed with the aid of general equations. The derivation of the Bowen ratio and of the Penman and Montieth evapotranspiration equation is presented.

Lockwood, J. G. (1986). "Causes of drought with particular reference to the Sahel." Progress in Physical Geography, London 10(1): 111-119.

Studies published during 1977-1983 on the annual and greater than annual variations in rainfall patterns in several semiarid tropical regions in Brazil and India, and their relationship with the Southern Oscillation and the incidence of drought are reviewed. The association between Indian summer monsoon rainfall and the Southern Oscillation is summarized. Various studies on the causes of drought in the Sahel are surveyed; namely, the role of changes in the atmospheric circulation; the role of changes in sea surface temperature; the biogeophysical feedback mechanism accounting for the persistence of drought in the Sahel proposed by Charney, involving changes in albedo and vegetation cover, and in soil moisture and atmospheric dust content.

Love, G. and G. Garden (1988). "Meteorological overview of the pre-AMEX and AMEX periods over the Australian region." Australian Meteorological Magazine, Canberra 36(2): 91-100.

A synoptic analysis is presented of the tropospheric circulation patterns in the Australian region tropics for the month prior to AMEX phase 2 (Dec. 14, 1986-Jan. 14, 1987) and for the AMEX phase 2 period (Jan. 15-Feb. 15, 1987). These periods are chosen to be representative of two distinctly different tropical flow regimes: the premonsoon onset and the monsoon regime at Darwin. A significant feature shown by the analysis is the rapid evolution from a transition season regime to a monsoon season regime between the two periods. Data are presented showing the time and space scales of the variability of the wind and pressure fields for the six weeks leading up to AMEX and for the AMEX time period, and a synoptic description of the major weather systems affecting the northern Australian region is given. A preliminary analysis is presented describing the role of mesoscale monsoon squall lines in influencing the precipitation regime over northern Australia. Data are presented which show that a high proportion of rainfall received in Darwin during AMEX phase 2 was from such weather systems.

Lu, E. and Y. Ding (1997). "Analysis of summer monsoon activity during the 1991 excessively torrential rain over Changjiang-Huaihe River valley." Quarterly Journal of Applied Meteorology, Beijing, China 8(3): 316-324.

The features of monsoon activity and its role (Jianghuai) during the 1991 excessively torrential rain over Changjiang-Huaihe River valley are analyzed. The results show that the first episodes of torrential rain occurs before the onset of summer monsoon and is mainly induced by synoptic systems in subtropical westerlies; while the activity of southwest monsoon becomes most important during the second and third episodes of torrential rain when subtropical high in West Pacific and southeast monsoon stay stable. The maintenance and break of Meiyu are as a result of the activity of southwest monsoon. A significant effect of southwest monsoon is to transport convective air from tropical area (Arabian Sea and the Bay of Bangal) to Jianghuai valley, thus the convective rain formed in the middle and late stages of the Meiyu is much stronger than that in the normal year, especially in the third episode. The distribution and propagation of strong wind core along southwest airflow are also studied.

Lu, E., Y. Ding, et al. (1998). "Nature of precipitation and activity of cumulus convection during the 1991 Meiyu season of Changjiang-Huaihe River Basin." Acta Meteorologica Sinica, Beijing, China 12(1): 75-91.

Seasonal variability regarding the nature of precipitation and the activity of cumulus convection during the 1991 Meiyu season of Changjiang-Huaihe River Basin (Jianghuai) has been investigated by calculating apparent heat source/apparent moisture sink and analyzing TBB (cloud-top blackbody radiation temperature) data. It is found that three periods of strong ascending motion during the Meiyu season lead to three episodes of heavy rain, and the latent heat due to the precipitation is of the sole heat source of the atmosphere. The nature of precipitation shows distinct seasonal variability, from frontal precipitation of the first episode to the extremely strong convective precipitation of the third episode. TBB field of East Asia may well reflect not only the intensity of convection and rainfall, but also the movement of rain belt and convection belt. In the whole Meiyu season, convection belt mainly stays in Jianghuai, but may shift within the domain of East Asia. Its locating in Jianghuai or not determines the maintenance or break of Meiyu. In the third episode, the narrow convection belt over Jianghuai is mainly caused by southwest monsoon which takes moist and convective atmosphere from tropical ocean.

Luo, H. and M. Yanai (1983). "Large-scale circulation and heat sources over the Tibetan Plateau and surrounding areas during the early summer of 1979, Pt. 1, Precipitation and kinematic analyses." Monthly Weather Review, Boston 111(5): 922-944.

The time evolution of the large-scale precipitation, low-level (850 mb) wind, moisture, and vertical motion fields over the Tibetan Plateau and surrounding areas during a 40-day period from late May to early July 1979 is studied on the basis of the objectively analyzed FGGE Level 2-b data set. During this period, the general circulation over Eastern Asia undergoes a distinct change characterizing the onset of the summer monsoon circulation. The Tibetan Plateau exerts profound orographic and thermal influences upon the low-level wind field. The inflow toward the eastern part of the plateau with a marked diurnal change in its intensity is the most prominent feature of the low-level wind field. The areas of organized precipitation are well related to synoptic systems seen in the 850-mb flow: the quasi-stationary Burma-India trough, the disturbances forming on the trough, the mei-yu (bai-u) front, and the transverse trough extending eastward from the plateau. There is a sharp contrast between the western and eastern plateau in terms of precipitation and moisture distributions. The eastern plateau acts as a huge chimney funneling water vapor from the lower to the upper troposphere. Maxima of 40-day mean upward velocities are located above the eastern plateau, above the Assam-Bengal region, and along the mei-yu frontal zone. The vertical motions above the plateau are more upward in the evening than in the morning. The reverse is true in the surrounding areas. Detailed examinations of daily values of the areal mean vertical p-velocity, mixing ratio, and rainfall are made for four heat source regions (the western plateau and adjacent areas, the eastern plateau, the Yangtse River, the Assam-Bengal region) as a preliminary to the discussion of heating mechanisms operating in these regions.

Luo, Y., Z. Zhao, et al. (2002). "Ability of NCAR RegCM2 in Reproducing the Dominant Physical Processes during the Anomalous Rainfall Episodes in the Summer of 1991 over the Yangtze-Huaihe Valley." Advances in Atmospheric Sciences 19(2): 236-254.

The excessively torrential rainfall over the Yangtze-Huaihe valley during the summer of 1991 is simulated with an updated version of the second generation NCAR regional climate model (RegCM2) as a case study to evaluate the model's performance in reproducing the daily precipitation and the associated physical factors contributing to the generation of the anomalous rainfall. This simulation is driven by large-scale atmospheric lateral boundary conditions derived from the European Center for Medium Range Weather Forecast (ECMWF) analysis. The simulation period is May to August 1991. The model domain covers East Asia and its adjacent oceanic regions. The model resolution is 60 km x 60 km in the horizontal and 23 layers in the vertical. The model can reasonably reproduce the daily precipitation events over East Asia for the summer of 1991, especially in the Yangtze-Huaihe valley where the anomalous rainfall occurred. The spatial and temporal structure of some important physical variables and processes related to the generation of the anomalous rainfall are analyzed. The time evolution of simulated upward vertical motion and horizontal convergence agrees with the five rainfall episodes over this subregion. The water vapor feeding the rainfall is mostly transported by the horizontal atmospheric motions from outside of the region rather than from local sources. The subtropical high over the western Pacific Ocean controls the progress and retreat of the summer monsoon over East Asia, and the RegCM2 can simulate the northward migration and southward retreat of subtropical high over the western Pacific Ocean. Furthermore, the model can represent the daily variation of the low level jet, which is crucial in the water vapor transport to the Yangtze-Huaihe valley.

Lydolph, P. E. (1985). "Weather and climate." Totowa, N.J., Rowman & Allanheld, Publishers 216.

This textbook on weather and climate treats physical synoptic and regional climatology purely descriptively with the aid of numerous graphs, diagrams and maps. It is presumably designed as a short introductory course for students of geography or as a science course for students not planning to engage in a scientific career. This book is an abbreviated form of the longer version, Climate of the Earth, by the same author. The individual chapters cover 1) chemical composition and vertical structure of the atmosphere; 2) global heat exchanges; 3) spatial and temporal variations of the heat budget; 4) atmospheric pressure and atmospheric circulation; 5) observed atmospheric flow, ocean currents, upper atmospheric flow, and divergence and convergence; 6) atmospheric moisture--latent heat water vapor and geographic distribution of evaporation and atmospheric humidity; 7) adiabatic processes and atmospheric stability; 8) air masses and fronts; 9) flow perturbations in middle latitudes--waves, cyclones, thunderstorms, and tornadoes; 10) flow perturbations in lower latitudes--trade wind inversion, easterly waves, hurricanes, equatorial westerlies, and the southeast Asian monsoon; 11) winds; 12) forms and distributions of condensation and precipitation; 13) temperature controls, temperature perception, and expressions and distributions of temperature; and 14) climate classification.

Ma, K.-Y. and L. F. Bosart (1987). "Synoptic overview of a heavy rain event in southern China." Weather and Forecasting, Boston 2(2): 89-112.

The meteorological events surrounding the heavy rains of June 23-25, 1983, in the Yangtze River Valley of China are investigated. The rains developed along a persistent quasi-stationary frontal boundary that separated warm, moist, tropical air from slightly cooler continental air. The frontal zone was characterized by a thermally direct circulation driven by horizontal confluence in the lower troposphere. Aloft, the flow was broadly anticyclonic. A mobile 500-mb short-wave trough moved eastward in the westerlies north of the Quinghai-Xizang Plateau. In its wake, cooler and drier Siberian air was funneled southward, east of the plateau, to reinforce the baroclinic zone. A very weak short-wave trough also moved eastward in the much weaker 500-mb monsoon westerlies south of the plateau. The arrival of the cooler air from the north and the weak trough from the southwest invigorated a preexisting cyclonic circulation over the Sichuan Basin. A massive mesoscale convective system erupted in a complex interaction of these features with the local topography. The generation of a midlevel cyclonic vorticity maximum by the mesoscale convective complex appeared to be comparable to what has been seen in similar cases over North America. Warm air advection in the lower troposphere appeared to help trigger the rainfall through weak synoptic-scale ascent of 1-2 cm sec super(-) super(1) . An analysis of the water vapor flux revealed the South China Sea as a moisture source in the surface-to-850-mb layer and the Indian subcontinent-Bay of Bengal region as the moisture source in the 850-500-mb layer.

Mahanti, A. C. (1981). "Stability of monsoon depression." Archives for Meteorology, Geophysics and Bioclimatology, Ser A, Vienna 30(1/2): 39-53.

The object of this paper is to study the stability of a monsoon depression which is a low-level wave disturbance over the Indian region during summer. The stability of a wave disturbance depends intimately upon the phase velocity. The phase velocity of the Rossby gravity wave does not explain the phase velocity of a monsoon depression. Thus, since the convective activity plays an important role in the development of a monsoon depression, the phase velocity of zonally propagating Rossby gravity waves is modified, i.e., the modified dispersion relation considering the effect of convective heating in the equivalent barotropic model, which is derived for the low levels in the Tropics, is obtained. The modified dispersion relation explains the phase velocity of monsoon depression. Beyond the limiting stage, there is no additional depression of the central pressure. Thus, it is essential to study the stability of a monsoon depression at the limiting stage. The stability analysis shows that the monsoon depression is neutral (i.e., it does not break down) as long as there is convective activity, but the monsoon depression becomes unstable (i.e., breaks down) if the convective activity ceases. In the latter case, a possible stream of zonal wind is obtained.

Manikiam, B. and S. Sridharan (1988). "Statistical study of synoptic systems causing significant rainfall over Tamil Nadu during southwest monsoon season." Mausam, New Delhi 39(3): 287-290.

A statistical analysis of the 5-yr data (1975-1979) has been conducted to study the occurrence of various synoptic systems that cause significant rainfall (scattered-fairly widespread-widespread) over Tamil Nadu during the southwest monsoon season. It is seen that the occurrence of the synoptic systems--surface trough (with or without upper air cyclonic circulation) and low pressure area--is dependent upon the position of the monsoon trough with regard to the normal. There is a high probability of occurrence of surface trough with cyclonic circulation and low-pressure area when the monsoon trough is to the north of its normal position. The probability of occurrence of significant rainfall is higher in low-pressure areas (66%) compared to sea level troughs with or without cyclonic circulation (20%).

Manikiam, B. and S. Sridharan (1989). "Cloud patterns in the NE monsoon season." Mausam, New Delhi 40(1): 61-64.

The rainfall over Tamil Nadu during the NE monsoon occur mostly in association with low pressure areas and depressions. With the advent of satellites, it has been possible to study the weather systems in greater detail. In this study, the daily NOAA-data for the NE monsoon season (October and November) for the period 1979-1985 has been utilised to classify the synoptic systems into several cloud patterns. It has been found that the most frequently occurring cloud patterns are the amorphous and the banding type. The occurrence of the cloud patterns vis-a-vis synoptic situations has been analysed and meaningful results obtained.

Mapes, B. and R. A. Houze, Jr. (1992). "An integrated view of the 1987 Australian monsoon and its mesoscale convective systems. I: Horizontal structure." Quarterly Journal of the Royal Meteorological Society, Berkshire, England 118(507): 927-963.

This observational study is organized around three issues: the forcing of the monsoon flow by embedded deep convection, the thermodynamic conditions that support the convection, and the structures of the mesoscale convective systems (MCSs) that constitute much of the deep convection. The monsoon convective cloudiness occurred predominantly offshore, over the earth's warmest waters. Week-long periods of widespread deep convection caused cycles of monsoon spin-up, culminating in tropical-cyclone formation. Momentum transports by the convection also created smaller-scale vortex pairs in the upper troposphere. Sounding data suggest that the convection was modulated by low-level processes, not by large-scale deep forced ascent. Triggering by mesoscale boundary-layer cold-pool boundaries and coastlines determined specifically where convection occurred, while several positive feedbacks acted to keep regional thermodynamic conditions favourable. Hence monsoon convection, once initiated, persisted as self-exciting `superclusters', composed at any instant of many distinct MCSs. The observed MCSs all contained areas of deep convection and stratiform precipitation areas. Stratiform precipitation usually evolved in place from convective cells, although precipitation also occasionally fell from overhanging anvils created by upper-level shear. The MCSs within similar synoptic wind environments tended to have similar mesoscale structures. This fact reflects the effects, illustrated herein, of environmental winds upon the relative motions of cold pools (which trigger new convective cells) and stratiform precipitation areas (which evolve from old convective cells).

McBride, J. L., N. E. Davidson, et al. (1995). "The flow during TOGA COARE as diagnosed by the BMRC tropical analysis and prediction system." Monthly Weather Review, Boston, MA 123(3): 717-736.

The evolution of the large-scale flow through the four-month intensive period of TOGA COARE is documented from large-scale numerical analyses and GMS cloud imagery produced by the Australian Bureau of Meteorology and transmitted to the field stations during the experiment. The evolution of the flow is dominated by the following phenomena: 1) the normal seasonal evolution of the tropical flow over this region, including a southward and eastward progression of the tropical convective heat source as the Southern Hemisphere monsoon developed and matured; 2) a more eastward than normal progression of this monsoon circulation, associated with a warm event of the ENSO phenomenon; 3) the existence of a major westerly-easterly-westerly cycle of the Madden-Julian low-frequency wave occurring during the latter half of the experimental period; and 4) the development and subsequent movement of tropical cyclones in both (Northern and Southern) hemispheres. The Madden-Julian event consisted of two eastward progressions across the domain of satellite-observed cloud, south of the equator. The horizontal scale of the cloud regions is approximately 10 degrees latitude x 40 degrees longitude and the eastward phase speed is approximately 3.7 m s super(-) super(1) . Linear correlation studies substantiate the eastward movement of both cloud and zonal wind across the domain. The correlation analysis reveals a strong relationship between cloud and low-level zonal wind, with the cloud variations leading those in wind by approximately five days. Time-longitude sections of relative vorticity show that the synoptic activity also progressed eastward with the cloud, and its structure is suggestive that the controlling dynamics (for the synoptic activity) may be the energy dispersion mechanism of Davidson and Hendon. The development of each westerly event was accompanied by a major change in the Southern Hemisphere deep-layer mean flow from easterly to westerly. Examination of flow fields and satellite imagery for individual days shows that the peak of the first westerly event is associated with the flow patterns surrounding two Southern Hemisphere tropical cyclones. The subsequent rapid evolution to an easterly state occurs as the cyclones move eastward and southward, and the monsoon flow collapses in their wake. There is an accompanying ridging at low levels in the subtropics and the establishment of the Southern Hemisphere subtropical jet. The subsequent reestablishment of the monsoon (the second westerly event) occurs from west to east with the eastward moving cloud bands. There is also a suggestion that an equatorward extension of a Southern Hemisphere upper-level trough may have played a role. Major active and break periods are identified over four tropical subdomains over the TOGA COARE region. These are most easily defined in the Southern Hemisphere subdomains. They are characterized by a slowly varying signal in the satellite-observed average cloud-top temperature. Superimposed on this is a rapid transition between the active and break states.

McBride, J. L. and E. E. Ebert (2000). "Verification of quantitative precipitation forecasts from operational numerical weather prediction models over Australia." Weather and Forecasting, Boston, MA 15(1): 103-121.

Real-time gridded 24-h quantitative precipitation forecasts from seven operational NWP models are verified over the Australian continent. All forecasts have been mapped to a 1 degrees latitude-longtitude grid and have been verified against an operational daily rainfall analysis, mapped to the same grid. The verification focuses on two large subregions: the northern tropical monsoon regime and the southeastern subtropical regime. Statistics are presented of the bias score, probability of detection, and false alarm ratio for a range of rainfall threshold values. The basic measure of skill used in this study, however, is the Hanssen and Kuipers (HK) score and its two components: accuracy for events and accuracy for nonevents. For both regimes the operational models tend to overestimate rainfall in summer and to underestimate it in winter. In the southeastern region the models have HK scores ranging from 0.5 to 0.7, and easily outperform a forecast of persistence. Thus for the current operational NWP models, the 24-h rain forecasts can be considered quite skillfull in the subtropics. On the other hand, model skill is quite low in the northern regime with HK values of only 0.2-0.6. During the summer wet season the low skill is associated with an inability to simulate the behavior of tropical convective rain systems. During the winter dry season, it is associated with a low probability of detection for the occasional rainfall event. Thus it could be said that models have no real skill at rainfall forecasts in this monsoonal wet season regime. Model skill falls dramatically for occurrence thresholds greater than 10 mm day super(-) super(1) . This implies that the models are much better at predicting the occurrence of rain than they are at predicting the magnitude and location of the peak values.

McBride, J. L. and G. J. Holland (1989). "Australian Monsoon Experiment (AMEX): early results." Australian Meteorological Magazine, Canberra 37(1): 23-35.

The objectives of the Australian Monsoon Experiment (AMEX) were: 1) to investigate the interactions between cumulonimbus convection and the Australian summer monsoon circulation; and 2) to investigate the generation, evolution, and propagation mechanisms of north Australian cloud lines, and to study their effect on north Australian weather. The experiment was based upon the collection of high-density tropical upper air soundings and radar and satellite data during two observational phases in Oct.-Nov. 1986 and Jan.-Feb. 1987. The second phase was complementary to, and conducted as a collaborative exercise with, the research aircraft-based EMEX and STEP experiments. The field phases of AMEX were extremely successful. Atmospheric phenomena captured within the observational network include more than 10 north Australian cloud lines, the monsoon onset, and two active-inactive cycles of monsoon convection. Additionally, during Phase II, four tropical cyclones developed within the network, including two within an similar to 500-km-diameter circle of radiosondes surrounding the Gulf of Carpentaria. This paper describes some of the highlights obtained from analysis of the data in the first year following the completion of the field phases, with emphasis on aspects of the meteorology that were not known prior to the experiment.

McBride, J. L. and T. D. Keenan (1982). "Climatology of tropical cyclone genesis in the Australian region." Journal of Climatology, Chichester, Eng 2(1): 13-33.

Statistics of tropical cyclone origin in the Australian region are presented for the period July 1959-June 1979. Cyclone genesis is found to occur in preferred areas and to have a high incidence of coastline developments, often with the precursor system forming over land. There is an average of 1.3 occurrences per year of regeneration whereby a cyclone develops from a pre-existing cyclone that has lost intensity after crossing onto the continent. A synoptic analysis of individual developments over 5-yr reveals that 84% of the precyclone cloud clusters first appear on the gradient-level monsoon shear line, whereas 97% are on the shear line at the point of development. Statistical evidence is given for the enhancement of lower and upper level vorticity fields by midlatitude systems prior to cyclone genesis, but on a case-by-case basis, the role of these systems is highly variable. The structure of the precyclone systems for individual cases and composites shows the upper level warm core and large-scale cyclonic surrounding circulation in the middle and lower troposphere, known to exist for similar systems in other parts of the world. At upper levels, the systems are surrounded by tangential winds in the anticyclonic sense beyond 6 degrees lat. radius.

Membery, D. (2002). "Monsoon tropical cyclones: Part 2." Weather 57(7): 246-255.

Part 1 of this article (Membery 2001) introduced the idea of `monsoon tropical cyclones' in the Arabian Sea - cyclones that form preferentially during the four-week period from mid-May to mid-June as a response to changes imposed on the region by the developing Asian monsoon. Part 2 highlights five well-developed cyclones that formed off the west coast of India during the same four-week period and subsequently tracked either westwards or northwestwards towards Arabia.

Mills, G. A. and S. Zhao (1991). "A study of a monsoon depression bringing record rainfall over Australia. Part I: Numerical predictability experiments." Monthly Weather Review, Boston, MA 119(9): 2053-2073.

Between 11 and 15 March 1989, a low pressure system developed in the monsoon trough over the northwest coast of Western Australia. Subsequently an intense precipitating depression moved southeastwards across Australia, bringing flood rainfall to a wide area of the driest parts of the continent. The synoptic-dynamic aspects of this case are described in a companion paper. A series of studies are presented in this paper, examining various aspects of the numerical predictability of this event. Forecasts are compared from a static cold start analysis (the operational system at the time), a limited-area data assimilation system with operational (2.5 h) data cutoffs, and the same assimilation system with an infinite data cutoff. It is shown that the operational forecasts of the cyclone's position, intensity, and precipitation were clearly inferior to both assimilation forecasts. The assimilation forecasts of rainfall subjectively showed a greater margin of improved skill over the operational forecasts based at 1200 UTC than they did for the 0000 UTC-based forecasts. This suggests that the assimilation system, by the use of model feedback in the first-guess fields and the greater use of remotely sensed data, is less sensitive to the variations in radiosonde data density at 1200 UTC than was the operational system. The late data cutoff assimilation forecasts were superior to those with the operational cutoffs, and it was shown by a sensitivity experiment that most of this improvement was due to the inclusion of satellite sounding data from the TIROS series of orbiting satellites (TOVS data), which do not arrive in time for the operational 0000 and 1200 UTC analyses. This suggests that when locally processed TOVS data become available, an improvement in forecast skill should be realized. A series of model sensitivity experiments, in which forecasts are compared with and without the precipitation parameterization activated show that the forecast intensification of the low as it crossed the continent was significantly aided by feedback from latent heat release. Another interesting point resulting from these sensitivity experiments is that latent heat feedback contributed to the forecast intensification of the jet stream well downstream of the precipitating depression.

Min, W. and S. Schubert (1997). "The climate signal in regional moisture fluxes: a comparison of three global data assimilation products." Journal of Climate, Boston, MA 10(10): 2623-2642.

This study assesses the quality of estimates of climate variability in moisture flux and convergence from three assimilated datasets: two are reanalysis products generated at the Goddard Data Assimilation Office and the National Centers for Environmental Prediction-National Center for Atmospheric Research, and the third consists of the operational analyses generated at the European Centre for Medium-Range Weather Forecasts (ECMWF). The regions under study (the United States Great Plains, the Indian monsoon region, and Argentina east of the Andes) are characterized by frequent low-level jets and other interannual low-level wind variations tied to the large-scale flow. While the emphasis is on the reanalysis products, the comparison with the operational product is provided to help assess the improvements gained from a fixed analysis system. All three analyses capture the main moisture flux anomalies associated with selected extreme climate (drought and flood) events during the period 1985-93. The correspondence is strongest over the Great Plains and weakest over the Indian monsoon region reflecting differences in the observational coverage. For the reanalysis products, the uncertainties in the lower tropospheric winds is by far the dominant source of the discrepancies in the moisture flux anomalies in the middle latitude regions. Only in the Indian Monsoon region, where interannual variability in the low-level winds is comparatively small, does the moisture bias play a substantial role. In contrast, the comparisons with the operational product show differences in moisture that are comparable to the differences in the wind in all three regions. Compared with the fluxes, the anomalous moisture convergences show substantially larger differences among the three products. The best agreement occurs over the Great Plains region where all three products show vertically integrated moisture convergence during the floods and divergence during the drought with differences in magnitude of about 25%. The reanalysis products, in particular, show good agreement in depicting the different roles of the mean flow and transients during the flood and drought periods. Differences between the three products in the other two regions exceed 100% reflecting differences in the low-level jets and the large-scale circulation patterns. The operational product tends to have locally larger amplitude convergence fields, which average out in area-mean budgets: this appears to be at least in part due to errors in the surface pressure fields and aliasing from the higher resolution of the original ECMWF fields. On average, the reanalysis products show higher coherence with each other than with the operational product in the estimates of interannual variability. This result is less clear in the Indian monsoon region where differences in the input observations appear to be an important factor. The agreement in the anomalous convergence patterns is, however, still rather poor even over relatively data-dense regions such as the United States Great Plains. These differences are attributed to deficiencies in the assimilating general circulation model's representations of the planetary boundary layer and orography, and a global observing system incapable of resolving the highly confined low-level winds associated with the climate anomalies.

Mishra, D. K. and M. S. Singh (1977). "Study of the monsoon depression intensifying into cyclonic storm over land." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 28(3): 321-327.

The monsoon depression that formed over the head of the Bay of Bengal and nearby areas on Sept. 8, 1970, and crossed the West Bengal coast near Contai on the evening of the 9th, had some unusual features. It progressively intensified into a cyclonic storm over the land, although its development was slow. It executed a loop around Kanpur. This system caused heavy rainfall along its track, particularly over the southern parts of Uttar Pradesh. A study of this depression, by means of weather satellite cloud pictures, is presented in this paper.

Mitra, A. K., A. K. Bohra, et al. (1997). "Daily rainfall analysis for Indian summer monsoon region." International Journal of Climatology, Chichester, UK 17(10): 1083-1092.

A simple method of daily rainfall analysis on a regular latitude by longitude grid over the Indian monsoon region is described. Daily rainfall estimates obtained from INSAT IR radiances and rain-gauge observations are combined to produce this analysis. A case of a typical westward moving monsoon depression during the 1994 monsoon season is chosen to present the characteristics of the rainfall analysed. The results obtained show that the analysis is able to represent adequately the large-scale distribution of the rainfall realized, which can further be used for modelling studies. By inserting rain-gauge observations it is seen that, in general, the final analysis removes the large negative bias imposed by the satellite estimates. Owing to the non-availability of the precipitable water estimates over this region in real time, at present, there is a necessity to have alternative procedures for analysed rainfall distribution, especially for the purposes of physical initialization and other related applications of the tropical numerical weather prediction. When the Special Sensor Microwave Instrument (SSM/I) and other estimates from the Tropical Rainfall Measuring Mission, etc. become available in future the present scheme will be able to include these new products also for improving the quality and representation of rainfall over oceanic region.

Miyazaki, Y. (1989). "The relationship between tropical convection and winter weather over Japan." Journal of the Meteorological Society of Japan, Tokyo, Japan 67(5): 863-875.

The relationship among tropical convection, the weather over Japan, and the atmospheric circulation in the Northern Hemisphere during winter was statistically examined with the use of monthly mean temperature data over Japan, outgoing longwave radiation (OLR), 500 mb geopotential heights and the sea level pressure. It was found that the temperature over Japan is highly correlated with convective activity around the Philippines, i.e., when the convection around the Philippines is active, the temperature over Japan is lower than normal. Conversely, when the convection is inactive, temperatures over Japan are above normal. Convective activity around the Philippines is also correlated with the Northern Hemisphere 500 mb geopotential heights, especially in the region of east Asia. When convective activity around the Philippines is strong, the 500 mb heights around Japan are lower while those around Siberia are higher. Weak convection means higher 500 mb heights over Japan and low heights over Siberia. Sea level pressure in the northwest Pacific east of Japan is lower while that in Siberia is higher for active convection cases. The converse is true for inactive convection. Conclusions from these results indicate that for active convection the strength of the east Asia winter monsoon becomes stronger resulting in a cold winter over Japan. Inactive convection weakens the east Asian winter monsoon creating a warm Japanese winter. The results of composite analyses show that the global height anomaly patterns such as the Eurasian and Pacific/North American patterns can be found more clearly in the active convection cases than in the inactive cases.

Miyazaki, Y. (1989). "Relationship between tropical convection and winter weather over Japan." Journal of the Meteorological Society of Japan, Tokyo 67(5): 863-875.

The relationship among tropical convection, the weather over Japan and the atmospheric circulation in the Northern Hemisphere during winter was statistically examined with the use of monthly mean temperature data over Japan, outgoing longwave radiation (OLR), 500-mb geopotential heights and the sea level pressure. It was found that the temperature over Japan is highly correlated with convective activity around the Philippines, i.e., when the convection around the Philippines is active, the temperature over Japan is lower than normal. Conversely, when the convection is inactive, temperatures over Japan are above normal. Convective activity around the Philippines is also correlated with the Northern Hemisphere 500-mb geopotential heights, especially in the region of east Asia. When convective activity around the Philippines is strong, the 500-mb heights around Japan are lower while those around Siberia are higher. Weak convection means higher 500-mb heights over Japan and low heights over Siberia. Sea level pressure in the northwest Pacific east of Japan is lower while that in Siberia is higher for active convection cases. The converse is true for inactive conviction. Conclusions from these results indicate that for active convection the strength of the east Asia winter monsoon becomes stronger resulting in a cold winter over Japan. Inactive convection weakens the east Asian winter monsoon creating a warm Japanese winter. The results of composite analyses show that the global height anomaly patterns such as the Eurasian and Pacific/North American patterns can be found more clearly in the active convection cases than in the inactive cases.

Mo, K., G. D. Bell, et al. (2001). "Impact of Sea Surface Temperature Anomalies on the Atlantic Tropical Storm Activity and West African Rainfall." Journal of the Atmospheric Sciences [J. Atmos. Sci.]. 58(22).

The association between rainfall over the Sahel and Sudan region and tropical storm activity in the Atlantic is examined using the NCEP-NCAR reanalysis and sea surface temperature anomalies (SSTAs) from 1949 to 1998. Evidence indicates that both are influenced by global SSTAs. The SSTA modes generating favorable atmospheric conditions for tropical storms to develop are also in favor of a wet rainfall season in the Sahel and Sudan region. The easterly waves over West Africa become tropical storms only if the atmospheric conditions over the Atlantic are favorable. These conditions are responses to SSTAs. In addition to ENSO, a multidecadal trend mode also plays a role. The positive phase of the trend mode features positive loadings in the North Pacific and the North Atlantic, and negative loadings over the three southern oceans. The positive (negative) phases of both modes are associated with increased (reduced) Atlantic tropical storm activity, and with wet (dry) West African monsoon seasons. The SSTAs over the tropical South Atlantic (S-ATL) are related to the rainfall dipole over West Africa, but the influence on tropical storms is not large. Warm (cold) SSTAs over the tropical North Atlantic enhance (suppress) the occurrence of tropical storms, but have little influence on rainfall over West Africa. The most prominent circulation features associated with the positive phases of SSTA modes are enhanced upper-level 200-hPa easterly winds and reduced vertical wind shear in the main development region of the tropical Atlantic, which are well-known features of active Atlantic tropical storm seasons. The associated low-level flow shows enhanced anomalous westerly winds across the Atlantic to Africa. That allows more moisture transport into Africa and, therefore, more rainfall.

Modi, V. and S. P. Sukhatme (1979). "Estimation of daily total and diffuse insolation in India from weather data." Solar Energy, Oxford 22(5): 407-411.

Insolation and weather data for a large number of cities in India are analyzed and correlated. Correlations based on a citywise regression analysis indicate that daily total insolation correlates best with sunshine duration, all clouds, and precipitation. These relations are not useful for predicting insolation at locations where this data is not measured. Monthwise correlations that are valid over a region are more useful; hence, such correlations were developed for Indian conditions. To increase the accuracy of prediction of these correlations, India is divided into two regions on the basis of the climatic characteristics of the winter monsoon. The Liu and Jordan model for predicting daily diffuse radiation from daily total radiation was tested and found to be applicable to Indian conditions; however, the numerical values obtained are different from those obtained for conditions in the U.S.

Mohanty, U. C. (1989). "Evaluation of a multi-level primitive equations limited area model for short range prediction over Indian region." Mausam, New Delhi 40(1): 29-36.

A five-level primitive equations limited area model (LAM) in flux form is considered in this study for short range prediction in the Tropics. The model physics includes boundary layer, dry convective adjustment, deep cumulus convection and large scale condensation. The effect of mountains including Himalayas is incorporated through sigma coordinate formulation. An efficient split-explicit time integration scheme with time dependent lateral boundary conditions are used. This study addresses the problem of short range numerical weather prediction over the Indian sub-continent during SW monsoon season. The model is integrated up to 48 hours with four typical cases representing a cut-off low, onset vortex, mid-tropospheric cyclone and monsoon depression situation during special observing period-II (MONEX) of the FGGE-1979. The model produced reasonably good forecasts of surface pressure, wind and temperature fields up to 48 hours. However, the precipitation forecasts were not very satisfactory.

Mohanty, U. C. and N. Mohan Kumar (1991). "A method of estimating long-wave radiation over the Indian seas based on surface synoptic observations." Mausam, New Delhi, India 42(4): 375-380.

An attempt has been made to estimate long-wave radiative flux from sea surface using semi-empirical models with the help of routinely observed meteorological parameters during the monsoon season. The estimated values are then compared with observed values to find out an appropriate method to compute the long-wave flux. The study shows that clouds play an important role in determining the long-wave flux. It is found that lack of detailed knowledge of clouds obtained from ground based observations is responsible for the errors in the estimation of long-wave flux. The errors are reduced using a regression method based on Monsoon-77 data set. The method was then tested with Monex-79 data set which served as independent data set. The method thus developed considerably reduces the errors associated with the estimation of long-wave flux.

Mooley, D. A. and J. Shukla (1989). "Main features of the westward-moving low-pressure systems which form over the Indian region during the summer monsoon season and their relation to the monsoon rainfall." Mausam, New Delhi 40(2): 137-152.

The main features of the transitory monsoon low-pressure systems (LPS) over the Indian region during the period 1888-1983, in regard to their formation, life, movement, intensity, and dissipation, as well as their interannual variability are examined by utilizing the information and data contained in the Indian Daily Weather Reports. The relationships of these features to the monsoon rainfall over India, north India, central India, and south India are examined. The paper discusses a variety of statistics about low-pressure systems, e.g., their formation, location, life, intensity, movement, and dissipation. The number of LPS formed is not significantly related to the monsoon rainfall over India except for a weak relationship with central India monsoon rainfall. The number of LPS days during the season is significantly and directly related to the Indian monsoon rainfall (above 5%) and to central India monsoon rainfall (above 1%), and these relationships generally show good stability. Total westward longitudinal displacement of the LPS during the season and the monsoon rainfall over India and central India are directly and significantly (above 1%) related, and these relationships also generally show good stability.

Moray, P. E. (1976). "Southwest monsoon over Gujarat region: typical situations of droughts and exceptionally heavy rain." Symposium on Tropical Monsoons, Poona, India, Sept.

In this paper, synoptic situations over Gujarat region (including Saurashtra and Kutch) are studied. After reviewing the general meteorological conditions over the area, a survey is made of the synoptic systems affecting the Gujarat region. Rainfall data for the last 30 yr from the selected stations in the region are also analyzed in relation to the southwest monsoon, a main source of rainfall over the region. Typical synoptic situations giving exceptionally heavy rain over some areas and synoptic conditions of break monsoon leading to drought occurrences are also discussed.

Mukabana, J. R. and R. A. Pielke (1996). "Investigating the influence of synoptic-scale monsoonal winds and mesoscale circulations in diurnal weather patterns over Kenya using a mesoscale numerical model." Monthly Weather Review, Boston, MA 124(2): 224-243.

The Regional Atmospheric Modeling System (RAMS) developed at Colorado State University (CSU) was used to investigate the influence of the large-scale monsoonal winds and the mesoscale local circulations on the diurnal precipitation pattern over Kenya. Three basic experiments were performed. In the first control experiment (CONTROL), RAMS was initialized using observational data (``variable initialization'') from the global analyzed ECMWF 2.5 degrees x 2.5 degrees data of 0000 UTC 14 April 1985. The model was integrated forward in time for 24 h to simulate the large-scale flow fields over Kenya. Full physics including moist convection were implemented in the model. The model outputs were validated against available observations in order to determine the ability of the model in replicating the synoptic climatology prevailing over the study domain. In the second experiment (MESO), the model simulation was started from an atmosphere at rest in order to exclude the large-scale flow from the model runs. This experiment used a horizontally homogeneous procedure to initialize the model. Moist convection was allowed to occur in the mesoscale simulations. The third experiment (SYNO) excluded topography and land-water contrast data from the simulation. This was done in order to suppress the thermally induced local mesoscale circulations from the model runs so as to isolate and determine the role played by the synoptic-scale monsoonal winds on the generation of precipitation over Kenya. Topography was considered a local forcing that significantly modifies the large-scale temperature, moisture, and flow pattern. Comparison was made between grid-averaged convective precipitation generated in the CONTROL, MESO, and SYNO simulations in order to identify the contribution of the synoptic-scale monsoonal flow and mesoscale circulations on the rainfall over Kenya. Additional sensitivity experiments were performed to test the impact of topography and large water bodies on the precipitation over the country. The results showed the following. More active convection developed in regions where the large-scale monsoonal winds in the lower troposphere converged with the local mesoscale circulations embedded in the large-scale flow. : The large-scale flow advected substantially more moisture into the study domain as compared to the mesoscale flow alone. This illustrated the fact that monsoonal winds transport moisture from the Indian Ocean and advect it inland over the country. : The large-scale monsoonal flow controlled the locations and movement of the convergence/precipitating zones over the country since the deep and active convective zones shifted in the direction of the prevailing low-level large-scale monsoonal flow. : Topography has a significant impact on the diurnal precipitation pattern over the country. It generates anabatic-katabatic winds, with a strong diurnal cycle; it modifies the large-scale temperature, moisture, and wind flow patterns over the country; and it also inhibits a substantial amount of the moisture-laden monsoonal winds from reaching farther inland over the country. : The large water bodies (Lake Victoria, Lake Turkana, and the Indian Ocean) generate strong lake-land, sea-land-breeze circulations with an intense diurnal cycle that contributes to the overall precipitation pattern over the country. It was concluded that the large-scale monsoonal winds and the mesoscale circulations are both crucial components in the realization of rainfall in Kenya during a wet season. The study similarly revealed the ability of the high-resolution RAMS model to replicate realistic meteorological fields far both large-scale and mesoscale weather systems in an equatorial regime.

Mukherjee, A. K., G. Gurunadham, et al. (1978). "Clouding over the Arabian Sea and the synoptic situation over India during monsoon." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 29(1/2): 118-124.

Satellite cloud pictures for the period 1971-1975 were analyzed to examine the coverage and type of clouding over the Arabian Sea in relation to two main synoptic features of the monsoon season, i.e., 1) break in monsoon and 2) movement of monsoon depressions. It is found that whenever breaks appear and the monsoon trough goes to the foot of the Himalayas, the Arabian Sea north of 15 degrees N lat. is covered with stratocumulus cloud lines. With the revival of the monsoon, these cloud lines decrease. This situation continues when the monsoon depressions form and move westward until they come to 80 degrees E long. When the monsoon depressions move further, either to the west of 80 degrees E long. or to the north of 25 degrees N lat., the stratocumulus cloud lines increase over the Arabian Sea.

Mukherjee, A. K. and K. P. Padmanabham (1977). "Simultaneous occurrence of tropical cyclones on either side of the Equator in the Indian Ocean area." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 28(2): 211-222.

Malurkar (1950) postulated the formation of depressions or cyclones on both sides of the Equator within a narrow ( greater than or equal to 40 degrees ) longitudinal belt. Pisharoty and Kulkarni (1956) conducted case studies and came to the conclusion that they do form as postulated by Malurkar, and that there is mutual interaction with one another so much that when one system intensifies the other weakens. Kuettner (1967) opined that the existence and alignment of hills in Sumatra are responsible for simultaneous occurrences of storms and depressions on both sides of the Equator. To verify these conclusions, the present study was undertaken. It covers an 11-yr period from 1964 to 1974. During this period, as many as 14 storms /depressions formed on both sides of the Equator. There were some years in which such systems did not develop. They form in transition months with a bias toward the post monsoon season. Kuettner's conclusions are generally supported. Pisharoty and Kulkarni's conclusions could not be supported by this study. Malurkar's conclusion, that two tropical storms cannot both continue to move westward and coexist on either side of the Equator when the longitudinal separation is small ( greater than or equal to 10 degrees ), is also supported.

Mukherjee, A. K., M. K. Rao, et al. (1978). "Vortices embedded in the trough of low pressure off Maharashtra-Goa coasts during the month of July." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 29(1/2): 61-65.

Two troughs of low pressure are generally noticed over the Indian region during the monsoon season. One is the monsoon trough over the Gangetic Plain, which persists throughout the monsoon season. The other is a comparatively less pronounced trough persisting off the west coast of India, which is most prominent during July. Vortices embedded in these troughs cause a considerable amount of rainfall. While the vortexes and low-pressure areas associated with the monsoon trough passing over the Gangetic Plain have been studied extensively, those embedded in the trough off the west coast have not received enough attention. In this paper, the latter vortexes during July are studied. The following conclusions are made. These vortexes are most prominent during July. They have a tendency to form in series during the first half of July, just south of Goa. They generally move northward with an approximate speed of 100 km per day. During the second half of the month, some of them move north-westward, and heavy rainfall associated with them brings more rain to the coastal stations than to the Ghats. There may be an association between the formation of the series of vortexes, during the first half of July and the existence of an upper air cyclonic circulation between 2.1 and 3.6 km a.s.l. over the Gujarat region and its neighborhood.

Mukherjee, A. K. and B. Shyamala (1978). "Distant effects of monsoon depressions on weather over west Rajasthan." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 29(1/2): 47-53.

Monsoon depressions are generally responsible for increased rainfall activity over northern and central parts of India during the southwest monsoon season. They also have some influence on the weather over places some distance from the depression. One such effect mentioned by K. L. Sinha is that whenever monsoon depressions/lows form in the Bay of Bengal or interior and move in a west-northwesterly direction, rain or thundershowers occur over Jodhpur. This phenomenon of distant effects of monsoon depression on weather over west Rajasthan has been studied for the 20-yr period from 1956 to 1975. On 70% of the occasions when monsoon depressions/lows formed in the northwest Bay and crossed the Orissa coast, distribution and activity of rainfall over west Rajasthan showed a prominent increase. An explanation for this phenomenon is offered in this study in terms of a southward shift of the mid-tropospheric trough line. Occasions when the depressions/lows were over or near west Rajasthan have been excluded from this study.

Mukherjee, A. K. and B. Shyamala (1985). "Rainfall activity along the west coast of India at the formative stage of monsoon depression." National Seminar cum Workshop on Atmospheric Science and Engineering, Calcutta, India, Feb.

At the time of the formation of monsoon depressions over northwest /head Bay (sic), forecasters generally issue heavy rainfall warnings for the Maharashtra-Karnataka coasts; but heavy rainfall is not realized in all cases. The circulation aspects and rainfall activity over the west coast of India at the time of the formation of the depressions have been investigated so as to identify the synoptic differences between the occasions when the rainfall activity along the west coast increases with a depression forming over northwest/head Bay (sic) and when it does not. It is found that the development of a cyclonic circulation over the northeast Arabian Sea and adjoining areas in the lower tropospheric levels, with an active trough line along with the depression over the Bay, generally results in active monsoon conditions over the Maharashtra-Karnataka coasts, while the prevalence of an anticyclonic ridge pattern along the west coast at the time of the formation of the depression inhibits any increase in rainfall activity along these coasts.

Mukherjee, A. K. and B. P. Singh (1978). "Trends and periodicities in annual rainfall in monsoon areas over the Northern Hemisphere." Indian Journal of Meteorology, Hydrology & Geophysics, Delhi 29(1/2): 441-447.

Trends and periodicities in annual rainfalls in monsoon areas over the Northern Hemisphere have been examined. Stations selected for Southeast Asia are Colaba (Bombay), Trivandrum, and Colombo; for West Africa, they are Accra, Warri, Tower Hill (Freetown), and Dakar; and for Central America, Quito and Colon. The data were mostly collected from world weather records. For discerning long-term trends, a 25-point, ultra-low-pass, sine terminated filter was used to cut off all periods below 12 yr. In Southeast Asia, Colaba showed a rise between 1910 and 1955, and then a fall. Trivandrum does not show any significant variation, whereas the trend at Colombo is oscillatory. In West Africa, among the places south of the Sahara, Accra and Dakar do not show any trend, a general decrease is noticed at Tower Hill, and Warri shows an increase. In Central America, Colon shows an oscillatory trend, whereas Quito does not show any significant variation. There does not appear to be current decrease in the rainfall over the African monsoon countries and over India, as has been reported by Winstanley (1973). As regards periodicities, analysis was confined to 11- and 22-yr cycles. Besides being of physical significance, these two cycles have long enough periods to cause imbalance in drought-prone areas. These periods seem to be present everywhere, but they do not show systematic correlations with sun-spot numbers. The amplitudes on the oscillation do not exhibit any systematic dependence upon either latitude or longitude. Large differences were noticed even at neighboring places. Rainfall in these areas, because of its strong dependence upon local geography, is modulated strongly by other factors to show a poor correlation with sun-spot number.

Mullan, A. (1991). "Atmospheric circulation processes and features in the Southwest Pacific." Hay, John E.

This paper is intended to provide an overview of the atmospheric controls that affect the weather and climate of the island nations of the Southwest Pacific. The geographical focus is on the region to the north of the area dominated by the mid-latitude westerlies, and therefore will largely exclude consideration of Australia and New Zealand and also of Southeast Asia. The large-scale time-averaged circulation features important to the region include the sub-tropical high pressure belt, the easterly trade winds, the Intertropical Convergence Zone, the South Pacific Convergence Zone, the Monsoon Trough, and the Hadley and Walker circulations. Some island groups will experience different circulation regimes, with their associated weather systems, at different times of the year. Tropical cyclones are also a major feature of the climate of the region south of about 10 degrees S. Large variability is an intrinsic part of tropical climate. Variations from year to year have been attributed mainly to the El Nino-Southern Oscillation (ENSO) phenomenon, which involves an exchange of air between the tropical eastern Pacific and the Indian Ocean. ENSO changes produce marked rainfall anomalies in many Pacific Island groups through, among other things, a shift in the position of the South Pacific Convergence Zone. The occurrence of extreme events can also be altered through a shift in the preferred location of tropical cyclone tracks. An important influence on variability within a season is the 30-60 day oscillation. This feature appears as an eastward propagating wave pulse that modulates the intensity of convective systems in the equatorial Pacific, particularly west of the dateline.

Mullan, A. (1992). "Atmospheric circulation processes and features in the tropical Southwest Pacific." Weather and Climate, Wellington, New Zealand 12(2): 59-72.

This paper is intended to provide an overview of the atmospheric controls that affect the weather and climate of the island nations of the Southwest Pacific. The geographical focus is on the region to the north of the area dominated by the mid-latitude westerlies, and therefore will largely exclude consideration of Australia and New Zealand and also of Southeast Asia. The review is confined mostly to a discussion of surface features. The large-scale time-averaged circulation features important to the region include the subtropical high pressure belt, the easterly trade winds, the Intertropical Convergence Zone, the South Pacific Convergence Zone, the Monsoon Trough, and the Hadley and Walker circulations. Some island groups will experience different circulation regimes, with their associated weather systems, at different times of the year. Tropical cyclones are also a major feature of the climate of the region south of about 10 degrees S. Large variability is an intrinsic part of tropical climate. Variations from year to year have been attributed mainly to the El Nino-Southern Oscillation (ENSO) phenomenon, which involves an exchange of air between the tropical eastern Pacific and the Indian Ocean. ENSO changes produce marked rainfall anomalies in many Pacific island-groups through, among other things, a shift in the position of the South Pacific Convergence Zone. The occurrence of extreme events can also be altered through a shift in the preferred location of tropical cyclone tracks. An important influence on variability within a season is the 30-60-day oscillation. This feature appears as an eastward propagating wave pulse that modulates the intensity of convective systems in the equatorial Pacific, particularly west of the dateline.

Murakami, T. (1987). "Effects of the Tibetan Plateau." Chang, Chih Pei.

The results of investigations on four areas of the monsoon-related meteorology of the Tibetan Plateau are surveyed. The heat balance over the plateau is described for winter and summer. Regional aspects of the monsoon circulations developing over the Tibetan Plateau are summarized. The orographic influence of the planetary-scale monsoon circulation obtained observationally from the First GARP (Global Atmospheric Research Program) Global Experiment (FGGE) Level 3-a is described. Planetary-scale aspects of the monsoon circulations generated by numerical general circulation model experiments on orographic influences upon planetary-scale circulations are reviewed. Research activities and results obtained on the behavior of synoptic-scale disturbances of similar to 1000 km and a time scale of similar to 4-10 days developing over and around the Tibetan Plateau are surveyed. During winter, the mechanical blocking of the Tibetan Plateau appears to be important. In summer, the thermal effect of the Tibetan Plateau at the midtropospheric level ( identical with 5 km) appears to be equally as important as the Eurasian continent-Indian Ocean heat contrast at the Earth's surface in exciting the summer monsoon circulation. With regard to the orographic influence of the Tibetan Plateau upon the planetary-scale aspects of the monsoon circulations, it is noted that the Jan. mean velocity potential pattern at 200 mb is asymmetric about the Equator with prominent cross-equatorial divergent southerlies emanating from the Southern Hemisphere summer monsoon region (Indonesia-Northern Australia), eventually converging into the Northern Hemisphere convergent centers east of the Tibetan Plateau. In July, the Tibetan monsoon anticyclone at 200 mb is located similar to 50-80 degrees of longitude westward of the upper divergent center near the Indochina-Philippines region. The establishment of the low-level summer monsoon circulation is not primarily due to the orographic influence of the Tibetan Plateau, but is due mainly to radiative heating and cumulus condensation.

Nandargi, S. and O. N. Dhar (1998). "Cyclonic disturbances causing more than one rainstorm in India - a brief appraisal." The Journal of Meteorology, Wiltshire, England 23(227): 77-82.

In India, Cyclonic disturbances have been causing rainstorms during monsoon months of June to September. Normally, active disturbances cause one rainstorm while they move through the country. It has been observed that under favourable synoptic conditions more than one rainstorm can be caused especially when the movement of a low latitude west-moving cyclonic disturbance is in phase with east-moving westerly trough or a western disturbance in mid-latitudes. In such cases, the second rainstorm normally occurs in northwest India and if these happen towards the end of the monsoon season, severe floods in the rivers of northwest India occur. Depth-area-duration (DAD) statistics of some of the typical cases of multiple rainstorms have also been given here by way of illustration.

Nassor, A. and M. R. Jury (1997). "Intra-seasonal climate variability of Madagascar. Part 2: Evolution of flood events." Meteorology and Atmospheric Physics, Vienna, Austria 64(3-4): 243-254.

The meteorological structure of flood-producing weather systems affecting northern Madagascar is examined using ECMWF data. Daily rainfall in the austral summer is used to select 16 cases for a composite analysis of flood events in the period 1987-1992. Anomaly maps demonstrate a pair of convective vortices over SE Africa and the SW Indian Ocean which converge over northern Madagascar. Thermodynamic variables indicate an eastward shift of unstable moist conditions from SE Africa. A surge of monsoon northwesterlies and upper tropical easterlies are key features of flood producing systems over NW Madagascar.

Ninomiya, K. and T. Akiyama (1992). "Multi-scale features of Baiu, the summer monsoon over Japan and East Asia." Journal of the Meteorological Society of Japan, Tokyo, Japan 70(1B): 467-495.

This review paper summarizes the authors' recent studies on the Baiu, the summer monsoon, over the Japan Islands and the adjacent areas. The most important feature of the Baiu is the formation of the Baiu front, which is a long quasi-stationary precipitation belt extending from the southeastern foot of the Tibetan Plateau to Japan and further to the northwestern Pacific. The cold Baiu trough, the polar front and the Pacific subtropical anticyclone are the major large-scale circulation systems which have influence on the Baiu front. The frontogenesis and the generation of convective instability in the southwesterly flows along the west-northwest periphery of the Pacific subtropical anticyclone are the primary factors for the formation of the Baiu front. The structure of the Baiu front and the associated Baiu low-level jet stream, and the water vapor budget during the peak Baiu period are studied. The generation and release of the convective instability in the intense Baiu precipitation area are also analyzed. The features of the meso- alpha -scale disturbances in the Baiu frontal zone are studied by the spectral analysis of the relative vorticity field and the cloud amount. The meso- beta - and meso- gamma -scale fine structures within the meso- alpha -scale disturbances are demonstrated. The most outstanding feature of the Baiu is that the motions of many scales (planetary, synoptic, meso- alpha -, meso- beta - and meso- gamma -scales) are interacting with each other. The multi-scale aspects of the Baiu are stressed in this review paper.

Ninomiya, K. and T. Murakami (1987). "Early summer rainy season (Bai-u) over Japan." Chang, Chih Pei.

Research on the summer monsoon near Japan and its associated phenomena is reviewed on the basis of studies conducted from the 1960s to the present. The following aspects are treated: 1) general and climatological description of Bai-u; (the summer monsoon in the vicinity of Japan); 2) large-scale features of the bai-u front; 3) water vapor budget in the bai-u frontal zone; 4) structure of the bai-u front and the low-level jet stream, including structure of the time-averaged bai-u front and the bai-u front at a certain synoptic time; 5) medium-scale distances in the bai-u front--observational and theoretical studies and numerical experiments; 6) mesoscale precipitations in the bai-u front; and 7) influence of the Pacific subtropical anticyclone and tropical maritime air mass upon the bai-u front.

Niranjan, S., S. R. Kalsi, et al. (1997). "Meteorological sevices provided through INSAT." Journal of Spacecraft Technology, Bangalore, India 7(1): 24-29.

Satellite technology plays an important role in weather forecasting. Satellite data has proved to be useful for identifying potential areas of heavy precipitation and giving timely warnings of floods. Satellite data products provide useful inputs to the Numerical Weather Prediction (NWP) models. The INSAT cloud imagery data and the derived products now form an integral and important part of aids/data available to the forecasters for operational and research related applications in meteorology. Some of the services operated by Indian Meteorological Department (IMD) using the television broadcast capabilities of INSAT like the Cyclone Warning Dissemination System (CWDS) have been found to be useful by the field offices of IMD in warning coastal population against impending disastrous weather such as tropical cyclones. Here we present a brief history of satellite meteorology at IMD and review the contributions and applications of satellite technology to operational meteorological analysis and weather forecasting. Section headings include; Qualitative weather analysis; Western disturbances; Local severe storms; Monsoon phenomena; Tropical cyclones; Satellite derived products; Cloud Motion Vectors (CMVs); Sea Surface Temperatures (SSTs); Outgoing Longwave Radiation (OLR); Quantitative Precipitation Estimates (QPEs). Important services provided through INSAT Broadcasting capabilities are briefly reviewed and include the Cyclone Warning Dissemination System (CWDS), Meteorological Data Dissemination (MDD) system, and Data Collection Platforms (DCPs). The INSAT based cyclone warning dissemination system provides quick and reliable dissemination of weather warnings about impending disasters from approaching cyclones much in advance and this has been useful to user agencies such as the State Governments.

Nitta, T. and K. Nasuda (1981). "Observational study of a monsoon depression developed over the Bay of Bengal during summer MONEX." Meteorological Society of Japan, Tokyo, Journal 59(5): 672-682.

Three-dimensional structure of a monsoon depression that developed over the Bay of Bengal during summer MONEX is examined by the use of aircraft dropwindsonde and conventional upper air observations. Wind, temperature, and relative humidity data are interpolated objectively at 1 degrees -lat./long. grid points over the area of 11-24 degrees N and 80-93 degrees E and at 25-mb pressure levels from the surface to the 500-mb level for the period July 3-8, 1979. The depression formed over the Bay of Bengal at about 19 degrees N and 90 degrees E on July 6, moved westward with about 2 degrees -day super(-) super(1) speed, and reached a coastline of India on July 8. The developed depression has the maximum vorticity of about 1.5 x 10 super(-) super(4) sec super(-) super(1) and a warm core slightly to the east of the depression center. Horizontal convergence and rising motion occur to the west of the depression center, where active convective clouds exist. The horizontal axis of the depression is inclined from southwest to northeast. The depression transports heat and momentum northward and gains its kinetic energy from the mean zonal flow. The analysis during the preformation period shows that large positive vorticity of about 5 x 10 super(-) super(5) sec super(-) super(1) exists in the area over the bay which is close to the area of depression formation. This large positive vorticity is caused by both the existence of a weak trough and the meridional gradient of the zonal flow. The latitude-height distribution of the zonal wind, averaged over the Bay of Bengal for the preformation period, shows that the necessary condition for instability of the zonal flow is satisfied. A stability analysis of the zonal flow averaged in the lower troposphere below 500 mb indicates that the flow is barotropically unstable, with the maximum growth rate at about 3500 km. The unstable wave has several characteristic features similar to those observed.

Nogues-Paegle, J. E. and Z. Zhen (1987). "Australian subtropical jet during the second observing period of the Global Weather Experiment." Journal of the Atmospheric Sciences, Boston 44(16): 2277-2289.

The upper level circulation of the Southern Hemisphere winter is characterized by two distinct zonal wind maxima: a subtropical jet found in the vicinity of Australia and the western Pacific Ocean, and a polar jet, which maximizes in the Indian Ocean in the 45-55 degrees S lat. belt. This paper describes the global characteristics of the atmosphere for cases with strong subtropical jets during the 1979 Northern Hemisphere summer. Such cases are shown to coexist with episodes of strong release of latent heat in the Northern Hemisphere at similar longitudes. Gridded analyses of the Global Weather Experiment produced by the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration are used to obtain composites of atmospheric motions prior to the onset and during active episodes of the Asian Monsoon. Projections of these motions into the normal modes of a linearized primitive equation model about a basic state at rest are presented to isolate observed global flow characteristics. Relative contributions from internal and external modes are shown as well as those from gravity, Rossby, and equatorially trapped modes. Results indicate that active hemispheric interactions take place in the longitudes of the Southern Hemisphere subtropical jet and are accomplished by motions possessing the horizontal structure of internal gravity modes. The subtropical and polar jets have very different vertical structures, projecting mostly in internal and external modes, respectively. Accelerations of the subtropical jet occur because of changes in both the internal and external Rossby modes, with the latter contributing most to these accelerations.

Oliphant, A. J., A. P. Sturman, et al. (2001). "The evolution and structure of a tropical island sea/land-breeze system, northern Australia." Meteorology and Atmospheric Physics 78(1-2): 45-59.

This paper is concerned with sea/land-breeze systems over relatively flat tropical islands to the north of continental Australia. The purpose of this study is to contribute to the relatively small body of knowledge on tropical island sea/land-breeze systems in this region and to highlight their particular characteristics. The evolution and structure of coastal circulations over the Tiwi Islands, northern Australia are examined using observations made during the Maritime Continent Thunderstorm Experiment (MCTEX), November/December 1995. During the transition period between dry and wet (monsoon) seasons, strong diurnal surface heating dominates the local meteorology. Thermally modified pressure differences across the coastline are seen to control the timing, direction and intensity of local winds. The evolution and structure of the resulting circulations appear to be affected greatest by tropospheric stability and friction, while the Coriolis force, synoptic winds and topography are of much less importance in this case. Consequently, even small differences in surface properties seem to produce strong and well defined local wind circulations. The depth of the sea breeze averaged 1200 m, while the land breeze was considerably shallower (290 m). Return flows were evident in both circulations, although better defined in land breeze cases. Day to day variation in vertical structure was considerable and appeared to be controlled by stability in the lower troposphere. Spatial patterns of surface temperature, pressure and wind show formation of an island heat low by day and a cool high pressure centre at night, resulting in island scale convergence and divergence, respectively.

Park, C.-K. and S. D. Schubert (1997). "On the nature of the 1994 East Asian summer drought." Journal of Climate, Boston, MA 10(5): 1056-1070.

East Asian countries experienced record-breaking heat waves and drought conditions during the summer monsoon season of 1994. This study documents the large-scale circulation associated with the drought and suggests a forcing mechanism responsible for the anomalous evolution of the East Asian monsoon. The results, based on Goddard Earth Observing System (GEOS) global assimilated data for 1985-94, indicate that the absence of monsoon rainfall during July 1994 over central China and the southern parts of Korea and Japan is due to the unusually early development of the climatological upper-level anticyclonic flow east of the Tibetan Plateau. The anomalous July anticyclonic circulation over the East Asian-northwestern Pacific region and the cyclonic circulation over the subtropical western Pacific, which are more typical of August, acted to reduce the moisture supply from the western Pacific and the Indian Ocean leading to suppressed rainfall over East Asia. The similarity of the July 1994 East Asian circulation anomalies to the climatological July to August change in these quantities suggests that the anomalies may be viewed as an acceleration of the seasonal cycle in which the circulation transitions to August conditions earlier than normal. Neither tropical nor middle latitude SST anomalies provide a viable forcing mechanism for the 1994 East Asian circulation anomalies: the tropical anomalies are weak and the middle latitude anomalies, while stronger, appear to be primarily a response to atmospheric forcing, though they may feed back to reinforce the atmospheric anomalies. It is suggested, instead, that the anomalous circulation is primarily the result of an orographic forcing associated with zonal wind changes over Tibet. The zonal wind change, characterized by an anomalous northward shift of the East Asian jet is, in turn, tied to unusually persistent stationary waves extending from northern Europe, which developed prior to the onset of the East Asian anticyclone. Several other occurrences of atmospheric anomalies similar in structure (though weaker in amplitude) to the July 1994 anomalies are found in the previous nine summers, suggesting the operative mechanism is not unique to 1994. Such a mechanism appears to operate both for the climatological development of the ridge and for the occurrences of similar anomalies in previous summers: in the former the northward shift of the jet over Tibet is a reflection of climatological seasonal change in the zonal wind, while in the latter, the shift is the result of anomalies similar in structure to the 1994 European-Asian wave pattern. The indirect role of the Eurasian waves in the development of the East Asian circulation anomalies suggests that useful monthly and longer predictions of the monsoon rests, not only on our ability to predict the occurrence of these waves, but also on our ability to properly model their interaction with orography.

Paul, D. K., S. P. Ghanekar, et al. (1995). "Wind profiles in the boundary layer over Kharagpur associated with synoptic scale systems." Proceedings, Bangalore, India 104(2): 317-326.

Doppler sodar wind data for the boundary layer over Kharagpur obtained during MONTBLEX-1990 at a height interval of 30 m from surface up to 1500 m have been analysed for the periods when intense synoptic scale disturbances from north Bay of Bengal moved along the eastern end of the monsoon trough. The variation in the vertical wind profile in the lower boundary layer over Kharagpur during the passage of synoptic scale disturbances has been discussed in the paper. The analysis indicates that the mean winds over Kharagpur veered with height in the lower boundary layer near the surface suggesting divergence over Kharagpur when the system lay south /southwest of the station. No such veering has been noticed when the centre of the system lay very close to the station.

Pearce, R. P. (1990). "Scientific assessment of some important research fields of tropical meteorology." Geneva, Switzerland, World Meteorological Organization 40.

This document is an update of a scientific assessment made of the state of knowledge of some important research fields in tropical meteorology. Attention is given to tropical cyclones; and to monsoons, considering global scale features and regional features of the Asian summer and winter monsoons. Other areas covered include tropical rain-bringing systems other than tropical cyclones and monsoon disturbances, discussing the ITCZ, West African disturbance lines (squall lines), easterly waves, and other systems; interaction between tropical and mid-latitude weather systems, discussing mid-latitude systems affecting the SW Pacific, winter monsoon cold surges across SE Asia, `western disturbances' over India, interaction with systems in lower level westerlies, western disturbances and induced lows, low level trough in the westerlies, interaction with troughs in the upper tropospheric westerlies, application of the IPV analysis technique to the study of tropical-mid-latitude interactions, and the penetration of cold fronts across North Africa, into Brazil, and into southern Africa. For each of these topics, attention is given to the state of knowledge of the subject, economic significance, scientific questions which remain to be answered, and some aspects to which early attention should be directed. Tropical droughts are also examined; as is numerical weather prediction in the tropics, considering the status of model development, accuracy of existing models, the nature and sources of model errors, and numerical prediction of tropical cyclones.

Pfister, L., K. R. Chan, et al. (1993). "Gravity waves generated by a tropical cyclone during the STEP tropical field program: a case study." Journal of Geophysical Research, Washington, DC 98(D5): 8611-8638.

Overflights of a tropical cyclone during the Australian winter monsoon field experiment of the Stratosphere-Troposphere Exchange Project (STEP) show the presence of two mesoscale phenomena: a vertically propagating gravity wave with a horizontal wavelength of about 110 km and a feature with a horizontal scale comparable to that of the cyclone's entire cloud shield (wavelength of 250 km or greater). The larger feature is fairly steady, though its physical interpretation is ambiguous. The 110-km gravity wave is transient, having maximum amplitude early in the flight and decreasing in amplitude thereafter. Its scale is comparable to that of 100- to 150-km-diameter cells of low satellite brightness temperatures within the overall cyclone cloud shield; these cells have lifetimes of 4.5 to 6 hours. Aircraft flights through the anvil show that these cells correspond to regions of enhanced convection, higher cloud altitude, and upwardly displaced potential temperature surfaces. A three-dimensional transient linear gravity wave simulation shows that the temporal and spatial distribution of meteorological variables associated with the 110-km gravity wave can be simulated by a slowly moving transient forcing at the anvil top having an amplitude of 400-600 m, a lifetime of 4.5-6 hours and a size comparable to the cells of low brightness temperature. The forcing amplitudes indicate that the zonal drag due to breaking mesoscale transient convective gravity waves is definitely important to the westerly phase of the stratopause semiannual oscillation and possibly important to the easterly phase of the quasi-biennial oscillation. There is strong evidence that some of the mesoscale gravity waves break below 20 km as well. The effect of this wave breaking on the diabatic circulation below 20 km may be comparable to that of above-cloud diabatic cooling.

Plessing, P. and A. K. Mukherjee (1978). "Lowering of the ozone layer during the formation of tropical cyclones and depressions." Zeitschrift fuer Meteorologie, Berlin 28(5): 270-273.

During the international Monsoon-77 experiment, electronic ozone sondes were operated in the monsoon area of southern India. Observations show that, during the development of tropical cyclones, deviations from the usual vertical distribution of the atmospheric ozone occur. The displacement of the layer with the maximum ozone partial pressure into the lower stratosphere permits the assumption to be made that there are dynamically produced strong downward motions in the stratosphere within tropical cyclones. The authors present a model to illustrate these phenomena.

Popovic, J. M. and R. Plumb (2001). "Eddy shedding from the upper-tropospheric Asian monsoon anticyclone." Journal of the Atmospheric Sciences, Boston, MA 58(1): 93-104.

The authors investigate the transient behavior of the Asian monsoon anticyclone in the summertime upper troposphere for the four northern summers 1987-90. The evolution of potential vorticity near the tropopause shows the development of westward migrating anticyclones breaking off from the main anticyclone a few times each summer. These disturbances are relatively shallow, being confined to the upper troposphere.

Pradhan, R., U. K. De, et al. (1995). "A study in search of interconnection between surface parameters and surrounding synoptic and subsynoptic features." Advances in Atmospheric Sciences, Beijing, China 12(4): 475-486.

The paper reveals that the variations in parameters like u, the scaling velocity and theta . The scaling temperature during the various phases of monsoon might be linked with subsynoptic features. The rise in u is mainly connected with the presence of lower tropospheric cyclonic vorticity over a subsynoptic scale of the site. However the variations in theta sub(*) . is mainly linked with the various phases of monsoon and theta shows a sharp rise in presence of low level convective cloud. Besides the correlation studies of u and u, theta sub(v) and theta sub(v) , theta sub(v) - theta sub(v) sub(0) and theta sub(v) are undertaken. The correlation between, theta sub(v) and theta sub(v) is poor. In other two cases correlations are good. Besides delta u/ delta u has shown good coefficient of variation values within the zeta range.

Prakasa Rao, G. S. (1975). "Synoptic features during the break monsoon in 1965 and 1966." Indian Journal of Meteorology, Hydrology and Geophysics, Delhi 26(4): 535-537.

A prolonged break of 12 days in Aug. (4th-15th) and 10 days in July (2nd to 11th) occurred during 1965 and 1966, respectively. An examination of zonal and meridional components of wind was made during the break periods of 1965 and 1966. Zonal winds at the 150-mb level for Trivandrum, Madras, Bombay, and Nagpur are shown in a graph. During the break periods, easterlies continued to be strong and remained at the same latitude (8-13 degrees N) as in strong monsoon periods. The meridional circulation during the break period is compared with that of the mean meridional circulation. The easterlies descended and penetrated to 700 mb, and the strongest easterlies at 150 mb continued to be observed at their normal latitude of occurrence.

Prasad, K. and S. Sen (1981). "Flood meteorology of Ganga basin in Bihar: a synoptic analogue study." Mausam, New Delhi 32(4): 415-424.

A detailed survey has been made from available records of all past synoptic situations that resulted in heavy rainfall in different subcatchments of the Ganga basin in Bihar in different months of the monsoon season. Most of these spells are associated with either a low-pressure system or a break monsoon condition. While the heavy rain associated with break condition is confined to the immediate vicinity of the monsoon trough, the effect of a low-pressure system extends beyond its location. It has been possible to delineate an area for each month and each individual subcatchment where there is a low-pressure system which contains the risk of heavy rainfall in that particular subcatchment. This area has been termed the risk zone for the subcatchment.

Prasad, K. and A. K. Sen Sarma (1978). "Synoptic study of July 1971 and August 1975 floods in River Sone." Indian Journal of Meteorology, Hydrology & Geophysics,, Delhi 29(4): 752-754.

The Sone River experienced serious flood conditions in the southwest monsoon periods of 1971 and 1975. In both cases, the attendant meteorological phenomenon was slow movement-stagnation of Bay of Bengal depressions over southeast Uttar Pradesh and adjoining northeast Madhya Pradesh, an area northeast of the upper Sone catchment. This paper examines the situations leading to the slow movement-stagnation of monsoon depressions of July 1971 and Aug. 1975. It is traced to the development of quasi-stationary disturbances in middle latitude westerlies.

Prasad, R. and S. V. Datar (1989). "Intensification and persistence of kharif agricultural drought during 1987." Mausam, New Delhi 40(3): 269-274.

The Weekly Aridity Index (AI) based on Thornthwaite's water balance technique has been used to study the intensification and persistence of kharif agricultural drought during the southwest monsoon season of 1987, in 33 meteorological subdivisions of India, by adopting a simple criterion. The periods and areas of maximum intensification and persistence have been identified. The analysis revealed that intensification occurred in only seven subdivisions, confined mostly to the northern and western regions of the country. Persistence was invariably associated with intensification, whereas reverse observation was not perceptible. Mixed mode drought persistence was maximum in the Rajasthan and Gujarat regions. A comparison with meteorological drought, however, revealed that either intensification or persistence of agricultural drought occurred in those subdivisions affected by severe meteorological drought.

Pribish, Y. (1981). "Analysis of the tropospheric structure over the Indian Ocean at the first stage of the Monsoon-77 expedition from the data of the research weather ship Priliv." Akademiya Nauk SSSR, Moscow, Mezhduvedomstvennyy Geofizicheskiy Komitet, Meteorologicheskiye Issledovaniya(24): 65-70.

Space-time sections of temperature, humidity, and wind fields are drawn for the period of May 27-June 20, 1977, from the data of aerological observations made by the R/N Priliv. This paper discusses the influence of the ITCZ (intratropical convergence zone) of the Southern Hemisphere at 2 degrees S. It is established that, when western streams north of the Equator were traced to an altitude of 5-7 km in the premonsoon period, their upper boundaries reached 8-10 km after the burst of the monsoon. After the burst of the monsoon in the region of 10 degrees N, the second layer reducing the passage of convective streams was observed at an altitude of 6-7 km.

Pudov, V. D. and S. A. Petrichenko (1988). "Surface temperature of the South China Sea and tropical cyclones." Meteorologiya i Gidrologiya, Moscow, Dec(12): 118-121.

Experimental data are presented on the surface temperatures of the South China Sea, on the characteristics of the spatial scales, and on the mean square values of their variability. The data were collected in the period July 2-14, 1987. Coastal upwelling produced by the action of the southwest monsoon was found in the southwestern part of the sea. The trajectories of tropical cyclones on the surface of the sea over a 23-yr period were analyzed. The coastal upwelling is a distinctive natural protection of the territory of South Vietnam against the effect of tropical cyclones.

Puri, K. (1990). "Tropical numerical weather prediction studies for the 1987 Australian summer monsoon." Mausam, New Delhi, India 41(2): 257-264.

The performance of the ECMWF analysis-forecast system in depicting the main features of the 1987 Australian monsoon is described. The features include the mean circulation for the period and the onset and active/break periods of the monsoon. The model is successful in predicting the mean features up to 3 days ahead with the main deficiency being the marked weakening of the upper level divergent circulation with time. The analyses successfully depict most features of the monsoon circulation. Although the model is able to forecast onset up to about 1 day ahead and the subsequent episodes up to about 2 days ahead, there is a tendency in the model forecasts to weaken the low level westerly winds with time.

Puri, K., N. E. Davidson, et al. (1992). "Numerical modelling of severe weather in the tropics: problems and possible solutions." Jasper, J. D. and Meighen, P. J.