A study on drought features of the Indian summer monsoon 2002

In this paper, a diagnostic study is carried out with global analysis data sets to determine how the large scale atmospheric circulation affecting the anomalous drought of the Indian summer monsoon 2002. The daily analysis obtained from National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) for the month of July is used to investigate the mean circulation characteristics and the large scale energetics over the Indian monsoon domain. Examination of rainfall revealed that the summer monsoon (JJAS) rainfall of 2002 over India is 22% below normal in which the large deficit of 56% below normal rainfall in July. The recent past drought during summer season of 2004 and 2009 are 12 and 23%, respectively, below normal rainfall. The large deficit of rainfall in 2009 is from the June month with 48% below normal rainfall, where as 2004 drought contributed from July (19%) and August (24%). Another significant facet of the rainfall in July 2002 is lowest ever recorded in the past 138 years (1871–2008). The circulation features illustrated weak low level westerly wind at 850 hPa (Somali Jet) in July during large deficit rainfall years of 1987 and 2002 with a reduction of about 30% when compared with the excess and normal rainfall years of 1988 and 2003. Also, tropical easterly jet at 150 hPa reduced by 15% during the deficit rainfall year of 2002 against the excess rainfall year of 1988. Both the jet streams are responsible for low level convergence and upper level divergence leading to build up moisture and convective activity to sustain the strength of the monsoon circulation. These changes are well reflected in reduction of tropospheric moisture profile considerably. It is found that the maximum number of west pacific cyclonic system during July 2002 is also influenced for large deficit rainfall over India. The dynamic, thermodynamic and energetic clearly show the monsoon break type situation over India in the month of July 2002 resulting less convective activity and the reduction of moisture. The large diabatic heating, flux convergence of heat and moisture over south east equatorial Indian Ocean are also responsible for drought situation in July 2002 over the Indian region.     

Fluctuations of Tropical Easterly Jet during contrasting monsoons over India: A GCM study

Summary  The fluctuations of intensity of the Tropical Easterly Jet (TEJ) and its association with the Indian summer monsoon rainfall have been examined using the diagnostics from NCEP/NCAR (National Centre for Environmental Prediction/National Centre for Atmospheric Research) reanalyses project for the period 1986 to 1994. The intensity of TEJ is found to be well correlated with India summer monsoon rainfall. The TEJ is weaker/stronger during the El Ni?o/La Ni?a year of 1987/1988 and is associated with deficient (excess) summer monsoon rainfall over India. A numerical study was carried out for the same period using the Centre for Ocean-Land-Atmosphere studies General Circulation Model (COLA GCM, T30L18) with observed Sea-Surface Temperature (SST). The GCM simulates the TEJ with reasonable accuracy. The strong interannual variability of TEJ during the El Ni?o/La Ni?a years of 1987/1988 are well simulated in the GCM. Like observations, the intensity of the TEJ is positively correlated with the summer monsoon rainfall over India in the model simulation. The intensity of Tibetan anticyclone and diabatic heating over the Tibetan Plateau diminished during the El Ni?o-year of 1987. The divergence centre in the upper troposphere associated with Asian monsoon becomes weaker and shifts eastward during the weak monsoon season of 1987. However, the opposite happens for the strong monsoon season of 1988. Also the middle and upper tropospheric meridional temperature gradient between the Tibetan High and Indian Ocean region decreased (increased) during the weak(strong) monsoon season of 1987 (1988). Received May 27, 1999/Revised March 20, 2000     

Influence of convective parameterization on the systematic errors of Climate Forecast System (CFS) model over the Indian monsoon region from an extended range forecast perspective

This study investigates the influence of Simplified Arakawa Schubert (SAS) and Relax Arakawa Schubert (RAS) cumulus parameterization schemes on coupled Climate Forecast System version.1 (CFS-1, T62L64) retrospective forecasts over Indian monsoon region from an extended range forecast perspective. The forecast data sets comprise 45 days of model integrations based on 31 different initial conditions at pentad intervals starting from 1 May to 28 September for the years 2001 to 2007. It is found that mean climatological features of Indian summer monsoon months (JJAS) are reasonably simulated by both the versions (i.e. SAS and RAS) of the model; however strong cross equatorial flow and excess stratiform rainfall are noted in RAS compared to SAS. Both the versions of the model overestimated apparent heat source and moisture sink compared to NCEP/NCAR reanalysis. The prognosis evaluation of daily forecast climatology reveals robust systematic warming (moistening) in RAS and cooling (drying) biases in SAS particularly at the middle and upper troposphere of the model respectively. Using error energy/variance and root mean square error methodology it is also established that major contribution to the model total error is coming from the systematic component of the model error. It is also found that the forecast error growth of temperature in RAS is less than that of SAS; however, the scenario is reversed for moisture errors, although the difference of moisture errors between these two forecasts is not very large compared to that of temperature errors. Broadly, it is found that both the versions of the model are underestimating (overestimating) the rainfall area and amount over the Indian land region (and neighborhood oceanic region). The rainfall forecast results at pentad interval exhibited that, SAS and RAS have good prediction skills over the Indian monsoon core zone and Arabian Sea. There is less excess rainfall particularly over oceanic region in RAS up to 30 days of forecast duration compared to SAS. It is also evident that systematic errors in the coverage area of excess rainfall over the eastern foothills of the Himalayas remains unchanged irrespective of cumulus parameterization and initial conditions. It is revealed that due to stronger moisture transport in RAS there is a robust amplification of moist static energy facilitating intense convective instability within the model and boosting the moisture supply from surface to the upper levels through convergence. Concurrently, moisture detrainment from cloud to environment at multiple levels from the spectrum of clouds in the RAS, leads to a large accumulation of moisture in the middle and upper troposphere of the model. This abundant moisture leads to large scale condensational heating through a simple cloud microphysics scheme. This intense upper level heating contributes to the warm bias and considerably increases in stratiform rainfall in RAS compared to SAS. In a nutshell, concerted and sustained support of moisture supply from the bottom as well as from the top in RAS is the crucial factor for having a warm temperature bias in RAS.     

A comparison of reanalyses in the tropical stratosphere. Part 1: thermal structure and the annual cycle

 An intercomparison of the thermal structure and the annual cycle in the tropical lower stratosphere of two reanalysis datasets is presented. These are from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and the European Centre for Medium Range Weather Forecasts (ECMWF Re-Analysis: ERA). Generally, the ERA data are coldest and in better agreement with radiosonde observations; this is particularly apparent at 100 hPa where there is also a strong geographic bias, the maximum differences (more than 4 K) occurring over the southern Pacific and the Indian Ocean, with much smaller (sometimes reversed) differences over land. The NCEP temperatures are biased towards satellite-derived values, while the ERA data resolve the low tropopause temperatures much better. The lower ERA temperatures have important implications for the cross-tropopause exchange of water vapor. The meridional-height structure of the annual cycles agree quite well, but the amplitude in the ERA data is about 50% stronger than in NCEP at 70 hPa (in better agreement with previous studies) and weaker at lower pressures. As in previous studies, an anticorrelation is found between the tropical and extratropical temperatures of the reanalyses. The mean meridional flow at the equator is northward all year at all stratospheric levels in the NCEP data, implying a mass transport from the Southern to the Northern Hemisphere; in the ERA data the expected annual cycle (flow from summer to winter) is reproduced with very small annual mean exchange. Received: 17 June 1997/Accepted: 17 December 1997     

Western Himalayan snow cover and Indian monsoon rainfall: A re-examination with INSAT and NCEP/NCAR data

Summary ?This study presents the monthly climatology and variability of the INSAT (Indian National Satellite) derived snow cover estimates over the western Himalayan region. The winter/spring snow estimates over the region are related to the subsequent summer monsoon rainfall over India. The NCEP/NCAR data are used to understand the physical mechanism of the snow-monsoon links. 15 years (1986–2000) of recent data are utilized to investigate these features in the present global warming environment. Results reveal that the spring snow cover area has been declining and snow has been melting faster from winter to spring after 1993. Connections between snow cover estimates and Indian monsoon rainfall (IMR) show that spring snow cover area is negatively related with maximum during May, while snow melt during the February–May period is positively related with subsequent IMR, implying that smaller snow cover area during May and faster snow melt from winter to spring is conducive for good monsoon activity over India. NCEP/NCAR data further shows that the heat low over northwest India and the monsoon circulation over the Indian subcontinent, in particular the cross-equatorial flow, during May are intensified (weakened) when the snow cover area during May is smaller (extensive) and snow melts faster (slower) during the February–May period. The well-documented negative relationship between winter snow and summer rainfall seems to have altered recently and changed to a positive relationship. The changes observed in snow cover extent and snow depth due to global warming may be a possible cause for the weakening winter snow–IMR relationship. Received January 15, 2002; revised May 5, 2002; accepted June 23, 2002     

索马里跨赤道气流对南海夏季风爆发的重要作用

通过分析NCEP/NCAR多年再分析资料,清楚地揭露了南海夏季风爆发与索马里跨赤道南风气流建立之间的重要关系.对应南海夏季风爆发,总是已先期在赤道印度洋地区有西风加强和索马里跨赤道南风气流的建立;而且,若南海夏季风爆发偏早(晚),赤道印度洋地区西风的加强和索马里跨赤道南风气流的建立也偏早(晚).可以认为,索马里跨赤道南风气流的稳定建立是南海夏季风爆发的重要物理机制之一,它的建立导致赤道印度洋地区西风的持续加强和向东扩展,并最终在南海地区形成西南气流.     

东亚季风环流演变的主要模态及其与中国东部降水异常的联系

利用美国国家环境预报中心和国家大气研究中心(NCEP/NCAR)再分析环流资料、美国国家海洋和大气管理局(NOAA)重构的海温资料和中国国家气象信息中心(NMIC)整理的752个测站降水资料,对东亚地区季风环流季节演变主要模态及其与中国东部降水异常的关系进行了分析。结果表明,东亚地区850hPa季风环流季节演变存在两个主要模态,第一模态主要受热带印度洋海温和赤道东太平洋海温偏低背景下印度洋偶极(IOD)演变过程控制;第二模态主要受赤道东太平洋ENSO循环和IOD演变控制。对应第一模态,夏季华北多雨,长江流域少雨;对应第二模态,夏季华北、长江流域多雨,淮河、华南少雨。近50年两模态发生了明显改变,与降水变化有很好的对应关系。     

Relationship Between East Asian Winter Monsoon and Summer Monsoon

Using National Centers for Environmental Prediction/National Centre for Atmospheric Research(NCEP/NCAR) reanalysis data and monthly Hadley Center sea surface temperature(SST) data,and selecting a representative East Asian winter monsoon(EAWM) index,this study investigated the relationship between EAWM and East Asian summer monsoon(EASM) using statistical analyses and numerical simulations.Some possible mechanisms regarding this relationship were also explored.Results indicate a close relationship between EAWM and EASM:a strong EAWM led to a strong EASM in the following summer,and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in the tropical Indian Ocean and the South China Sea,and on the equatorial atmospheric thermal anomalies at both lower and upper levels.Through these impacts,the EAWM influences the land-sea thermal contrast in summer and the low-level atmospheric divergence and convergence over the Indo-Pacific region.It further affects the meridional monsoon circulation and other features of the EASM.Numerical simulations support the results of diagnostic analysis.The study provides useful information for predicting the EASM by analyzing the variations of preceding EAWM and tropical SST.     

南海夏季风期间水汽输送的气候特征

通过分析NCEP/NCAR 1973～1998年(共26年)4～8月的再分析比湿场和风场资料,研究了南海夏季风期间的水汽输送特征.夏季,东亚上空水汽水平输送特征在各月有很大差异,这是夏季风环流系统演变的结果.孟加拉湾南部地区是中国长江中下游和南海地区重要的水汽源地,来自上游孟加拉湾南部地区的水汽输送对南海季风的爆发具有重要意义.经向水汽输送主要有利于20～30°N之间华南地区的水汽辐合.从总的收支看,南海地区是一个水汽汇区.南海季风爆发早晚年的水汽输送通道存在明显差别.在爆发偏早年,从赤道印度洋到南海地区的输送通道建立早且维持时间长,4～5月南海易成为水汽辐合区;在偏晚年,南海地区水汽则是辐散的,不利于形成季风性降水.南海季风爆发早晚年与长江中下游旱涝年的水汽输送有一定联系.     

Simulation of West African monsoon using the RegCM3. Part I: Model validation and interannual variability

Summary The West African monsoon oscillates each year with remarkable regularity but the interannual variability associated with the monsoon is not fully understood although much progress has been made in recent years. This study examines and evaluates the mean state and the interannual variability of the West African climate as simulated by the International Centre for Theoretical Physics (ICTP) Regional Climate Model version 3 (RegCM3) over the period 1979 through 1990 using the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data as lateral boundary conditions. Our analysis shows that the averaged rainfall over the region is well represented by the model and demonstrates considerable skill in reproducing the extreme rainfall regimes. There is however a tendency to overestimate rainfall amounts along the Guinean coast, particularly around mountainous areas, and to underestimate it over the Soudano-Sahel. The increased rainfall along the coast is due to an enhanced low-level convergence of the moist southwesterly winds along the coast leading to a reduction of the moisture content in the atmosphere. The decrease over the Soudano-Sahel could be associated with the weakening of the land–sea temperature gradient and hence the decrease in the low level southerly flows. The spatial and temporal variations in temperature are well captured by the model except for slightly cold bias over the coastal region due to an overestimation of precipitation.     

Asian summer monsoon prediction in ECMWF System 4 and NCEP CFSv2 retrospective seasonal forecasts

The seasonal prediction skill of the Asian summer monsoon is assessed using retrospective predictions (1982–2009) from the ECMWF System 4 (SYS4) and NCEP CFS version 2 (CFSv2) seasonal prediction systems. In both SYS4 and CFSv2, a cold bias of sea-surface temperature (SST) is found over the equatorial Pacific, North Atlantic, Indian Oceans and over a broad region in the Southern Hemisphere relative to observations. In contrast, a warm bias is found over the northern part of North Pacific and North Atlantic. Excessive precipitation is found along the ITCZ, equatorial Atlantic, equatorial Indian Ocean and the maritime continent. The southwest monsoon flow and the Somali Jet are stronger in SYS4, while the south-easterly trade winds over the tropical Indian Ocean, the Somali Jet and the subtropical northwestern Pacific high are weaker in CFSv2 relative to the reanalysis. In both systems, the prediction of SST, precipitation and low-level zonal wind has greatest skill in the tropical belt, especially over the central and eastern Pacific where the influence of El Nino-Southern Oscillation (ENSO) is dominant. Both modeling systems capture the global monsoon and the large-scale monsoon wind variability well, while at the same time performing poorly in simulating monsoon precipitation. The Asian monsoon prediction skill increases with the ENSO amplitude, although the models simulate an overly strong impact of ENSO on the monsoon. Overall, the monsoon predictive skill is lower than the ENSO skill in both modeling systems but both systems show greater predictive skill compared to persistence.     

Impact of domain size on the simulation of Indian summer monsoon in RegCM4 using mixed convection scheme and driven by HadGEM2

In this study, a smaller domain over India alone and a larger South Asia (SA) domain have been used in the Regional Climate Model version 4.2 (RegCM4.2) to examine the effect of the domain size on the Indian summer monsoon simulations. These simulations were carried out over a period of 36 years at 50 km horizontal resolution with the lateral boundary forcings of the UK Met Office Hadley Centre Global Circulation Model Version 2.0. Results show that the Indian summer monsoon rainfall is significantly reduced when the domain size for the model integration is reduced from SA to the Indian domain. In case of SA domain simulation, the Equitable Threat Scores have higher values in case of very light, light and moderate rainfall events than those in case of the Indian domain simulation. It is also found that the domain size of model integration has dominant impact on the simulated convective precipitation. The cross-equatorial flow and the Somali Jet are better represented in the SA simulation than those in the Indian domain simulation. The vertically integrated moisture flux over the Arabian Sea in the SA domain simulation is close to that in the NCEP/NCAR reanalysis while it is underestimated in the Indian domain simulation. It is important to note that when RegCM4.2 is integrated over the smaller Indian domain, the effects of the Himalayas and the moisture advection from the Indian seas are not properly represented in the model simulation and hence the monsoon circulation and associated rainfall are underestimated over India.     

Simulation of Indian summer monsoon circulation and rainfall using RegCM3

Summary The Regional Climate Model RegCM3 has been used to examine its suitability in simulating the Indian summer monsoon circulation features and associated rainfall. The model is integrated at 55 km horizontal resolution over a South Asia domain for the period April–September of the years 1993 to 1996. The characteristics of wind at 850 hPa and 200 hPa, temperature at 500 hPa, surface pressure and rainfall simulated by the model over the Indian region are examined for two convective schemes (a Kuo-type and a mass flux scheme). The monsoon circulation features simulated by RegCM3 are compared with those of the NCEP/NCAR reanalysis and the simulated rainfall is validated against observations from the Global Precipitation Climatology Centre (GPCC) and the India Meteorological Department (IMD). Validation of the wind and temperature fields shows that the use of the Grell convection scheme yields results close to the NCEP/NCAR reanalysis. Similarly, the Indian Summer Monsoon Rainfall (ISMR) simulated by the model with the Grell convection scheme is close to the corresponding observed values. In order to test the model response to land surface changes such as the Tibetan snow depth, a sensitivity study has also been conducted. For such sensitivity experiment, NIMBUS-7 SMMR snow depth data in spring are used as initial conditions in the RegCM3. Preliminary results indicate that RegCM3 is very much sensitive to Tibetan snow. The model simulated Indian summer monsoon circulation becomes weaker and the associated rainfall is reduced by about 30% with the introduction of 10 cm of snow over the Tibetan region in the month of April.     

Conditions leading to the onset of the Indian monsoon: A satellite perspective

Summary The summer monsoon onset-2004 over the Kerala Coast (Southern tip of the Indian Peninsula) was monitored in real-time using the Tropical Rainfall Measuring Mission (TRMM)/TMI derived total precipitable water vapor, wind speed and sea surface temperature (SST), National Centre for Environmental Prediction (NCEP) and QuikScat wind data. The 2004 onset was of a gradual type, with an early start (24 May), followed by slow growth to full strength (10 June). Hence, the unambiguous forecasting of such onsets becomes very difficult. The water vapor build up over the western Arabian Sea is one of the necessary conditions that gives us a lead time of two and half weeks for the onset of monsoon. The strength of the Hadley cell (monitored using NCEP meridional wind), which is associated with a large convective heat source is also used as a predictive parameter with a lead-time of two weeks. The other dynamical conditions considered are the early May propagation of the Madden Julian Oscillation (MJO) followed by a second MJO, which began in the Western Indian Ocean (WIO) and the kinetic energy over the South East Arabian Sea, with an early start around 24 May (50 m²/s²) and strengthening around 10 June (80 m²/s²). The setting of large-scale monsoon current using various satellite derived parameters and the distinct features for the year 2004 have been delineated.     

2014年8月西北太平洋和南海无TC生成之原因分析

利用常规气象观测资料、NCEP/NCAR 1°×1°的月平均再分析资料、NOAA卫星观测的OLR资料和中国气象局台风年鉴资料,对2014年8月西北太平洋和南海无TC生成的原因进行了诊断分析,结果表明：极地冷空气南侵,造成8月上中旬副热带高压偏东偏南,下旬冷空气减弱,副热带高压偏西偏南,致使副热带高压南侧偏东信风与赤道西风的汇合区位置异常偏南;马斯克林高压偏弱,导致索马里急流和东印度洋越赤道气流也弱,印度半岛中低层季风低压或季风槽极其不活跃。澳大利亚高压路径偏东或偏西和势力偏弱,则南海南部越赤道气流亦弱。8月上中旬台风主要源地的海表温度明显偏低,不能酿成低层高温高湿的大气;月内西北太平洋和南海大气的对流活动很弱,层结较稳定、风速垂直切变大,均不利于TC发生发展。在南海到菲律宾以东洋面低层为弱的正涡度区和负散度区,有辐合上升运动,但垂直速度很小,不能满足TC尺度的环流发生和发展;南亚高压和副高南侧东风扰动造成对流层高层为弱上升区,不能形成高空辐散机制,不利于上升气流维持和加强。故此,8月在异常偏南的ITCZ中生成的4个热带扰动最终均未能发展成台风。     

Prediction of summer monsoon rainfall over India using the NCEP climate forecast system

The performance of a dynamical seasonal forecast system is evaluated for the prediction of summer monsoon rainfall over the Indian region during June to September (JJAS). The evaluation is based on the National Centre for Environmental Prediction’s (NCEP) climate forecast system (CFS) initialized during March, April and May and integrated for a period of 9 months with a 15 ensemble members for 25 years period from 1981 to 2005. The CFS’s hindcast climatology during JJAS of March (lag-3), April (lag-2) and May (lag-1) initial conditions show mostly an identical pattern of rainfall similar to that of verification climatology with the rainfall maxima (one over the west-coast of India and the other over the head Bay of Bengal region) well simulated. The pattern correlation between verification and forecast climatology over the global tropics and Indian monsoon region (IMR) bounded by 50°E–110°E and 10°S–35°N shows significant correlation coefficient (CCs). The skill of simulation of broad scale monsoon circulation index (Webster and Yang; WY index) is quite good in the CFS with highly significant CC between the observed and predicted by the CFS from the March, April and May forecasts. High skill in forecasting El Nino event is also noted for the CFS March, April and May initial conditions, whereas, the skill of the simulation of Indian Ocean Dipole is poor and is basically due to the poor skill of prediction of sea surface temperature (SST) anomalies over the eastern equatorial Indian Ocean. Over the IMR the skill of monsoon rainfall forecast during JJAS as measured by the spatial Anomaly CC between forecast rainfall anomaly and the observed rainfall anomaly during 1991, 1994, 1997 and 1998 is high (almost of the order of 0.6), whereas, during the year 1982, 1984, 1985, 1987 and 1989 the ACC is only around 0.3. By using lower and upper tropospheric forecast winds during JJAS over the regions of significant CCs as predictors for the All India Summer Monsoon Rainfall (AISMR; only the land stations of India during JJAS), the predicted mean AISMR with March, April and May initial conditions is found to be well correlated with actual AISMR and is found to provide skillful prediction. Thus, the calibrated CFS forecast could be used as a better tool for the real time prediction of AISMR.     

南海夏季风强弱年环流形势与热带对流特点对比分析

利用NCEP/NCAR(美国国家环境预报中心/国家大气研究中心)再分析资料,对南海强夏季风年和弱夏季风年进行合成分析,结果表明,无论是在夏季风爆发前的1月份或是夏季风盛行的7月份,强弱夏季风年的平均经圈环流和平均纬圈环流都有明显差异。在强夏季风年,1月份的哈特莱环流、7月份的瓦克环流和季风经圈环流都比弱夏季风年同期的明显。强夏季风年的西太平洋副热带高压比弱夏季风年明显偏弱。利用OLR资料分析强夏季风年(1981年)和弱夏季风年(1983)4～9月份赤道东印度洋和南海对流活动的季节内振荡,发现在南海强夏季风年,季节内振荡的次数偏少而强度偏强,在弱夏季风年,季节内振荡的次数偏多而强度偏弱。相比之下,在南海强夏季风年,赤道东印度洋的季节内振荡比南海的更具典型性。     

关于南海夏季风建立的大尺度特征及其机制的讨论

使用1998年南海季风试验期间高质量资料和NCEP/NCAR40年再分析资料分析了南海季风建立前后的大尺度环流特征和要素的突变及爆发过程。发现南亚高压迅速地从菲律宾以东移到中南半岛北部,印缅槽加强,赤道印度洋西风加强并向东向北迅速扩展和传播,以及相伴随的中低纬相互作用和西太平洋副高连续东撤是南海夏季风建立的大尺度特征,与此同时,亚洲低纬地区的南北温差和纬向风切变也发生相应的突变。数值实验结果指出,印度半岛地形的陆面加热作用在其东侧激发的气旋性环流对于印缅槽的加强有重要作用,并进而有利于南海夏季风先于印度夏季风爆发。     

Characteristics of Zonal Propagation of Atmospheric Kinetic Energy at Equatorial Region in Asia

Based on the daily NCEP/NCAR reanalysis dataset from 1980 to 1997, the zonal propagations of 850 hPa kinetic energy (KE) and meridional wind (v) at equatorial region are examined respectively. Results show that the strongest center of KE in the tropical Asian monsoon region is located at 75°-90°E, with the secondary over the Somalia low-level jet channel, i.e., about 50°E. East to 90°E, disturbances of both KE and v observed are mainly coming from the western Pacific Ocean and propagating westward to the Bay of Bengal (BOB) passing through the South China Sea. But the propagation directions of both KE and v are rather disorderly between the BOB and the Somalia jet channel. Therefore, the East Asian summer monsoon and the Indian summer monsoon are different in the propagating features of the disturbances of KE and v. Above facts indicate that East Asian monsoon system exists undoubtedly even at the equatorial region, and quite distinct from the Indian monsoon system, it is mainly affected by the disturbances coming from the tropical western Pacific rather than from the Indian monsoon region. The boundary of the two monsoon systems is around 95°-100°E, which is more westward than the counterpart as proposed in earlier studies by 5-10 degrees in longitude.     

THE TEMPORAL AND SPATIAL CHARACTERISTICS OF MOISTURE BUDGETS OVER ASIAN AND AUSTRALIAN MONSOON REGIONS

Apparent moisture sink and water vapor transport flux are calculated by using NCAR/NCEP reanalyzed daily data for water vapor and wind fields at various levels from 1980 to 1989. With the aid of EOF analysis method, temporal and spatial characteristics of moisture budgets over Asian and Australian monsoon regions are studied. The results show that there is apparent seasonal transition of moisture sink and water vapor transport between Asian monsoon region and Australian monsoon region. In winter, the Asian monsoon region is a moisture source, in which three cross-equatorial water vapor transport channels in the "continent bridge". at 80°E and 40°E ～ 50°E transport water vapor to the Australian monsoon region and southern Indian Ocean which are moisture sinks. In summer, Australian monsoon region and southern Indian Ocean are moisture sources and by the three cross-equatorial transport channels water vapor is transport to the Asian monsoon region which is a moisture sink. In spring and autumn, ITCZ is the main moisture sink and there is no apparent water vapor transport between Asian monsoon region and Australian monsoon region.