Moisture Transport and Associated Background Circulation for the Regional Extreme Precipitation Events over South China in Recent 40 Years

Based on the hourly precipitation data at 176 observational stations over south China and the hourly ERA5reanalysis data during the 40-yr period of 1981-2020, we analyzed the universal characteristics of moisture transport and their associated background circulations for four types of regional extreme precipitation events(REPEs) over south China. Main findings are shown as follow.(i) The wind that transported moisture for the REPEs over south China featured a notable diurnal variation, which was consistent with the variations of the precipitation.(ii) Four types of REPEs could be determined, among which the southwest type(SWT) and the southeast type(SET) accounted for ~92%and ~5.7%, respectively, ranking the first and second, respectively.(iii) Trajectory analyses showed that the air particles of the SWT-REPEs had the largest specific humidity and experienced the most intense ascending motion, and therefore their precipitation was the strongest among the four types.(iv) South China was dominated by notable moisture flux convergence for the four types of REPEs, but their moisture transport was controlled by different flow paths.(v)Composite analyses indicated that the background circulation of the four types of REPEs showed different features,particularly for the intensity, location and coverage of a western Pacific subtropical high. For the SWT-REPEs, their moisture transport was mainly driven by a lower-tropospheric strong southwesterly wind band in the low-latitude regions. Air particles for this type of REPEs mainly passed over the Indochina Peninsula and South China Sea. For the SET-REPEs, their moisture transport was mainly steered by a strong low-tropospheric southeasterly wind northeast of a transversal trough. Air particles mainly passed over the South China Sea for this type of REPEs.

Seasonal Transition Features of Large-Scale Moisture Transport in the Asian-Australian Monsoon Region

Using NCEP/NCAR reanalysis data for the period of 1957-2001, the climatological seasonal transition features of large-scale vertically integrated moisture transport （VIMT） in the Asian-Australian monsoon region are investigated in this paper. The basic features of the seasonal transition of VIMT from winter to summer are the establishment of the summertime ＂great moisture river＂ pattern （named the GMR pattern） and its eastward expansion, associated with a series of climatological events which occurred in some ＂key periods＂, which include the occurrence of the notable southerly VIMT over the Indochina Peninsula in mid March, the activity of the low VIMT vortex around Sri Lanka in late April, and the onset of the South China Sea summer monsoon in mid May, among others. However, during the transition from summer to winter, the characteristics are mainly exhibited by the establishment of the easterly VIMT belt located in the tropical area, accompanied by some events occurring in ＂key periods＂. Further analyses disclose a great difference between the Indian and East Asian monsoon regions when viewed from the meridional migration of the westerly VIMT during the seasonal change process, according to which the Asian monsoon region can be easily divided into two parts along the western side of the Indochina Peninsula and it may also denote different formation mechanisms between the two regions.

The Impacts of Moisture Transport of East Asian Monsoon on Summer Precipitation in Northeast China

By using the ECMWF reanalysis daily data and daily precipitation data of 80 stations in Northeast China from 1961 to 2002, the impacts of moisture transport of East Asian summer monsoon on the summer precipitation anomaly in Northeast China, and the relationship between the variation of moisture budget and the establishment of East Asian summer monsoon in this region are studied. The results demonstrate that the moisture of summer precipitation in Northeast China mainly originates from subtropical, South China Sea, and South Asia monsoon areas. East China and its near coastal area are the convergent region of the monsoonal moisture currents and the transfer station for the currents continually moving northward. The monsoonal moisture transport, as an important link or bridge, connects the interaction between middle and low latitude systems. In summer half year, there is a moisture sink in Northeast China where the moisture influx is greater than outflux. The advance transport and accumulation of moisture are of special importance to pentad time scale summer precipitation. The onset, retreat, and intensity change of the monsoonal rainy season over Northeast China are mainly signified by the moisture input condition along the southern border of this area. The establishment of East Asian summer monsoon in this area ranges from about 10 July to 20 August and the onset in the west is earlier than that in the east. The latitude that the monsoon can reach is gradually northward from west to east, reaching 50°N within longitude 120°-135°E. In summer, the difference of air mass transport between summers with high and low rainfall mainly lies in whether more air masses originating from lower latitudes move northward through East China and its coastal areas, consequently transporting large amounts of hot and humid air into Northeast China.

Warm–dry collocation of recent drought in southwestern China tied to moisture transport and climate warming

This study aims to investigate the recent drought in southwestern China and its association with environmental changes in moisture transport （MT） and atmospheric circulation. Climatic Research Unit grid data, in situ observations in China, and ERA-interim reanalysis are used to study the characteristics of the drought and the associated mechanism. Recent precipitation trends show a pattern of ＂Northern wetting and Southern drying＂, similar to the anti-phase of the climate pattern prevailing during 1980--2000 in China's Mainland; southwestern China incurred a severe drought during 2009-20l 3. Wavelet analysis reveals that the drought coincides with a warm-dry phase of temperature and precipitation on a period of about 20 years and beyond 100 years, where contributions account for 43% and 57% of the deficiency of the precipitation, averaged for 2003-2012, respectively. A further investigation reveals that the drought results chiefly from the decline of the southwestern monsoon MT toward southwestern China, in addition to mid-latitude circulation changes, which leads to more blockings near the Ural Mountains and the Sea of Okhotsk in the rainy season and negative anomalies around Lake Baikal and northeast China in the dry season. These anomalies are likely to be correlated with global sea surface temperature changes and need to be studied further.

Impacts of Topographic Complexity on Modeling Moisture Transport and Precipitation over the Tibetan Plateau in Summer

The non-hydrostatic global variable resolution model(MPAS-atmosphere)is used to conduct the simulations for the South Asian Summer monsoon season(June,July,and August)in 2015 with a refinement over the Tibetan Plateau(TP)at the convection-permitting scale(4 km).Two experiments with different topographical datasets,complex(4-km)and smooth(60-km)topography,are designed to investigate the impacts of topographical complexity on moisture transport and precipitation.Compared with the observations and reanalysis data,the simulation can successfully capture the general features of key meteorological fields over the TP despite slightly underestimating the inflow through the southern TP.The results indicate that the complex topography can decrease the inward and outward moisture transport,ultimately increasing the total net moisture transport into the TP by~11%.The impacts of complex topography on precipitation are negligible over the TP,but the spatial distributions of precipitation over the Himalayas are significantly modulated.With the inclusion of complex topography,the sharper southern slopes of the Himalayas shift the lifted airflow and hence precipitation northward compared to the smooth topography.In addition,more small-scale valleys are resolved by the inclusion of complex topography,which serve as channels for moisture transport across the Himalayas,further favoring a northward shift of precipitation.Overall,the difference between the two experiments with different topography datasets is mainly attributed to their differing representation of the degree of the southern slopes of the Himalayas and the extent to which the valleys are resolved.

NUMERICAL SIMULATION OF THE RELATIONSHIP BETWEEN THE MAINTENANCE AND INCREASE IN HEAVY RAINFALL OF THE LANDING TROPICAL STORM BILIS AND MOISTURE TRANSPORT FROM LOWER LATITUDES

The NCEP/NCAR reanalysis, Japan Meteorological Agency(JMA) tropical cyclone tracks and intensive surface observations are used to diagnose the features of moisture transport of tropical storm Bilis(No. 0604), which is simulated by the WRF(weather research and forecasting) mesoscale numerical model. It is shown that the Bilis was linked with the moisture channel in the lower latitudes after its landing. Meanwhile, the cross-equatorial flows over 80°-100°E and Somali were active and brought abundant water vapor into the tropical storm, facilitating the maintenance of the landing storm with intensified heavy rainfall along its path. The simulation suggested that the decreased water vapor from lower latitudes prevents the maintenance of Bilis and the development of rainfall. While the cross-equatorial flows over 80°-100°E and Somali were in favor of keeping the cyclonic circulation over land. If the moisture supply fro m the Somali jet stream was reduced, the strength and area of heavy rainfall in tropical cyclone would be remarkably weakened. Consequently, the decreased water vapor from lower latitudes can remarkably suppress the deep convection in tropical storm, then Bilis was damped without the persistent energy support and the rainfall was diminished accordingly.

A decomposition study of moisture transport divergence for inter-decadal change in East Asia summer rainfall during 1958-2001

In this paper, we report on the results of an investigation into inter-decadal changes in moisture transport and divergence in East Asia for the two periods 1980-2001 and 1958 1979. The aim is to explore the mechanism of summer rainfall change in the region after abrupt changes. The relevant changes are calculated using ERA-40 daily reanalysis datasets. The results show that both stationary and transient eddy moisture transports to the Chinese mainland have declined since the abrupt change in atmospheric general circulation in the late 1970s, leading to more rainfall in South China and less in the North. The anomalous rainfall pattern coincides well with anomalous large-scale moisture divergence in the troposphere, of which stationary-wave or monsoon transport is dominant, in comparison with the contribution of the transient eddies. F^rthermore, their divergences are found to be in opposite phases. In addition, meridional divergence is more important than its zonal counterpart, with an opposite phase in East Asia. Abnormal zonal moisture convergences appear in northwestern and northeastern parts of China, and are related to the excess rainfalls in these regions. An increase in transient eddy activity is one of the major mechanisms for excess rainfall in northern Xinjiang. Consequently, the anomalous rainfall pattern in East Asia results from a decline of the East Asian monsoon after the abrupt change, while the rainfall increase in northwestern China involves anomalies of both stationary waves and transient eddies on boreal westerly over the mid- and high latitudes.

Pathways of meridional atmospheric moisture transport in the central Arctic

Atmospheric moisture transport plays an important role in latent heat release and hydrologic interactions in the Arctic.In recent years,with the rapid decline in sea ice,this transport has changed.Here,we calculated the vertically integrated atmospheric moisture meridional transport(AMTv)from two global reanalysis datasets,from1979–2015,and found moisture pathways into the central Arctic.Four stable pathways showed an occurrence frequency greater than 70%,and these pathways exhibited a perennial seasonal pattern in the atmosphere above the Laptev Sea Pathway(LSP),Canadian Arctic Archipelago Pathway(CAAP),both sides of the Greenland plateau.Another seasonal pathway appeared above the east of the Chukchi Sea(CSP)during the melting/freezing months(March to September).Through these pathways,AMTv contributed a total moisture exchange of60%–80%—averaged over a 75°N circle—and focused on the low troposphere.Transports across the LSP,CSP and CAAP pathways likely create an enclosed moisture route.Meridional moisture fluxes are intensified in the Pacific sector of Arctic(PSA),especially during melting/freezing months.AMTv interannual variabilities are illustrated mainly in the Laptev Sea and the east Greenland pathway.Results indicate that accompanying a tendency for a stronger Beaufort Sea High in this sea level pressure field,AMTv through PSA pathways,switched from output to input,and approximately 960 km^3 of equivalent liquid water was transferred into the central Arctic during each decade.The detrended AMTv increment is highly correlated with the rapid decline of old ice areas(correlation coefficient is–0.78)for their synchronous fluctuations in the 1980 s and the last decade.

Role of Extratropical Cyclones in the Recently Observed Increase in Poleward Moisture Transport into the Arctic Ocean

Poleward atmospheric moisture transport(AMT) into the Arctic Ocean can change atmospheric moisture or water vapor content and cause cloud formation and redistribution, which may change downward longwave radiation and, in turn, surface energy budgets, air temperatures, and sea-ice production and melt. In this study, we found a consistently enhanced poleward AMT across 60?N since 1959 based on the NCAR–NCEP reanalysis. Regional analysis demonstrates that the poleward AMT predominantly occurs over the North Atlantic and North Pacific regions, contributing about 57% and 32%, respectively, to the total transport. To improve our understanding of the driving force for this enhanced poleward AMT, we explored the role that extratropical cyclone activity may play. Climatologically, about 207 extratropical cyclones move across 60?N into the Arctic Ocean each year, among which about 66(32% of the total) and 47(23%) originate from the North Atlantic and North Pacific Ocean, respectively. When analyzing the linear trends of the time series constructed by using a 20-year running window, we found a positive correlation of 0.70 between poleward yearly AMT and the integrated cyclone activity index(measurement of cyclone intensity, number, and duration). This shows the consistent multidecadal changes between these two parameters and may suggest cyclone activity plays a driving role in the enhanced poleward AMT. Furthermore, a composite analysis indicates that intensification and poleward extension of the Icelandic low and accompanying strengthened cyclone activity play an important role in enhancing poleward AMT over the North Atlantic region.

Numerical Simulation on Moisture Transport in Cracked Cement-based Materials in view of Self-healing of Crack

The moisture transport in cracked cement-based materials was investigated with priority by numerical simulation.The cracked cement-basis material was treated as two components system,including the cracks and cementitious mortar.The mass balance between the water in the cracks and in the cement mortar was considered.From the modeling results,it was seen that the water or vapor filled the crack immediately when the cracked cementitious mortar was put into contact with the water or vapor.The water/vapor penetrates into the mortar from the crack surfaces,as well as the external surface exposed in the outside condition.The existence of cracks increases the penetration of water/vapor into the cementitious mortar.As the basis for studying the self-healing in cracked concrete,the simulation on moisture transport provided important information about the water distribution and movement inside the cracked concrete.

Quantifying the Spatial Characteristics of the Moisture Transport Affecting Precipitation Seasonality and Recycling Variability in Central Asia

Moisture contribution and transport pathways for Central Asia(CA)are quantitatively examined using the Lagrangian water cycle model based on reanalysis and observational data to explain the precipitation seasonality and the moisture transport variation during 1979-2015.Westerly-related(northwesterly and westerly)transport explains 42%of CA precipitation and dominates in southwest CA,where precipitation is greatest in the cold season.Southeast CA,including part of Northwest China,experiences its maximum precipitation in the warm season and is solely dominated by southerly transport,which explains about 48%of CA precipitation.The remaining 10%of CA precipitation is explained by northerly transport,which steadily impacts north CA and causes a maximum in precipitation in the warm season.Most CA areas are exposed to seasonally varying moisture transport,except for southeast and north CA,which are impacted by southerly and northerly transport year-round.In general,the midlatitude westerlies-driven transport and the Indian monsoon-driven southerly-related transport explain most of the spatial differences in precipitation seasonality over CA.Moreover,the contribution ratio of local evaporation in CA to precipitation exhibits significant interdecadal variability and a meridionally oriented tripole of moisture transport anomalies.Since the early 2000s,CA has experienced a decade of anomalously low local moisture contribution,which seems jointly determined by the weakened moisture contribution from midlatitudes(the Atlantic,Europe,and CA itself)and the enhanced contribution from high latitudes(West Siberia and the Arctic)and tropical areas(South Asia and the Indian Ocean).

Research in Moisture Transport through One and Two-layered Porous Composites

Research into the moisture transport processes in porous materials is primarily important for theoretical modelling and industrial applications in the design of energy saving buildings and living environments, etc. Based on experimental investigation, we propose new models which describe one-dimensional transport through one-layered uniform materials and dissimilar two-layered composites. Diffusivity as a function of moisture content is obtained through a Boltzman transformation, master curves, and combined numerical and regression techniques. Transport processes in one and two-layered composites are simulated on the basis of extended unsaturated Darcy’s Law using the finite element method (FEM). Simulation results show significantly different transport patterns of moisture profile when moisture migrates in different directions, and high agreement with experimental moisture profiles. Keywords Porous materials - moisture transport - two-layered composites - modelling and simulation Qingguo Wang graduated from Hebei Normal University, China, in 1985. He received the M.Sc. degree from Beijing Petroleum University in 1988 and the Ph.D. degree from the University of Luton, UK, in 2005. He is currently a Research Associate in the Department of Electrical Engineering and Electronics at the University of Liverpool, UK and an Associate Professor of Shijiazhuang Mechanical Engineering College, China. His research interests include measurement and control, mass and heat transportation, EMC, etc.Kemal Ahmet graduated in physics from the University of Leeds. Following the completion of his masters degree, he completed his Ph.D. at the University of London in the area of nuclear instrumentation in 1992. Until recently, he was a Principal Lecturer at the University of Luton, leading a research group in moisture instrumentation, measurement and monitoring. In 2004 he joined Medtronic, world leader in medical technology, and is currently working in the Neurologic Technologies division as a specialist in powered surgical instrumentation.Young Yue is a Principal Lecturer at the University of Luton, UK. He holds a B.Sc. in mechanical engineering from the Northeastern University, China, and a Ph.D. from Heriot-Watt University, UK. He is a chartered engineer and a member of the Institution of Mechanical Engineers, UK. Dr. Yue has been working in academia for 15 years following his 8 years of industrial experience. His main research interests are CAD/CAM, geometric modelling, virtual reality, and pattern recognition. He has over 70 publications in refereed books, journals and conferences.

The Key Supply Source of Long-Distance Moisture Transport for the Extreme Rainfall Event on July 21, 2012 in Beijing

In this study,the Weather Research and Forecasting(WRF)model and meteorological observation data were used to research the long-distance moisture transport supply source of the extreme rainfall event that occurred on July 21,2012 in Beijing.Recording a maximum rainfall amount of 460 mm in 24 h,this rainstorm event had two dominant moisture transport channels.In the early stage of the rainstorm,the first channel comprised southwesterly monsoonal moisture from the Bay of Bengal(BOB)that was directly transported to north China along the eastern edge of Tibetan Plateau(TP)by orographic uplift.During the rainstorm,the southwesterly moisture transport was weakened by the transfer of Typhoon Vicente.Moreover,the southeasterly moisture transport between the typhoon and western Pacific subtropical high(WPSH)became another dominant moisture transport channel.The moisture in the lower troposphere was mainly associated with the southeasterly moisture transport from the South China Sea and the East China Sea,and the moisture in the middle troposphere was mainly transported from the BOB and Indian Ocean.The control experiment well reproduced the distribution and intensity of rainfall and moisture transport.By comparing the control and three sensitivity experiments,we found that the moisture transported from Typhoon Vicente and a tropical cyclone in the BOB both significantly affected this extreme rainfall event.After Typhoon Vicente was removed in a sensitivity experiment,the maximum 24-h accumulated rainfall in north China was reduced by approximately 50%compared with that of the control experiment,while the rainfall after removing the tropical cyclone was reduced by 30%.When both the typhoon and tropical cyclone were removed,the southwesterly moisture transport was enhanced.Moreover,the sensitivity experiment of removing Typhoon Vicente also weakened the tropical cyclone in the BOB.Thus,the moisture pump driven by Typhoon Vicente played an important role in maintaining and strengthening the tropical cyclone in the BOB through its westerly airflow.Typhoon Vicente was not only the moisture transfer source for the southwesterly monsoonal moisture but also affected the tropical cyclone in the BOB,which was a key supply source of long-distance moisture transport for the extreme rainfall event on July21,2012 in Beijing.

Anomalies of Precipitation over China on Days with Tropical Cyclone Activity over the Bay of Bengal: Role of Moisture Transport

Tropical cyclones over the Bay of Bengal(BoBTC)affect the precipitation over China,with distinct seasonal and daily variabilities.This study quantitatively examines the daily standardized precipitation anomalies(SPAs)over China on the days with BoBTC activities(storm-days)and related circulations,based on rainfall measurements at surface meteorological stations and ECMWF reanalysis data on a 0.25°×0.25°resolution during 1979-2019.Significant positive SPA is found over the stations in the two adjacent regions around BoB(Southwest China in May/November and southern Tibetan Plateau in October)and three distant regions(Southeast China and the northeastern boundary of the Qinghai-Tibet Plateau in May,and central North China in October).The SPA distributions are remarkably consistent with the integrated water vapor transport(IVT)anomalies.Enhanced IVT is found associated with the interaction between southwesterly(southerly)of the BoBTC circulation and low-level monsoonal flow in May(midlevel westerly in winter months).The probabilities of extreme precipitation(EP)occurrences over the above regions all increase on storm-days.For adjacent regions,EP is significantly correlated with the northward IVT anomalies to the east of BoBTC circulation,which strengthen the water vapor input through the southern border.Such IVT anomalies are stronger in May,benefited by the deep monsoonal southwesterlies than those in November.For distant regions,EP is more closely related to the IVT anomaly extending back from BoB.Enhanced moisture from BoB concentrates along a local low-level convergence line over Southeast China,being further facilitated by coexistence of the BoBTC depression and midlevel westerly trough in midlatitudes.Our results highlight the interactions between BoBTCs and local weather systems that influence the general precipitation anomalies and occurrence of EP over China,especially over distant regions.

Moisture Transport in the Asian Summer Monsoon Region and Its Relationship with Summer Precipitation in China

The characteristics of moisture transport over the Asian summer monsoon region and its relationship with summer precipitation in China are examined by a variety of statistical methods using the NCEP/NC AR reanalysis data for 1948-2005.The results show that：1） The zonal-mean moisture transport in the Asian monsoon region is unique because of monsoon activities.The Asian summer monsoon region is a dominant moisture sink during summer.Both the Indian and East Asian monsoon areas have their convergence center, respectively.2） Most moisture congregates in the lower troposphere primarily from the Bay of Bengal in the mid and upper layers,and the vapor flux comes from mid-latitude westerlies as well as the tropical western Pacific Ocean.3） The moisture fluxes by the Indian monsoon enhance from May to July mostly in the zonal transport while those by the East Asian monsoon intensify mainly in the meridional transport from June to July.Both reach their maxima in July and then decrease from August.The sub-tropical westerly moisture fluxes south to the Tibetan Plateau across 90°E are strong in spring,while the mid-high latitude and tropical westerly vapor transfers change in phase and increase from January to July.The tropical westerly transport accounts for about 80%of the total moisture transport in July and only 18%from mid-high latitudes. 4） The moisture transfer and budgets over the Asian monsoon region undergo a substantial change after the South China Sea monsoon onset,especially over the Bay of Bengal,Indo-China Peninsula,and South China Sea.The northern boundary of the South China Sea is of great importance in providing abundant moisture for China mainland during summer.5） The northward progress of the moisture transfer coincides with the seasonal march of the monsoon rainbelts very well.EOF1 of the moisture transport field basically depicts the consistent northward transport anomaly with an obvious decreasing trend over the East Asian monsoon region from 1951 to 2005.Further analyses suggest that this trend owing to the weakening of the East Asian summer monsoon is largely responsible for the decline of rainfall over North China.The EOF2 reveals that moisture flux convergence from northeast and southwest over the Yangtze River valley shows a slight increasing tendency from the 1980s and it is consistent with the fact of more frequently occurred heavy rainfall over there.The correlation analyses indicate that the interdecadal variation of the East Asian summer monsoon accounts for the main part of the variation.

Moisture Origins and Transport Processes for the 2020 Yangtze River Valley Record-Breaking Mei-yu Rainfall

The summer of 2020 recorded a record-breaking flood due to excessive mei-yu rain falling over the Yangtze River Valley(YRV).Using the Lagrangian model FLEXPART,this paper investigates moisture sources and transport processes behind this extreme event.Based on climate data from 1979 to 2019,the air-particle(an infinitesimally small air parcel)trajectories reaching the YRV show sectors that correspond to five main moisture sources:the Indian monsoon region(IND,27.5%of the total rainfall),the local evaporation(27.4%),the Western Pacific Ocean(WPO,21.3%),the Eurasian continent(8.5%)and Northeast Asia(4.4%).In the 2020 mei-yu season,moisture from all source regions was above normal except that from Northeast Asia.A record-breaking moisture source from the IND and WPO dominated this extreme mei-yu flood in 2020,which was 1.5 and 1.6 times greater than the climate mean,respectively.This study reveals a significant relationship between the moisture source with three moisture transport processes,i.e.,trajectory density,moisture content,and moisture uptake of air-particles.A broad anomalous anticyclonic circulation over the Indo-Northwestern Pacific(Indo-NWP)provides a favorable environment to enhance the moisture transport from the IND and WPO into the YRV.In the 2020 mei-yu season,a record-breaking Indo-NWP anomalous anticyclonic circulation contributed to a higher trajectory density as well as higher moisture content and moisture uptake of air-particles from the IND and WPO regions.This collectively resulted in unprecedented moisture transport from source origins,thus contributing to the mei-yu flood over the YRV in 2020.

The Response of Anomalous Vertically Integrated Moisture Flux Patterns Related to Drought and Flood in Southern China to Sea Surface Temperature Anomaly

With the extreme drought(flood)event in southern China from July to August in 2022(1999)as the research object,based on the comprehensive diagnosis and composite analysis on the anomalous drought and flood years from July to August in 1961-2022,it is found that there are significant differences in the characteristics of the vertically integrated moisture flux(VIMF)anomaly circulation pattern and the VIMF convergence(VIMFC)anomaly in southern China in drought and flood years,and the VIMFC,a physical quantity,can be regarded as an indicative physical factor for the"strong signal"of drought and flood in southern China.Specifically,in drought years,the VIMF anomaly in southern China is an anticyclonic circulation pattern and the divergence characteristics of the VIMFC are prominent,while those are opposite in flood years.Based on the SST anomaly in the typical draught year of 2022 in southern China and the SST deviation distribution characteristics of abnormal draught and flood years from 1961 to 2022,five SST high impact areas(i.e.,the North Pacific Ocean,Northwest Pacific Ocean,Southwest Pacific Ocean,Indian Ocean,and East Pacific Ocean)are selected via the correlation analysis of VIMFC and the global SST in the preceding months(May and June)and in the study period(July and August)in 1961-2022,and their contributions to drought and flood in southern China are quantified.Our study reveals not only the persistent anomalous variation of SST in the Pacific and the Indian Ocean but also its impact on the pattern of moisture transport.Furthermore,it can be discovered from the positive and negative phase fitting of SST that the SST composite flow field in high impact areas can exhibit two types of anomalous moisture transport structures that are opposite to each other,namely an anticyclonic(cyclonic)circulation pattern anomaly in southern China and the coastal areas of east China.These two types of opposite anomalous moisture transport structures can not only drive the formation of drought(flood)in southern China but also exert its influence on the persistent development of the extreme weather.

ROLE IN MOISTURE TRANSPORTATION OF SEASONAL MEAN AND INTRASEASONAL OSCILLATIONS IN ASIAN SUMMER MONSOON AREA——LONG-TERM AVERAGE CHARACTERISTICS

By use of the May—September 1980—1986 ECMWF daily data of u,v,r and T at 850 hPa,a comparative analysis is performed of basic features of moisture transportation at seasonal mean,quasi-40-day,-biweekly,and-weekly oscillations,indicating that the seasonal mean transfer plays a decisive role in the moisture flux over the Asian monsoon region,displaying the integer of the monsoon systems there in character;that the transport related to these tropical intraseasonal oscillations are of equal importance in the monsoon period except the difference in their behaviors,i.e.,the transfer shows considerable relative independence in the South-and East-Asian systems;and that the transport at all these intraseasonal oscillations is found to be feeble at equatorial latitudes with little or no influence on each other for both hemispheres.

A Study on Water Vapor Transport and Budget of Heavy Rain in Northeast China

The characteristics of moisture transport and budget of widespread heavy rain and local heavy rain events in Northeast China are studied using the NCEP-NCAR reanalysis 6-hourly and daily data and daily precipitation data of 200 stations in Northeast China from 1961-2005. The results demonstrate that during periods with widespread heavy rain in Northeast China, the Asian monsoon is very active and the monsoonal northward moisture transport is strengthened significantly. The widespread heavy rainfall obtains enhanced water vapor supply from large regions where the water vapor mainly originates from the Asian monsoon areas, which include the East Asian subtropical monsoon area, the South China Sea, and the southeast and southwest tropical monsoon regions. There are several branches of monsoonal moisture current converging on East China and its coastal areas, where they are strengthened and then continue northward into Northeast China. Thus, the enhanced northward monsoonal moisture transport is the key to the widespread heavy rain in Northeast China. In contrast, local heavy rainfall in Northeast China derives water vapor from limited areas, transported by the westerlies. Local evaporation also plays an important role in the water vapor supply and local recycling process of moisture. In short, the widespread heavy rains of Northeast China are mainly caused by water vapor advection brought by the Asian monsoon, whereas local heavy rainfall is mainly caused by the convergence of the westerly wind field.

Climatological Characteristics of the Moisture Budget and Their Anomalies over the Joining Area of Asia and the Indian-Pacific Ocean

The climatological characteristics of the moisture budget over the joining area of Asia and the IndianPacific Ocean （AIPO） and its adjacent regions as well as their anomalies have been estimated in this study. The main results are as follows. In the winter, the northeasterly moisture transport covers the extensive areas at the lower latitudes of the AIPO. The westerly and northerly moisture transport is the major source and the South Indian Ocean （SIO） is the moisture sink. In the summer, influenced by the southwesterly monsoonal wind, the crossequatorial southwesterly moisture transport across Somali originating from the SIO is transported through the Arabian Sea （AS）, the Bay of Bengal （BOB）, and the South China Sea （SCS） to eastern China. The AIPO is controlled by the southwesterly moisture transport. The net moisture influx over the AIPO has obvious interannual and interdecadal variations. From the mid- or late 1970s, the influxes over the SIO, the AS, the northern part of the western North Pacific （NWNP）, and North China （NC） as well as South China （SC） begin to decrease abruptly, while those over Northeast China （NEC） and the Yangtze River-Huaihe River basins （YHRB） have increased remarkably. As a whole, the net moisture influxes over the BOB and the southern part of the western North Pacific （SWNP） in the recent 50 years take on a linear increasing trend. However, the transition timing for these two regions is different with the former being at the mid- or late 1980s and the latter occurring earlier, approximately at the early stage of the 1970s. The anomalous moisture source associated with the precipitation anomalies is different from the normal conditions of the summer precipitation. For the drought or flood years or the years of E1 Nifio and its following years, the anomalous moisture transport originating from the western North Pacific （WNP） is the vital source of the anomalous precipitation over eastern China, which is greatly related with the variation of the subtropical Pacific high.