Relations of Water Vapor Transport from Indian Monsoon with That over East Asia and the Summer Rainfall in China

A diagnostic study is made to investigate the relationship between water vapor transport from Indian monsoon and that over East Asia in Northern summer. It is found that water vapor transport from Indian monsoon is inverse to that over East Asia. More (less) Indian monsoon water vapor transport corresponds to less (more) water vapor transport over East Asia and less (more) rainfall in the middle and lower reaches of the Yangtze River valley. The Indian summer monsoon water vapor transport is closely related to the intensity of the western Pacific subtropical high in its southwestern part. The stronger (weaker) the Indian summer monsoon water vapor transport, the weaker (stronger) the western Pacific subtropical high in its southwestern part, which leads to less (more) water vapor transport to East Asia, and thus less (more) rainfall in the middle and lower reaches of the Yangtze River valley. Analysis of the out-going longwave radiation anomalies suggests that the convective heating anomalies over the Indian Ocean may have significant impact not only on the Indian monsoon, but also on the East Asian monsoon.

The Recent Interdecadal and Interannual Variation of Water Vapor Transport over Eastern China

The climatological characteristics and interdecadal variability of the water vapor transport and budget over the Yellow River-Huaihe River valleys （YH1） and the Yangtze River-Huaihe River valleys （YH2） of East China were investigated in this study,using the NCEP/NCAR monthly mean reanalysis datasets from 1979 to 2009.Changes in the water vapor transport pattern occurred during the late 1990s over YH1 （YH2） that corresponded with the recent interdecadal changes in the eastern China summer precipitation pattern.The net moisture influx in the YH1 increased and the net moisture influx in the YH2 decreased during 2000-2009 in comparison to 1979-1999.Detailed features in the moisture flux and transport changes across the four boundaries were explored.The altered water vapor transport over the two domains can be principally attributed to the additive effects of the changes in the confluent southwesterly moisture flow by the Indian summer monsoon and East Asian summer monsoon （related with the eastward recession of the western Pacific subtropical high）.The altered water vapor transport over YH1 was also partly caused by the weakened midlatitude westerlies.

Interannual and Interdecadal Variability of Atmospheric Water Vapor Transport in the Haihe River Basin

The seasonal mean atmospheric precipitable water and water vapor transport over the Haihe River Basin （HRB） in North China with a focus on their interannual to interdecadal variability, and then the relationships of the interannual and interdecadal variability of the water cycle over the HRB to the Pacific Decadal Oscillation （PDO） and E1 Nino-Southern Oscillation （ENSO） phenomena were investigated using the observational and National Centers for Environmental Prediction （NCEP） reanalysis data. There was a strong interdecadal variability for the water cycle （such as precipitation and water vapor transport） over the region, with an abrupt change occurring mostly in the mid 1970s. The intensity of the East Asian summer monsoon largely affected the atmospheric water vapor transport. Generally, the net meridional convergence of the water vapor flux over the region was relatively large before 1965, and it declined gradually from then on with a further notable decrease since mid 1970s. Zonal water vapor transport was similar to meridional, but with a much smaller magnitude and no noteworthy turning in the mid 1970s. Results also suggested that the wind field played an important role in the water vapor transport over the HRB before the mid 1960s, and the interdecadal variability of the water cycle （precipitation, water vapor transport, etc.） in the summer was related to the PDO; however, interannual variation of the water vapor transport could also be related to the ENSO phenomena.

Water Vapor Transport and Cross-Equatorial Flow over the Asian-Australia Monsoon Region Simulated by CMIP5 Climate Models

The summer mean water vapor transport （WVT） and cross-equatorial flow （CEF） over the Asian- Australian monsoon region simulated by 22 coupled atmospheric-oceanic general circulation models （AOGCMs） from the World Climate Research Programme＇s Coupled Model Intercomparison Project Phase 5 （CMIP5） were evaluated. Based on climatology of the twentieth-century simulations, most of models have a reason- ably realistic representation of summer monsoon WVT characterized by southeast water vapor conveyor belt over the South Indian Ocean and southwest belt from the Arabian Sea to the East Asian. The correlation coefficients between NCEP reanalysis and simulations of BCC-CSMI-1, BNU-ESM, CanESM2, FGOALS-s2, MIROC4h and MPI-ESM-LR are up to 0.8. The simulated CEF depicted by the meridional wind along the equator includes the Somali jet and eastern CEF in low atmosphere and the reverse circulation in upper atmosphere, which were generally consistent with NCEP reanalysis. Multi-model ensemble means （MME） can reproduce more reasonable climatological features in spatial distribution both of WVT and CEF. Ten models with more reasonable WVT simulations were selected for future projection studies, including BCC- CSMI-1, BNU-ESM, CanESM2, CCSM4, FGOALS-s2, FIO-ESM, GFDL-ESM2G, MRIOCS, MPI-ESM-LR and NorESM-1M. Analysis based on the future projection experiments in RCP （Representative Concentra- tion Pathway） 2.6, RCP4.5, RCP6 and RCP8.5 show that the global warming forced by different RCP scenarios will results in enhanced WVT over the Indian area and the west Pacific and weaken WVT in the low latitudes of tropical Indian Ocean.

Characteristics of the Mean Water Vapor Transport over Monsoon Asia

Based on ECMWF monthly mean data from January 1980 to December 1989,characterishcs of the three-dimensional structure of the mean water vapor transport over Monsoon Asia are described,and the more forportant features of the different regional water vapor transport in the indian Monsoon region and the East AsianMonsoon region are analyzed.It is found that there is a moist tongue extending from the equator POleWard to the Asian Monsoon region.The three-dimensional distributions of the mean water vapor transport fields over the entire globe renect clearly the asymmetry of the Asian Monsoon system,and the existence of a counterrHadley monsoon circulation.The moisture conver-gened(divergence) area in Asia coincides with the connuellt(diffiuent) zone of the monsoon cjrculahon.Furthermore,the moist featllres of the tWo sub-regions of the Asian Monsoon area are different both in their magnitudes and in their seasonal variations.

Interdecadal Variability of Spring Precipitation over South China and Its Associated Atmospheric Water Vapor Transport

The characteristics of spring precipitation and water vapor transport in South China were analyzed by using observational data and the National Centers for Environmental Prediction (NCEP) reanalysis data. The results show that, during the spring, each component of the water cycle (precipitation, wind field, specific humidity, water vapor transport, etc.) in South China exhibits a notable interdecadal variability. An abrupt increase in spring precipitation occurred in the early 1970s. During the dry period from 1958 to 1971, a water vapor flux divergence (positive divQ) existed in South China, which may have led to the deficiency in rainfall. However, during the wet period from 1973 to 1989, there was a remarkable water vapor flux convergence (negative divQ) in South China, which may have resulted in the higher rainfall. The interdecadal variability of water vapor transport is closely related to the interdecadal variability of wind fields, although the interdecadal variability of specific humidity also plays a role to some extent, and the interdecadal variability of the zonal water vapor transport contributes much more to the interdecadal variability of spring precipitation than the meridional water vapor transport.

Water vapor transport over China and its relationship with drought and flood in Yangtze River Basin

The characteristics of water vapor transport(WVT) over China and its relationship with precipitation anomalies in the Yangtze River Basin(YRB) are analyzed by using the upper-air station data in China and ECMWF reanalysis data in summer from 1981 to 2002.The results indicate that the first mode of the vertically integrated WVT is significant whose spatial distribution presents water vapor convergence or divergence in the YRB.When the Western Pacific Subtropical High(WPSH) is strong and shifts southward and westward, the Indian Monsoon Low Pressure(IMLP) is weak, and the northern part of China stands behind the middle and high latitude trough, a large amount of water vapor from the Bay of Bengal(BOB), the South China Sea(SCS) and the western Pacific forms a strong and steady southwest WVT band and meets the strong cold water vapor from northern China in the YRB, thus it is likely to cause flood in the YRB.When WPSH is weak and shifts northward and eastward, IMLP is strong, and there is nearly straight west wind over the middle and high latitude, it is unfavorable for oceanic vapor extending to China and no steady and strong southwest WVT exists in the region south of the YRB.Meanwhile, the cold air from northern China is weak and can hardly be transported to the YRB.This brings on no obvious water vapor convergence, and then less precipitation in the YRB.

Projected changes in summer water vapor transport over East Asia under the 1.5°C and 2.0°C global warming targets

This study investigates changes in summer water vapor transport(WVT) over East Asia under 1.5°C and 2.0°C global warming(GW) for the +4.5 and +8.5 W m-2 Representative Concentration Pathway(RCP) scenarios(RCP4.5 and RCP8.5, respectively). Of the 27 models used, 18 show better skill in simulating the climatological summer WVT over East Asia of the present day. Of those 18, 13 reach 1.5°C and 2.0°C GW for the two RCPs. Based on these 13 models, results show that — relative to the present day-th e summer WVT is enhanced over East Asia under 1.5°C and 2.0°C GW for RCP4.5 and RCP8.5. The inte r-model consistency is higher under 2.0°C GW. Increased water vapor content favors the enhanced WVT over both southern and northern East Asia, while lower-level circulation contributes to the enhanced WVT over southern East Asia. Compared to 1.5°C GW, th e summer WVT under 2.0°C GW is further enhanced over most of East Asia for RCP4.5. For RCP8.5, the summer WVT is also further enhanced over southern East Asia, while this is not the case over northern East Asia. Under the additional 0.5°C GW, the changes in summer WVT, with low in ter-model consistency, are closely related to anomalous lower-level circulation. Precipitation increases over the East China Sea to southern Japan, the Korean Peninsula, and North China, for both RCP4.5 and RCP8.5. However, the changes in precipitation over the South China Sea and Northeast China are different for the two RCPs. This is connected to the difference in the changes of WVT divergence.

Characteristics of the Correlation between Regional Water Vapor Transport along with the Convective Action and Variation of the Pacific Subtropical High in 1998

This paper explores the impact of the convective action over the low-latitude region, the water vapor transport around the West Pacific subtropical high (WPSH), and its convective action on the seasonal northward jump and southward withdrawal of the WPSH in summer by using the daily data set of NCEP and TBB for 1998. The research shows that in summer, the WPSH moves northward when the convection over the low-latitude tropical region intensifies and the subsidence region of the meridional vertically vertical circulation in meridional direction circulation over the region of 110?150癊 moves northward. Furthermore, as revealed by diagnostic analysis, the subtropical high moves northward after the obvious weakening of the longitudinal water vapor transport over the region around the subtropical high, but withdraws southward a pentad after the reduction of the latitudinal water vapor transport over the tropical West Pacific region. The research results show that the northward jump and southward withdrawal of the WPSH are closely related to the release of the convective latent heat at low latitudes and the water vapor transport at boundaries around WPSH and its convective action. The numerical simulation further validates the above-mentioned correlation between the variation of the action of the subtropical high and the preceding water vapor transport along with the convection characteristics.

Inversion of Evaporation and Water Vapor Transport Using HY-2 Multi-Sensor Data

HY-2 satellite is the first marine dynamic environment satellite of China.In this study,global evaporation and water vapor transport of the global sea surface are calculated on the basis of HY-2 multi-sensor data from April 1 to 30,2014.The algorithm of evaporation and water vapor transport is discussed in detail,and results are compared with other reanalysis data.The sea surface temperature of HY-2 is in good agreement with the ARGO buoy data.Two clusters are shown in the scatter plot of HY-2 and OAFlux evaporation due to the uneven global distribution of evaporation.To improve the calculation accuracy,we compared the different parameterization schemes and adopted the method of calibrating HY-2 precipitation data by SSM/I and Global Precipitation Climatology Project(GPCP)data.In calculating the water vapor transport,the adjustment scheme is proposed to match the balance of the water cycle for data in the low latitudes.

LONG-DISTANCE-RELAYED WATER VAPOR TRANSPORT EAST OF TIBETAN PLATEAU AND ITS IMPACTS

This paper attempts to reveal a long-distance-relayed water vapor transport(LRWVT) east of Tibetan Plateau and its impacts. The results show that from August to October, east of Tibetan Plateau, there exists a unique LRWVT,and the water vapor from the South China Sea and the western Pacific can affect the Sichuan Basin, Northwest China and other Chinese regions far from the tropical sea through this way. From August to October, the precipitation of the region east of the Plateau is closely linked both in the intra-annual and inter-annual variations, and the LRWVT from the South China Sea and the western Pacific is an important connection mechanism. The large-scale circulation background of the LRWVT impacting the precipitation of the region east of the Plateau is as follows: At high levels,the South Asian High is generally stronger than normal and significantly enhances with its northward advance and eastward extension over the region east of the Plateau. At mid-level, a broad low pressure trough is over Lake Balkhash and its surroundings, and the Western Pacific Subtropical High(WPSH) is northward and westward located, and the western part of Sichuan Basin and the eastern part of Northwest China are located in the west and northwest edge of WPSH.

Synergistic Effects of Bay of Bengal Tropical Cyclones and Tibetan Plateau Vortices on Water Vapor Transport over the Tibetan Plateau in Early Summer

The Bay of Bengal(BoB)tropical cyclones(TCs)and the Tibetan Plateau vortices(TPVs)are two crucial weather systems influencing the Tibetan Plateau(TP).Their synergistic effects can lead to widespread heavy precipitation events on the TP.In this study,we employ the Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model to track the trajectory of water vapor transport during three large-scale precipitation events on the TP under the combined influence of BoB TCs and TPVs.The results indicate that low-level water vapor from the BoB under the influence of BoB TCs was cyclonically entangled into the cyclonic circulation,lifted and transported northward by southwesterly flow to the southeastern part of the TP,which contributes to the moistening of the entire troposphere there.Additionally,convergence of the cyclonic circulation of the TPVs on the northern TP further transports water vapor collected in the southeastern TP northward,conducive to the maintenance and development of precipitation systems,thus inducing widespread heavy precipitation events over the TP.

Southwesterly Water Vapor Transport Induced by Tropical Cyclones over the Bay of Bengal during the South Asian Monsoon Transition Period

Based on best-track,outgoing longwave radiation,sea surface temperature,and reanalysis data during 1979-2018,statistical and composite analyses were performed to investigate characteristics of the southwesterly water vapor transport(WVT)induced by Bay of Bengal(BoB)tropical cyclones(TCs)during the South Asian summer monsoon(SASM)transition period.The results show that the BoB TCs mainly occur several days before/after the date of SASM onset(retreat)in May(October-November),thereby imposing an important impact on southwesterly WVT to China in those two periods.The WVT is significant in the middle and lower troposphere during the bimodal peak periods of BoB TCs,with large values over the east-central BoB,southeastern Tibetan Plateau,and Southwest and South China.The WVT is located more northward at 500 hPa than at 700 hPa,reaching close to 35°N and covering the southeastern Tibetan Plateau owing to weakening of the plateau’s blocking effect at upper levels.The BoB TCs mainly increase the northward and eastward WVT anomalies compared to the climatological mean.Furthermore,the large southerly WVT anomalies are located in the lower troposphere in low-latitude areas,while the large westerly WVT anomalies appear mainly in the middle troposphere in high-latitude areas.This indicates an enhanced WVT channel where the southwesterly moisture jet first climbs northwards to the southeastern Tibetan Plateau and then turns eastwards to East China under the influence of the BoB TCs.Besides,the southwesterly WVT during the TC period in May is stronger and more widespread than that in October-November,being about twice the latter in value.However,their maximum contributions to the climatological average do not differ much,with maximums of 12%and19%occurring in Southwest China during the bimodal periods,respectively,implying an important role played by the BoB TCs in the WVT.

Water Vapor Transport Related to the Interdecadal Shift of Summer Precipitation over Northern East Asia in the Late 1990s

In this study, an interdecadal shift of summer precipitation over northern East Asia （NEA） was identified, demon-strating that summer precipitation decreased abruptly after 1998/99. The synchronous shift in summer moisture budget and water vapor transport over NEA was further investigated by using the NCEP/NCAR reanalysis data. The results indicate that water vapor transported northward into NEA from three low-latitude paths was limited because most water vapor was transported eastward. Water vapor transported from the westerly path in mid-high （WMH） lat-itudes exhibited significant correlations with summer precipitation in NEA and experienced a significant adjustment in the late 1990s. Regarding the spatial distributions of water vapor transport, less input was found through the west-ern boundary while more output occurred through the eastern boundary of NEA, and zonal water vapor transport fluxes mainly concentrated at the low to middle levels, which led to the summer precipitation shift in NEA around the late 1990s. Furthermore, it is also confirmed that the wind anomalies （rather than the moisture disturbance） as the dominant internal dynamic factor and Pacific Decadal Oscillation/Atlantic Multidecadal Oscillation （PDO/AMO） as possible external force played important roles in influencing the water vapor transport and causing the summer pre-cipitation shift over NEA in the late 1990s.

The westerly fluctuation and water vapor transport over the Qilian-Heihe valley

The westerly fluctuation and the atmospheric water vapor transport over the Qilian-Heihe valley are analyzed and the results show that, in the water vapor transport stream field from Jun to September, this valley is in the westerly stream and the water vapor comes from westerlies water transport via the Black Sea and the Caspian Sea. The net water vapor transport is less net import and different from most areas of the northwest China. The interannual changes in water vapor transport over the valley arise from the westerly fluctuation, and have a positive relationship to the interannual changes in westerly wind speed. The cold air actions from the Mongol low pressure are the primary system that controls the westerly water vapor transport. Its action chain is that, the Mongol low pressure is strengthened → the circulation meridionality will be increased → the cold air will move southwards → the westerly will be stronger → the wind convergence of direction and speed will be stronger → the water vapor convergence transport will be increased → the local water vapor content will be increased. The interannual changes in atmospheric water vapor transport over the valley rely mainly on the convergence transport, but the effect of advection transport is less. The interannual changes of strong or weak westerly affect mainly the convergence transport, and then make the atmospheric water vapor net transport increase or decrease over the Qilian-Heihe valley.

THE STUDY ON EDDY TRANSPORT OF WATER VAPOROVER SOUTH CHINA

Water vapor transport is decomposed into mean transport and eddy transport. Analysis of watervapor over South China during the first flood season of 1994 shows that difference between season mean transport and season total transpoFt is less than 10%. For the monthly and ten-day averages, the difference is above it.The transient transport of water vapor is the least among all kinds of eddy transport. its amount is only 2% oftotal transpoft for column. The constant wave transport is the Iapest Sometimes it may be 1-6 times of totaltranspoFt.

Transport of Water Vapor over North China during the Drought Period in Summer of 1980

The features of water vapor transport, such as temporal evolution, vertical structure and spatial pattern, over North China during the prolonged drought in the summer of 1980 have been analyzed through computation of water vapor flux based on the once daily ECMWF grid-point data at 12GMT. The results indicate that it is unlikely that the characteristics of the atmospheric mass divergence, ascending motion and stratification stability in North China were completely opposite to those in the Yangtze River Valley, where the heavy flood occurred in the summer of 1980. It is major differences that the strong ascending motion and significant water vapor convergence overlap fairly well each other in the vertical levels in the Yangtze River Valley, while the maximum ascending motion is accompanied by water vapor divergence or weak water vapor convergence in North China. This vertical structure in North China results in insufficient water vapor supply and, therefore, little condensation and precipitation in the middle and upper atmosphere were produced. Additionally, a mode of monthly-scale low frequency oscillation can be found in water vapor flux, which is in correspondence to the fluctuation period of rainfall.

Spatiotemporal Variation of Water Vapor Budget over the Tibetan Plateau and Its Regulation on Precipitation

The spatiotemporal variations of water vapor budget(Bt)and their relationships with local precipitation over the Tibetan Plateau(TP)are critical for understanding the characteristics of spatial distributions and evolutions of water resources over the TP.Based on a boundary of the TP,this paper explored the spatiotemporal characteristics of Bt over the TP using the European Centre for Medium-Range Weather Forecasts interim(ERA-Interim)reanalysis datasets.On the climatological mean,the TP is a water vapor sink throughout four seasons and the seasonal variation of Bt is closely associated with the water vapor budget at the southern boundary of the TP.The transient water vapor transport is quasimeridional in the mid-and high-latitude areas and plays a leading role in winter Bt but contributes little in other seasons.At the interannual timescale,the variation of Bt is mainly determined by anomalous water vapor transports at the western and southern boundaries.The Bay of Bengal,the North Arabian Sea,and mid-latitude West Asia are the main sources of excessive water vapor for a wetter TP.At the southern and western boundaries,the transient water vapor budget regulates one-third to four-fifths of Bt anomalies.Moreover,the variability of the TP Bt is closely associated with precipitation over the central-southern and southeastern parts of the TP in summer and winter,which is attributed to the combined effect of the stationary and transient water vapor budgets.Given the role of the transient water vapor transport,the linkage between the TP Bt and local precipitation is tighter.

Diagnosing anomalous characteristics of atmospheric water cycle structure during seasonal-scale drought events:A case study in middle and lower reaches of Yangtze River

Anomalous characteristics of the atmospheric water cycle structure are highly significant to the mechanisms of seasonal-scale meteorological droughts.They also play an important role in the identification of indicative predictors of droughts.To better understand the causes of seasonal meteorological droughts in the middle and lower reaches of the Yangtze River(MLRYR),characteristics of the atmospheric water cycle structure at different drought stages were determined using standardized anomalies.The results showed that the total column water vapor(TCWV)was anomalously low during drought occurrence periods.In contrast,there were no anomalous signals at the drought persistence and recovery stages in the MLRYR.Moreover,there was no significant temporal correlation between the TCWV anomaly and seasonal-scale drought index(the 3-month standardized precipitation index(SPI_(3))).During drought events,water vapor that mainly originated from the Bay of Bengal was transported southwest of the MLRYR.Meanwhile,the anomalous signal of water vapor transport was negative at the drought appearance stage.At the drought persistence stage,the negative anomalous signal was the most significant.Water vapor flux divergence in the MLRYR showed significant positive anomalous signals during drought events,and the signal intensity shifted from an increasing to a decreasing trend at different drought stages.In addition,a significant positive correlation existed between the anomaly of water vapor flux divergence and regional SPI_(3).Overall,water vapor flux divergence is more predictive of droughts in the MLRYR.

Low-frequency variability of terrestrial water budget in China using GRACE satellite measurements from 2003 to 2010

Mass variations in terrestrial water storage（TWS） obtained from eight years of satellite data from the Gravity Recovery and Climate Experiment（GRACE） are used to describe low frequency TWS through Empirical Orthogonal Function（EOF） analysis. Results of the second seasonal EOF mode show the influence of the Meiyu season. Annual variability is clearly shown in the precipitation distribution over China, and two new patterns of interannual variability are presented for the first time from observations, where two periods of abrupt acceleration are seen in 2004 and 2008. GRACE successfully measures drought events in southern China, and in this respect, an association with the Arctic Oscillation and El Nino-Southern Oscillation is discussed. This study demonstrates the unique potential of satellite gravity measurements in monitoring TWS variations and large-scale severe drought in China.