Key District Of The Middle And Low Latitude Water Vapor Transport To The Structural Characteristics Of The Yangtze River Valley Summer Rainfall Anomalies

Water cycle variations is the hot point for international researches. It is very necessary to discuss the characteristics of moisture transport structure in mid-lower latitude key region (MLLKR) and its impact on anomalies of summer precipitation in Yangtze River Valley(YRV). In virtue of synthetical statistic methods, this paper analyzes the climatological features of moisture transport in MLLKR, to reveal the feature of teleconnection moisture transport source/sink structure of Meiyu rain belt in MLLKR from 25-year long time simulation experiments. And we research influence effects of"moisture source"of East Indian Ocean(EIO)-South China Sea(SCS) on Meiyu precipitation by using methods of diagnosis and simulation. In addition , we also discuss the effect of subgrid topography of Tibetan Plateau and its peripheral areas on moisture transport structure and downstream summer precipitation. Finally, we research the differences of moisture budget in MLLKR for drought/flooding years of YRV and give the physical figure of atmospheric water cycle variation for drought/flood anomalies of YRV in MLLKR. The Main conclusions are as follows:(1) Putting forward the key region of moisture transport that influence drought and flood of China which is called MLLKR of moisture transport (MLLKR, in short). It includes Tibetan Plateau ,Eastern China ,EIO and West Pacific(about 10o～35oN,80o～130oE). The differences of moisture content and meridional moisture transport between summer and winter are very significant, the extent of variation of summer meridional/zonal moisture transport is also significant in this region.The feature of moisture transport in MLLKR can embody the circulation structure of monsoon system and its seasonal feature is obvious. In summer, the meridional moisture transport intensify remarkably and there exist three branch flows of strong south wind moisture transport, namely the flow of southwest monsoon in Bay of Bengal(BOB) and north around it, the flow of SCS monsoon from SCS to Eastern China and the southeast wind flow in East Sea, and a regional center of strong west wind transport in region of Indian Ocean(IO)-BOB-SCS. In winter , there are also three branch flows of north wind moisture transport and they locate at west of BOB, east to Indo-China Peninsula(ICP) and the south to Philippine.(2) The spatial-temporal evolution features of the first eigenvector of interdecadal component of moisture transport in summer in East Asia are the one of key reasons that make the interdecadal variation of summer precipitation of Eastern China to change from"south-drought and central-flooding" to"south-flooding and north-drought", namely, make the summer rain belt of Eastern China to display southerly shift.(3) There exist the inverse-phase feature of the moisture transport source/sink structure of Meiyu rain belt (the departure of moisture transport flux) in MLLKR for drought/flooding years of YRV, it shows that the far distance moisture transport flow pattern in the area of SCS-Tibetan Plateau-Yangtze River valley in flooding years and it is reverse in drought years from the 25-year long time simulation experiments.The experiments of influence effects of EIO-SCS moisture source reveal the moisture source of EIO-SCS play a significant role of Meiyu Precipitation and the variations of its intensity will make corresponding significant variations of Meiyu precipitation.(4) The experiments of topographic scale influence effects over Tibetan Plateau reveal that the uneven distributions of moisture transport have significant correlation to small scale"valley groups"topography over Tibet. The result of the experiments also disclose the"upstream topography-scale structure forcing effect"may produce the teleconnction influence effects on Meiyu precipitation of YRV.(5) Southeast of Tibetan Plateau , as the moisture transport channels to eastern of Northwest China and middle and lower reaches of Yangtze River Valley(MLRYRV) plays an important role on the moisture budget around its areas. The westerly moisture transport flows are remarkable strong and northerly moisture transport flows are significant weak in flooding years of MLRYRV, reverse to drought years. The region ,as a"transferring station", is the one of key factors to flood anomaly in MLRYRV and drought anomaly in North China.(6) There exist anti-cyclone/cyclone form of moisture transport chain structure in moisture budget"box-latticework web"structure of MLLKR for flooding/drought years of YRV in summer/spring. The teleconnection structure feature of moisture transport of spring may look as one of portentous signals of summer precipitation in YRV.In summer, the moisture flow between the boundaries of moisture budget"box-latticework web"displays SCS-ICP-BOB-south side of Tibetan Plateau-MLRYRV-East Sea compositive transport physical diagram during flooding years of YRV and East Sea-MLRYRV-south side of Tibetan Plateau-BOB-ICP-SCS compositive transport physical diagram during drought of YRV.Under the East Asian monsoon weakening background in the 1980s and 1990s, the trend of anti-cyclone form moisture transport chain is enhancing. The trend of anti-cyclone form of moisture transport chain is the same to interdecadal change trend of"south-flooding and north-drought"for summer precipitation over Eastern China.