| The climatic characteristics of the Moist Pool over the Tibet Plateau are comparatively analyzed with two reanalysis-datas of ERA-Interim(shortened as ERA) and NCEP/NCAR2(shortened as NCEP2) and radiosonde observation data,then the temporal and spatial variations of water vapor content of the Moist Pool based on EOF and its possible causes of change are studied by ERA data,at last,the characteristics of water vapor budget of the the Moist Pool regions and their relationships with precipitation in China in both summer and winter are also studied.The results are as follows:(1) The high water vapor centers,that is the Moist Pool,exist both in summer and winter over the middle-upper troposphere. The Moist Pool has the strongest intensity in summer(July),in addition to the existence of continuous wet centers of precipitable water vapor in the southern highlands of the Plateau, there is a wet center in the northwestern part of the Plateau by ERA data, but wet centers only exist in southeastern and southwestern areas of the Plateau by NCEP2 data. In winter(January), there are only wet center in the southeast of the Plateau by both data. The ERA data is more close to radiosonde observation data on the whole.In July, the intensity of the centers in the southern highlands by ERA data are stronger than NCEP2 data,they are continuously stronger since the mid-1990s(1994~1996 years),and the northwest center has alternating characteristics between weaker and stronger.The intensity of the centers in the southern highlands by NCEP2 data are stronger since 2009 and 1998 respectively. In January,the centers almost have the same intensity by both data,they are continuously stronger since the late-1980 s and mid-1980 s respectively. In July,the high water vapor centers in southern region of the Plateau are almost continuous areas by ERA data, and this feature is more obvious since 1996,while NCEP2 data has two longitudes zones. But it has two wet centers zone in January by both datas.(2) Based on the EOF analysis,the abnormality of water vapor content of the Moist Pool presents the whole Plateau consistent-type,the west-east opposite-type and the north-south opposite-type in summer,three types has cycles of 4~6 years.And in winter,it presents the whole Plateau consistent-type,the north-south opposite-type,two types has cycles of 3~6 and 10 years.The types in summer and winter can indicate the precipitation of China.In abnormally positive(negative) years of time coefficient of the first convector,the Southern Trough is weaker(stronger),the South Asia High is weaker(stronger),water vapor isn’t(is) favorable to be transported to the Plateau and is convergent in summer,which make less(more) water vapor content of the Moist Pool.In winter,the Southern Trough is stronger(weaker),the East Asian Trough is stronger(weaker),water vapor is(isn’t) favorable to be transported to the Plateau and is convergent,which make more(less)water vapor content of the Moist Pool, this reflects the main change causes of the Moist Pool.(3) In summer,water vapor inputs the southeastern region of the Moist Pool from the western and southern boundary, outputs from the eastern and northern boundary. Net vapor budget is "surplus", with net vapor input and net vapor output,they have obvious trend of mutation between 1993/1994,and all have about 4-6-years cycles.The water vapor transmission field in Asia has two opposite wavetrains along NNW-ESE and WSW-ENE before and after 1993/1994 mutation, their intersection and interaction make the precipitation of China appear the opposite distribution from north to south.The net water vapor input(output) of this region in summer is positively related to the same period of precipitation of the whole regions from southeastern Tibet Plateau to Yangtze-Huaihe River basin and North China, and is negatively related to that of South China.The precipitation distribution is “+-”(“-+”)type from north to south in China during abnormal more(less) water vapor output years,that is positive(negative) abnormality along Yangtze-Huaihe River basin and in North China and is negative(positive) abnormality in South China,and the water vapor transportation is favorable for the more precipitation regions.The water vapor transportation of the southern boundary in summer can indicate the precipitation of the northwestern region,Yangtze-Huaihe River basin and South China in autumn.(4) In winter,water vapor inputs the high water vapor content region from the western and southern boundary and outputs from the eastern and northern boundary.Net water vapor budget is "surplus" in the high water vapor content region on average from 1979 to 2012. The trend of net water vapor input as well as net water vapor output is increasing while the trend of net water vapor budget is decreasing,but they all have about 4-6-years cycles.Net water vapor input of the high water vapor content region in winter can instruct the precipitation of southern Xinjiang,from eastern Tibet Plateau to Sichuan basin and Yunnan-guizhou plateu,net water vapor output can instruct the precipitation from southwestern China to South China,that is the most regions in southern China,while net water vapor budget can reflect the precipitation of eastern Tibet Plateau and its adjacent areas, middle reaches of the Yangtze River basin.The precipitation in most regions of southern China is less(more) than normal during abnormaly more(less) water vapor output years in the high water vapor content region,and water vapor transmission arn’t(are) favorable to be transported to southern China and converged,this shows that the strength of the water vapor output in this region reflects the strength of water vapor transportation and the distribution of precipitation in south China, and it also indicates the way how the water vapor budget effects the precipitation by means of circulating. And the water vapor budget of this region in winter can indicate the precipitation of the middle-Inner Mongolia,Yangtze-Huaihe River basin,northern areas of northeastern China, and eastern areas of northwestern China in spring. |
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