The Study To The Relation Of West China Vapor Transportation And Flood/Drought

By using of monthly rainfall of 743 stations and NCEP/NC AR reanalysis monthly data , firstly , the distribution characters of whole layer and 500Hpa monolayer specific humidity and vapor transportation fluxes in west China are analysed;secondly , dividing the west China into the eastern northwest ,the central northwest, southern Xinjiang , northern Xinjiang , Tibet , Qinghai , the paper analyses the relation of the rainfall in summer and water vapor , discusses the abnomal characters in drought/flood years , reveals the sourses of water vapor in western regions;lastly, puts the emphase in the rainfall and water vapor of Qinghai-Tibet Plateau composed of north and south parts . The results are that:(1) The vertical distribution of water vapor from 850Hpa to 300Hpa are resemblance , whose centers are located in near the Qinghai-Tibet Plateau . The changeable features of specific humidity in season are : it is biggest in summer, less in spring , least in winter.(2) In spring , the whole layer vapor transportation fluxes of west China are mainly from mid-Asia;in summer , the water vapor of the bay of Bengal is stronger , there is lots of vapor through the stream valley to the southeast of Qinghai-Tibet Plateau and the south China Sea . In this time , the vapor in west China is lesser , moreover , principally comes from the inland of China and transits to the east;in autumn , the vapor of Plateau is from its western regions and the bay of Bengal , other areas are almost westerly vapor transportation;the vapor is least in winter and nearly westerly transportation .In 500Hpa , the averagely vapor transportation in west China are mainly in zonal transport . The vapor of southwest is from southwest monsoon, and the vapor of northwest comes from westerly transport.(3) The correlation of the rainfall of eastern northwest in summer and water vapor reveals that the rainfall is mainly from westerly vapor transportation and mid-latitude Pacific Ocean . meanwhile, it is relation to the vapor of the low-latitude Ocean . in its drought years , the westerly vapor transportation in mid-latitude amplify obviously , while in flood years northward vapor transport of Plateau eastern areas strengthen . The result shows the precipitation in summer of eastern northwest is related to southwest vapor transport . The correlation of rainfall of the mid-west northwest in summer and water vapor shows the rainfall comes from the westerly vapor transport of the Atlantic Ocean and the Arctic Ocean .(4) Totally, the rainfall of Qinghai-Tibet Plateau increases during the last four decades , in which the years 1961-1980 is less rain perid , 1981-2000 is morerain perid . In spring and winter the rainfall of Plateau is increasing tendency , while in summer and autumn the rainfall changes little . The rainfall of the southern Plateau also presents increasing tendency .(5) The analysis to the correlation of the rainfall in Tibet and specific humidity & vapor transportation fluxes reveal that the vapor in spring from the low-latitude ocean has some impacts to the precipitation in summer , and the vapor in summer that impacted the area is from the low-latitude ocean and westerly transport. In the drought years , the westerly vapor transport and the northward vapor transport from the bay of Bengal weaken obviously , while in the flood years , the vapor toward northeast from the north Indian Ocean and the westerly vapor transport strengthen , the northward vapor from the bay of Bengal strengthen obviously too .(6) The analysis to the correlation of the rainfall in Qinghai and specific humidity & vapor transportation fluxes reveal that the vapor in summer is from the south China Sea and the north china , In the drought years , the eastward vapor transport from the Plateau strengthen , while the westerly vapor transport from the north of Plateau weaken . In the flood years , the vapor toward north from the Plateau strengthen , maybe it relates to the reinforcement of subtropical high.