WATER VAPOR CONTENT AND MEAN TRANSFER IN THE ATMOSPHERE OVER NORTHWEST CHINA

The interannual and intermonthly climatic features of the water vapor content(hereafter WVC) and its mean transfer in the atmosphere over Northwest China(hereafter NWC) are calculated and analyzed by using the NCEP/NCAR global reanalysis grid data(2.5°×2.5°Lat/Lon) for 40 years(1958-1997).The results show that the WVC in the total air column over NWC in four seasons of the year is mainly concentrated on eastern and western NWC respectively.On the average,the WVC over eastern NWC decreases obviously during recent forty years except for winter.while it decreases over western NWC in the whole year.But the WVC over NWC has been increasing since late 1980s in summer.The water vapor comes from the southwestern warm and wet air current along the Yarlung Zangbo River Valley and the Bay of Bengal.and from mid-western Tibetan Plateau and also from the Qinling Mountains at southern Shaanxi Province.The yearly water vapor divergence appears over the middle of NWC to northern Xinjiang and southeastern Shaanxi Province.The yearly water vapor convergence appears over the Tarim Basin and the Tibetan Plateau as well as western Sichuan and southern Gansu.