Northwest Atmospheric Moisture Characteristics And Related Issues A Preliminary Study

By utilizing the NCEP/NCAR reanalysis gridded specfic humidity data during 1951.1 to 2000.12, firstly, the evolution features of the whole troposphere over Tianshui and Wulumuqi , which are respectively in the east and west of Northwest China (NWC ) , was investigated and contrasted with what in other places in the same latitude over the North-hemisphere. Secondly, the mean seasonal climate characteristics of atmosphere water vapor and its transport flux over NWC respectively in January, April, July and October during the past 50 years was discussed. Lastly, the Precipitable Water (PV) and vapor transport flux during the great drought affair in the east of NWC in 1990s' have been analyzed and compared with what during wet years. The reason that resulted to that drought affair was studied from the point of water vapor in the atmosphere. The main results are as follows:(1) The evolutionary features of precipitable water in the whole troposphere in Northwest China are different between over the east region and over the west region during the past 50 years from 1951-2000: in the 1990s' the PV in the east of NCW is evidently decreased , and the scope of the descent is the largest one in the same latitude over the North-hemisphere , on the contrary, which in the west regions showed increasing trend . That is to say , the so-called drought trend in the east of NWC , is not only point to the evolution of precipitation on the ground in the long term, but also to the vapor content in the whole troposphere. The different trends of PV between east region and west region are consistent with what of precipitation.(2) The yearly vapor water transport in Northwest China is mainly consist of the west-southly air stream from the center-west of Qinghai-Xizang Plateau and the east-southly air stream from the South of Shanxi province. In the whole year, the air stream always convergent in Talimu Basin, Qinghai-Xizang Plateau and the north of Sichuan Plateau; there is no marked convergence or divergence signal in the North of Xinjiang; the air stream over the center and east of Northwest is always divergent.(3) The mean features of vapor water in the atmosphere in the east of NWC between during the great drought affair and dry years are contrasted and shows that, the Precipitable Water in the whole troposphere is evidently reduced, and the vapor transport is also weakened, the degree of convergence of water vapor is lessened. All these facts play against the production of precipitation.(4) The intensity of the vertical movement of the air over the east of NWC, from the 1990s', it tended to weaker, which is regarded as a dynamic background condition.