中国西部空中水汽分布结构特征

利用1958-1997年月平均NCEP比湿资料研究了中国西部空中水汽分布特征。结果表明：水汽的垂直分布结构非常相似，850hPa以上的水汽分布中心位于青藏高原上空，5-10月水汽含量主要集中在500hPa以下，其中7月的空中水汽含量最丰沛。水汽含量随高度减少，从季节变化来分析，夏季最大、秋季次之、冬季最小。40a的水汽年代际变化表明，夏季空中水汽含量呈现线性下降趋势，特别是20世纪90年代以来更明显；冬季比湿呈线性上升趋势，1月和7月比湿的年代际变化趋势呈反位相特征。

Distributive Characters of Water Vapor in Western China

Distributive characters of water vapor in Western China are analyzed in this paper by using the NCEP monthly mean specific humidity data from 1958 to 1997. Analysis results show that the structure of the vertical distributions of water vapor is very similar, the center of water vapor above the 850 hPa level laid over the Qinghai-Xizang Plateau,and the water vapor content mainly concentrated in the lower atmosphere below the 500 hPa level in May to October in a year, especially in July moisture was most abundant. The content of water vapor reduced obviously with altitude. It was largest in summer, next in autumn, and smallest in winter. The interdecadal variations of moisture in the recent 40 years show that summer moisture has linearly reduced, especially since the 1990s;while winter specific humidity has linearly increased;and the interdecadal trends of January and July specific humidity were oppsite in phase.