夏季区域西风指数对中国西北地区水汽场特征影响的对比分析

Influences of Westerly Wind Interannual Change on Water Vapor Transport over Northwest China Summer

利用1970—1997年NCEP/NCAR再分析月平均资料,设计了区域西风指数。通过分析西北地区夏季的水汽输送通量散度,发现该地区水汽平流引起的水汽输送通量散度项年际变化极小,而风场辐合(辐散)引起的水汽输送通量散度项年际变化却很大,在西北地区区域西风指数较强年份风场辐合比区域西风指数较弱年份强。由此可知,西风年际变化对西北地区的风场辐合(辐散)的影响是我国西北地区水汽场年际变化的主要原因。

The zonal index and the divergence of summer water vapor transport flux over Northwest China are analysed by using NCEP/NCAR monthly mean reanalysis data from 1970 to 1997. The analysed results show that the interannual change of moisture flux divergence resulted by moisture advection is constant, but resulted by wind field convergence or divergence is unstable. The wind field convergence is stronger in strong west wind years. So we can conclude that the interannual changes of summer water vapor over Northwest China is mainly resulted by wind field convergence or divergence.