影响华北汛期降水的水汽输送过程

利用1951～2005年NCEP再分析资料和中国160站月降水资料，分析了华北汛期水汽输送的时空特征及其与降水的关系，发现不同水汽通道对华北降水的影响区域不同。华北的水汽输送也具有明显的年际变化，华北多雨年和少雨年的水汽通量分布有明显差异。EOF分析表明，在华北汛期多雨年，上述水汽通道有向华北地区的正异常水汽输送。华北汛期水汽主要来自亚洲季风水汽输送，其次是西风带的水汽输送，它们与降水具有相似的年代际变化。1970年代中期以后，季风的水汽输送显著减弱，西风带水汽输送的重要性相对增大，华北降水在1980年代初的突变与季风水汽输送1970年代中期的突变密切相关。

Features of Moisture Transport Associated with the Precipitation over North China during July-August

The July-August Asian monsoon moisture transport and its relationship with the rainfall over North China have been investigated using NCEP/NCAR monthly mean reanalyses and precipitation data of 160 stations in China over 1951-2005.Results show that different moisture paths connect with different regional rainfall in North China,respectively.The features of moisture fluxes in North China rainy season with more rainfall are quite opposite to that with less rainfall.Experience Orthogonal Function(EOF) analysis describes that anomalous influxes through every moisture path to North China correspond to the positive rainfall anomaly over this region,and vice versa.The Asian monsoon contributes much more than the westerlies in terms of vapor transfer into the North China.Both moisture influxes are closely related to the rainfall in North China on the interdecadal time scale.The moisture transfer by Asian monsoonal currents underwent an abrupt weakening at the end of the 1970s which was in connection with the distinct decrease of precipitation over North China from the beginning of the 1980s and gave relative emphasis to the westerly moisture transfer associated with rainfall over North China.