三江源地区春夏季降水与太平洋海温的关系

从预测三江源地区春季、夏季降水趋势的需要出发,利用聚类分析法将三江源地区春、夏季降水场分为3个区域。通过对3个区春、夏季降水指数与前期太平洋海温相关普查,定义了与3个区春、夏季降水指数相关的海温分布型指数。冬季西太平洋海温偏低(偏高),赤道中、东部太平洋海温偏高(偏低)的海温分布型造成三江源1区、3区春季降水减少(增加);冬季赤道太平洋中部、加利福尼亚海域海温偏高(偏低)的海温分布型造成2区、3区夏季降水减少(增加)。对冬季太平洋海温分布型与后期春、夏季500 hPa北半球高度场的相关分析结果表明:当冬季西太平洋海温综合指数高(低)时,春季高度场印度高压、中西伯利亚槽及阿留申低槽加强(减弱),三江源地区春季降水偏少(偏多);而当冬季太平洋中部、加利福尼亚海域海温综合指数高(低)时,夏季高度场伊朗高压、中西伯利亚高脊加强(减弱)及西太平洋副高位置偏南(偏北),夏季降水偏少(偏多)。

Relationship between Spring and Summer Rainfall in Three River Source Region and Pacific SST

The clustering analysis method is employed to divide the rainfall field in spring and summer over the Three-River Source region into three areas for predicting the rainfall distribution and rainfall trends for different areas.Based on the correlation relationship of the spring and summer rainfall indexes in the three areas with the Pacific SST in the preceding season,the SST distribution index is defined.When the winter SST over the western Pacific is lower(higher) than normal,the higher(lower) than normal SST distribution in the central and eastern equatorial Pacific is correlated with the decreased(increased) spring rainfall in Areas 1 and 3 of the Three-River Source Region;while the higher(lower) than normal winter SST distribution in the central equatorial Pacific and off the coast of California is correlated with the decreased(increased) summer rainfall in Areas 2 and 3 of the Three-River Source region.Further analyses are conducted of the correlation relationship between the winter SST in Pacific and the spring and summer 500 hPa geopotential height field in the Northern Hemisphere.The results show that when the overall winter Pacific SST index is high(low),the Indian high pressure system,central Siberia trough and Aleutian trough at 500 hPa in spring strengthen(weaken) with increased(decreased) spring rainfall in the Three-River Source region.In contrast,when the overall winter SST index in the central Pacific and off the coast of California is high(low),the Iranian high pressure system and central Siberia ridge in summer strengthen(weaken) with the southward(northward) displacement of the western Pacific subtropical high and decreased(increased) summer rainfall in the Three-River Source region.