中文摘要：

对1958-2000年亚洲纬向风和我国160站夏季降水进行SVD分析，发现两者具有良好的耦合关系。根据分析结果定义了一个可以表征我国夏季降水的亚洲夏季西风指数（IASW）。西风指数高（低）年，长江中下游夏季降水偏少（多），华南、河套和东北地区降水偏多（少）。同时分析了高、低西风指数年的环流特征，发现当长江中下游夏季降水偏多而华南、河套和东北地区降水偏少时，500hPa呈负EAP型，鄂霍茨克海和乌拉尔山有阻高建立，西太平洋副热带高压偏南，105°E越赤道气流偏弱，东亚夏季风偏弱，高纬的偏北气流和低纬的偏南气流在我国长江中下游地区汇合，梅雨锋加强，使得雨带在此维持。前期鄂霍茨克海区域平均位势高度以及前期1-3月西太平洋的热带对流活动可以作为预测夏季西风强弱的前兆信号。

英文摘要：

The relationship between zonal winds in Asia and the 160-station summer rainfall in China for the period of 1958-2000 is analyzed by employing the SVD method, and based on the analysis results, the Asian summer westerly index（ IAsw） is then defined as the 500 hPa zonal wind averaged over （60 - 150°E,40 -50°N） to represent the summer rainfall in China. It is shown that high IAsw year relates to less summer rainfall in the mid and lower reaches of Yangtze River and more summer rainfall in south China, the mid-reaches of the Huanghe River and Northeast China; and vice versa. We also find that when the summer precipitation is excessive, there is a negative EAP pattern in 500 hPa geoPotential heights i. e. blocking highs are built over the Okhotsk sea and the Ural mountains;the west Pacific subtropical high lies south of normal ,and the cross-equatorial flow of 105°E and the East Asian summer monsoon are weaker; and the northerly flow from higher latitudes meets the southerly flow from lower latitudes in the mid and lower reaches of the Yangtze River,leading to the strengthening and maintenance of meiyu front. This study indicates that the regional mean geopotential height over the Okhotsk sea in early stage, and the convection over the west Pacific 1-3 months in advance could be used to predict the strength of the Asian summer westerly.