东亚副热带西风急流的时间演变特征及其与中国东部夏季降水的关系

为深入了解东亚副热带西风急流与中国天气系统之间的联系，利用1961-2007年美国国家环境预报中心（NCAR／NCEP）再分析月资料和同期中国596站的降水资料，运用经一纬向急流轴和区域平均两种定义方法分析了西风急流的时间演变特征及其与中国东部降水型的关系，结果表明：（1）两种方法对西风急流东西、南北位置转折时段的分析很接近，分别出现在20世纪80年代和70年代；对西风急流强度、南北位置周期的表征也很一致，分别为10-15年和5-10年。（2）当西风急流位置偏北（南）时，东部地区整层大气环流呈“南北上升中间下沉（南北下沉中间上升）”的形势，850hPa的流场和水汽通量输送都有利于华北地区（江淮河流）的降水，易于形成“南北多中间少（南北少中间多）”的雨带分布，推测这两种反相位雨型的间隔时间为2．5-5年；相比之下，急流东西位置和强度的周期性变化与东部局地降水存在一定联系。

Temporal Evolvement Characteristics of East Asia Subtropical Westerly Jet and Its Relationship with the Summer Precipitation over Eastern China

In order to interpret the association between the subtropical westerly jet and the weather system of China, the differences and temporal evolvement characteristics between westerly jet index （WJI） and zonal-meridional west- erly jet axis in the East-Asia subtropic area and their relationships with the summer precipitation over eastern China are investigated by using the NCEP/NCAR reanalysis monthly mean data from 1961- 2007. It is shown that： （1） The interannual changes of westerly jet for the different defining ways are almost the same. The interannual crisis for the westerly jet meridional and zonal position happened in 1980s and 1970s of last century respectively. The period of the westerly jet intensity and westerly jet meridional position（WJMPI） are all 10 - 15a and 5 - 10a for the two differ- ent methods, respectively. （2） We also find that while westerly jet is abnormally northward （southward）, sufficient water vapor supply at 850hPa appear in North China（Yangtze-Huaihe basin）, which are related to the more （less） summer precipitation in South and North China and less （more） precipitation in Yangtze River. The happening of these two distribution of precipitation usually have a 2 - 2.5a interval by inferring from the period of the WJMPI. Meanwhile, the westerly jet intensity is stronger （weaker） than normal,which is related to more （less） summer pre- cipitation in North China and less （more） precipitation in Southeast China; the westerly jet is abnormally eastward （westward） ,which is related to less （more） summer precipitation in western part of South China and more （less） precipitation in eastern part of Northwest China.