夏季东亚高空副热带西风急流季节内异常的环流特征及前兆信号

Anomalous Circulation Characteristics of Intraseasonal Variation of East Asian Subtropical Westerly Jet in Summer and Precursory Signals

位于东亚中纬度上空的东亚高空副热带西风急流是东亚季风环流系统中的重要成员,我国夏季降水雨带的季节内变化受东亚高空副热带西风急流位置季节内异常变化影响。根据1979~2008年中国降水资料、NCEP/NCAR再分析资料以及NOAA ERSST V3月平均海表温度资料,利用统计分析和物理量诊断方法对夏季东亚高空副热带西风急流位置季节内异常的东亚大气环流特征及外强迫信号的物理过程进行了探讨。研究指出:6月东亚高空副热带西风急流位置异常主要受欧亚大陆中高纬东传的Rossby波列位相变化影响,春季北大西洋海温异常是欧亚大陆中高纬度Rossby波列位相变化的最显著的外强迫信号;7月东亚高空副热带西风急流位置异常主要受西太平洋热带向副热带传播的Rossby波列位相变化影响,春季西太平洋热带海温异常是西太平洋热带向副热带传播的Rossby波列位相变化的最显著的外强迫信号;8月东亚高空副热带西风急流位置异常主要受南亚大陆向东亚大陆热带、副热带传播的Rossby波列位相变化影响,春季印度洋海温异常是南亚大陆向东亚大陆热带、副热带传播的Rossby波列位相变化的最显著的外强迫信号。

The EASWJ（East Asian Subtropical Westerly Jet） is one of the most important circulation systems in East Asia, which links the high and low latitude circulations over East Asia. The intraseasonal variation of position and intensity of EASWJ during June, July, August and the East Asian circulation characteristics as well as the physical processes are discussed by using statistical analysis and physical process diagnosis methods based on the NCEP/NCAR reanalysis data and NOAA ERSST V3 monthly mean sea surface temperature（SST） data from 1979 to 2008. The physicalmechanism for intraseasonal shift of the EASWJ is explored. The study points out that in June, the position shift of the EASWJ is affected by the phase variation of eastward propagating Rossby waves in the Eurasian continent. The North Atlantic SST anomalies（colder or warmer than normal） in spring are the most significant forcing signal for the phase variation of Rossby waves in the Eurasian continent. In July, the position shift of the EASWJ is affected by the phase variation of Rossby waves propagating northward from the tropical to subtropical western Pacific. The tropical western Pacific SST anomalies in spring are the most significant forcing signal for the phase variation of Rossby waves over the western Pacific. In August, the position shift of the EASWJ is affected by the phase variation of Rossby waves propagating northward from South Asia to tropical and subtropical East Asia. The Indian Ocean SST anomalies in spring are the most significant forcing signal for the phase variation of Rossby wave propagating from South Asia to tropical and subtropical East Asia.