东亚高空西风急流与东亚-西太平洋夏季风降水异常关系的年代际变化

Interdecadal changes in the relationship between East Asia-West Pacific summer monsoonal precipitation anomalies and East Asian upper-tropospheric westerly jet stream

东亚副热带西风急流(East Asian Jet Stream,EAJS)的经向位移对东亚-西太平洋夏季风降水活动有着重要影响。利用前人定义的EAJS经向位移指数(East Asian Jet Stream Index,EAJSI),发现盛夏(7、8月)EAJSI的年际变率在1990s末期经历了一次显著的年代际变化。而且EAJSI与东亚-西太平洋盛夏降水之间的关系自1999年以来显著减弱。在1980-1998年盛夏,与EAJSI相关的东亚-西太平洋降水异常呈典型的三极型模态,而这种相关关系在1999-2017年盛夏期间几乎消失了。其可能的原因是由于大尺度的大气-海洋环境年代差异,使得东亚-太平洋型/日本-太平洋型(East Asia-Pacific/Pacific-Japan,EAP/PJ)低频遥相关波列在1990s末期之后明显减弱和东移。这导致了盛夏EAJS经向位移的幅度显著减弱,进而引起EAJSI和东亚-西太平洋夏季风降水异常之间的关系转变。

Meridional displacement of the East Asian Subtropical Westerly Jet Stream(EAJS)plays an important role in the East Asia-West Pacific(EA-WP)summer monsoon/precipitation activity.By using the EAJS-meridional displacement index(EAJSI),it is found that the interannual variability of EAJSI during mid-summer(July-August)has experienced a notable interdecadal change in the late-1990s.Besides,the relationship between EAJSI and EA-WP precipitation are correspondingly weakened significantly since 1999.Compared with the classical tripole mode of the EA-WP precipitation anomalies linked to EAJSI during mid-summer for 1980-1998,such relationship has almost disappeared during 1999-2017.Further analysis suggests that the possible reason is that the EAP/PJ(East Asia-Pacific/Pacific-Japan)teleconnection wave-train has significantly weakened and shifted eastward after the late-1990s due mainly to the interdecadal differences of the large-scale atmospheric-oceanic environments.As a result,the amplitude of the meridional displacement of EAJS has significantly weakened,leading to the shifting correspondence between EAJSI and summer monsoonal precipitation anomalies over the EA-WP.