夏季东亚副热带经圈环流特征及其对长江流域降水的影响

CHARACTERISTICS OF SUBTROPICAL MERIDIONAL CIRCULATION IN EAST ASIA AND THEIR INFLUENCES ON PRECIPITATION OVER YANGTZE RIVER BASIN

利用NCEP/NCAR 1979—2009年月平均风场资料,用质量流函数来定义东亚副热带的经圈环流指数,分析夏季(6—8月)东亚副热带经圈环流特征。结果表明,夏季东亚地区受反Hadley环流影响,表现出与全球平均经圈环流不同的特征,用指数表征的东亚副热带经圈环流强度存在明显的年际和年代际变化。另外,利用相关性及水汽通量分析,研究了经圈环流对同期长江流域降水的影响,表明环流指数与长江流域的降水存在较好的对应关系,指数强(弱)年的降水偏多(少),7月最为明显。

With the 1979—2009 NCAR/NCEP reanalyzed data,an East Asia subtropical meridional circulation index is defined by using mass stream function,and the characteristics of meridional circulation in summer are studied.The result shows that East Asia is affected by counter Hadley circulation in summer and has different features with mean meridional circulation,and the subtropical meridional circulations in East Asia present obvious interannual or interdecadal variations.In addtion,correlation and water vapor flux are analyzed,and it shows that there is a good relationship between the circulation index and precipitation over Yangtze River basin,the stronger（weaker） circulation index corresponds to the more（less） rainfall over Yangtze River basin,especially in July.