东亚冬夏季风关系在1970s末的年代际转变

The decadal change of relationship between East Asian winter monsoon and East Asian summer monsoon in late 1970s

利用NCEP/NCAR和Hadley中心的大气与海洋再分析资料,选取具有代表性的东亚冬、夏季风指数,采用滑动相关和线性回归等方法,主要讨论了受ENSO影响的东亚冬季风分量和后期夏季风之间关系的年代际变化,并分析了二者关系发生变化的原因。结果表明:在1965—1979年,受ENSO影响的冬季风与后期夏季风强度的对应关系并不明显。在1980—2004年,受ENSO影响的冬季风强,对应后期的夏季风偏弱,弱冬季风对应的后期夏季风偏强。当受ENSO影响的冬季风较强时,冬季在对流层低层西北太平洋出现了异常气旋并可以维持到次年夏季,低纬地区位势高度偏低,削弱了西太平洋副热带高压,异常气旋西部的偏北气流阻碍了西南风的北进,导致夏季风偏弱。海表温度异常在1980年前后春、夏季不同的分布型可以解释环流在不同时段内的差异。

In terms of NCEP/NCAR reanalysis data, HadISST1 dataset and several representative monsoon indices, the interdecadal variation of the relationship between ENSO-related EAWM and the fol- lowing East Asian summer monsoon （EASM） was investigated by the methods of regression and moving- correlation. Moreover, the reasons of the variation were also analyzed. Results show that the negative rela- tionship is weak during 1965-1979,but became strong and statistically significant during 1980-2004. A strong ENSO-related EAWM led to negative geopotential height anomalies in middle-level and lower-level anomalous cyclonic circulation over the western North Pacific, which persisted from winter to summer and weakened the strength of West Pacific Subtropical High （WPSH） in summer during 1980-2004.Corre- sponding to the lower-level anomalous cyclonic circulation, the southwesterly of EASM was blocked by north wind in eastern China. Whereas the circulation anomalies of the above-mentioned quantities were weak during 1965-1979. The differences of sea surface temperature distribution in spring and summer be-tween two periods of time are possible reasons