厄尔尼诺持续时间与大气环流异常形势

针对不同持续时间的El Nio事件，进行了大尺度大气环流及其演变的合成分析研究.其结果清楚地表明，不同持续时间的El Nio事件的发生、发展和消亡过程，对流层低层风场和对流层高层速度势场的距平都有极为显著差异.分析得到了对El Nio事件的发生和消亡起着重要作用的大气环流异常形势.还发现对于持续时间较长的El Nio事件，东北太平洋上850hPa异常气旋性环流减弱和西北太平洋上异常反气旋性环流增强较慢，因此赤道太平洋异常西风维持的时间也较长，而与澳大利亚冬季风加强相关联的南半球西太平洋的速度势正距平的维持，对El Nio的持续也起一定作用；对应持续时间较短的El Nio事件，西太平洋上200hPa速度势正距平的迅速东移，对El Nio的迅速消亡起重要作用.

Lasting time of El Ni(n)o and circulation anomaly

Composite circulation is studied for long lasting and short lasting El Nio events. The result shows that the low level wind and high level velocity potential anomalies are quite different in the occurring, developing and vanishing of the two El Nio events. The result also reveals the key anomalous circulation for the occurring and vanishing of El Nio. Corresponding to the long lasting El Nio event, cyclonic anomalous circulation over the eastern North Pacific weakens slowly and anticyclonic anomalous circulation over the western North Pacific strengthens slowly at 850 hPa. Therefore the tropical Pacific westerly anomaly keeps long. The anomalous positive velocity potential over the western South Pacific at 200 hPa, which is related to the strong Australian winter monsoon, helps a long duration of El Nio. Corresponding to the short lasting El Nio, the anomalous positive velocity potential over the western Pacific at 200 hPa moves eastward quickly and results in the vanishing of El Nio event.