EAST ASIAN MONSOON INDEX AND ITS INTER-ANNUAL RELATIONSHIP WITH LARGESCA-LE THERMAL DYNAMIC CIRCULATION

A new East Asian monsoon index is developed for land-sea between zonal and meridional thermal difference in terms of East Asian zonal sea-level pressure contrast combined with high and low-level zonal wind shear at low latitudes.The index-shown seasonal and interannual variation of summer monso n goes well with the western Pacific subtropical high (WPSH) ridge and better reflect the drought/flood in the middle-low reaches of Yangtze river.Results show that the summer monsoon bears significant anti-correlation relationship with the anti-Walker circulation over Indian and western Pacific oceans and the cross-equatorial monso on circulation in Asia.The convergence and divergence center of anomalous Walker circulation over western Pacific ocean at low and high level is not vertical superimposed in stronger and weaker summer monsoon year.The pronounced correlation region between velocity potential at 200hPa level and summer monsoon index is over western North Pacific,thereby the anomalous zonal circulation can affect the WPSH at 500 hPa by virtue of its convergence anomaly.The Walker circulation coupled with SSTA exhibis a meridional asymmetrical character over Australian and Asian monsoon regions on the basis of SVD,there exists directly connection between East Asian monsoon and air-sea interaction in the framework of such circulation.