THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE EQUATORIAL WESTERN PACIFIC AND THE INDIAN OCEAN ON THE ASIAN SUMMER MONSOON

In this paper, the p-Q five layer primitive equation model is used to investigate the effects of sea surface temperature anomalies over the equatorial Western Pacific and the Indian Ocean on the Asian summer monsoon and to examine four sets of numerical experiments with different distribution of sea surface temperature anomalies. The experimental results show that the Indian low in the lower tropsphere and the anti-cyclone in the upper troposphere over the south Asia is intensified, the subtropical high moved northward and the monsoonal trough deepened when postive SST anomalies ovar tie equatorial Western Pacific is inserted. The simulated results with warmer spa surface temperature over the equatorial Westrn Indian Ocean is opposite to that with warmer sea surface temperature over the equatorial Western Pacific.However, the effects of cold SST over the equatorial Western Indian Ocean on the summer monsoon is consistent with that of warm SST over the equatorial Western Pacific. The experiments further indicate that zonal gradient direction of SST anomalies over the equatorial Western Pacific-Indian Ocean has an important influence on the Asian summer monsoon, which is in agreement with observation. Furthermore, the effects of equatorial SST anomalies on the cross equatorial flow, the equatorial east-west zonal circulation over the Indian Ocean and the diabatic heating field are also discussed. Obviously, characteristics of the circulation simulated by the model with positive SST anomalies over the equatorial Western Pacific or negative SST anomalies or over the equatorial Western Indian Ocean are similar to that of the observed summer circulation over the Asia during, an anti-El Nino year. whereas the simulated characteristics by the model with positive SST anomalies over the equatorial Western. Indian Ocean are consistent with the observed circulation during an El Nino year.