赤道西太平洋-印度洋海温异常对亚洲夏季风的影响

本文采用了p-σ五层原始方程模式模拟并研究了赤道西太平洋-印度洋海温距平场对亚洲夏季风的影响,计算了四种不同的海温距平试验方案。试验结果表明赤道西太平洋海温正距平使对流层下层的印度低压明显加强,副高北挺,季风槽加深,同时加强了对流层上层的反气旋环流。赤道西印度洋暖海温的模拟结果与赤道西太平洋暖海温对上述系统的影响相反,而赤道西印度洋冷海温对季风环流的影响与赤道西太平洋暧海温的影响一致。试验进一步表明赤道西太平洋-印度洋海温距平的纬向梯度方向对亚洲夏季风的影响是主要的,这一结论与实际观测结果一致。本文进一步讨论了赤道海温距平对越赤道气流、印度洋赤道东-西纬向环流和非绝热加热场的影响,结果都表明赤道西太平洋海温正距平和赤道西印度洋海温负距平的模拟特征与反El Nino年亚洲夏季环流特征类似,而赤道西印度洋海员正距平的模拟特征与El Nino年亚洲夏季坏流特征类似。

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.