孟加拉湾春季海温增暖对其夏季风爆发的影响

Influence of Sea Surface Temperature Warming in Spring on Monsoon Onset in Summer in the Bay of Bengal

孟加拉湾中部海表温度(SST)在春季快速升高,并在夏季风爆发前达到全年最大值。利用7a的卫星观测资料,进行合成分析,讨论孟加拉湾春季SST增暖对其夏季风爆发的可能影响。结果表明,SST增暖会通过诱导季节内振荡(ISO)进入孟加拉湾而影响夏季风爆发。春季,孟加拉湾中部SST的增暖引起大气底层水汽的快速上升从而显著增强局地的大气对流不稳定性,为对流的发展提供有利的背景条件。当ISO沿赤道传播至东印度洋时,对流加热引起的Rossby波响应,在南北半球产生2个涡旋(低压)扰动。位于孟加拉湾的Rossby涡旋扰动在对流不稳定的层结背景下发展成为强对流系统,其进一步向北移动从而触发孟加拉湾夏季风。

The sea surface temperature （SST） in the Bay of Bengal （BOB） increases rapidly in spring and reaches its maximum before summer monsoon onset. Base on satellite retrieval datasets obtained in 7 years and through a composite study, the influence of the SST warming in spring on the monsoon onset in sum- mer in BoB is discussed. The results indicate that the spring SST warming can influence the summer mon- soon onset by inducing the northward propagation of intra-seasonal oscillation （ISO） into BoB. In spring, the SST warming in the central part of BoB can lead to a rapid increase of surface moisture and hence enhances greatly the instability of local air convective in BoB, thus providing a favorable background for the convection. When the ISO travels to the Eastern Indian Ocean along the equator, disturbances of two gyres （low pressure centers） can be formed in both the southern and the northern hemispheres due to the Rossby-wave response caused by the convective heating. Under the background of convectively unstable stratification, the Rossby gyre disturbance in BoB develops to a strong convective system. This convection moves further northward, thus triggering the summer monsoon in BoB.