Interannual Variations in Asian Summer Rainfall and Their Associations with Tropical Convective Activities and Global SST Anomalies

Abstract

Interannual variations of summer rainfall over Asia and their associations with geopotential heights in the Northern Hemisphere, tropical convective activities and global sea surface temperature (SST) anomalies are investigated. The Empirical Orthogonal Function (EOF) analysis is applied to the summer rainfall data (JJAS) at 220 stations from 1951 to 1991 in order to reveal the spatial structure and its temporal evolution in the interannual variation of summer rainfall over the Asian region including from India to East Asia. The EOF 1 is detected as the component associated with the Warm Event of ENSO. In other words, the spatial pattern and its time coefficients of EOF 1 indicate that the amount of precipitation decreases over India and the north of China in El Nina years. The EOF 2 has a spatial structure with the same sign from India to East Asia; in particular accompanied with large signals in the middle latitude of East Asia. The variations of these EOFs are connected with those of tropical convective activities and SST anomalies. The variation of EOF 1 is suggested to be associated with the movement of heat source from southeastern Tibet to the southwestern part of China from the correlation coefficients pattern both for the geopotential height fields and the OLR. On the other hand, the EOF 2 is related to variations of convective activities extending from the north of the Philippines to the eastward along 15°N, which are accompanied by negative correlation coefficients to the variation of SST anomalies from the South China Sea to the eastern equatorial Indian Ocean.