Interactions among deep convection, sea surface temperature and radiation in the Asian monsoon region

Abstract

The climatic interactions among deep convection, sea surface temperature and radiation in the Asian monsoon region have been examined using various satellite-derived data sets of the period 1983-90. Annual average Frequency of Deep Convection (FDC) was maximum over the equatorial east Indian Ocean and adjoining West Pacific and Indonesian Region. Maximum FDC zone shifts to Bay of Bengal during the monsoon (June-September) season. There was a weak relationship between the variations in FDC and SST in the Indian Ocean. Deep convective activity was suppressed over most of the tropical Indian Ocean during El Nino of 1987 in spite of warmer SSTs. The pattern of interannual variation between FDC and SST behaves differently in the Indian Ocean basin as compared to the Pacific net negative cloud radiative forcing. Variation in FDC explains more than 70% of the variation in surface shortwave cloud radiative forcing (SWCRF) and long wave cloud radiative forcing (LWCRF) in the atmosphere. On inter-annual scale, warmer SSTs may not necessarily increase deep convection in the Indian Ocean. However, the interannual variation of deep convective clouds influences significantly the radiative budget of the surface-atmosphere system in the Asian monsoon region. The satellite observations suggested that warmer SSTs in the Indian Ocean might have resulted from an increase in the absorbed solar radiation at the surface due to a reduction in deep convective cloud cover.