Impacts of Intraseasonal SST Anomalies on Precipitation during Indian Summer Monsoon

The forcing and response relation between the ocean and the atmosphere is often a two-way street. Based on the correlation between the surface heat flux and sea surface temperature (SST), it is found that the ocean plays an active role during the Indian summer monsoon (ISM) in two regions: one is the western coast of the Indian peninsula (WCI) and the other is the northern Bay of Bengal (NBB). A focus is made on the impacts of intraseasonal oceanic variabilities on heavy precipitation in these two regions during the ISM. Results show that warm intraseasonal SST anomalies contribute to the instabilities and deep convection in the atmosphere. In WCI, static instability is largely responsible for triggering convection, while in NBB, convection is mainly attributable to baroclinic instability. Despite such regional differences in instability mechanisms, heavy precipitation events during the ISM usually occur within ~3-6 days after the warm SST anomalies are organized. Understanding this process will be helpful to improve the predictive skill of the intraseasonal variabilities during the ISM, which is the lifeline for the countries on the rim of the Indian Ocean, whose food production depends critically on this seasonal phenomenon.