Impact of Indian Ocean warming on increasing trend in pre-monsoon rainfall and Hadley circulation over Bay of Bengal

Abstract

In the present manuscript, we analyzed the pre-monsoon (March–April–May) rainfall over the Indian summer monsoon region using the Global Precipitation Climatology Project (GPCP) rainfall datasets during 1979–2015. It is found that the rainfall over the Bay of Bengal (BOB) has increased significantly and it is associated with the strengthening of local Hadley circulation over the BOB. The increasing Sea Surface Temperature (SST) over the Indian Ocean is playing an important role to the observed changes in convections and cloudiness over the BOB. In addition, the strengthening of the westerly enhances the wind speed and transports more moisture to the North Indian Ocean. In addition, warming of the SST and large-scale moisture convergence cause the rainfall to increase and the latent heat released in the process strengthens the divergent wind at 200 hPa. This strengthens the local Hadley circulation over the BOB, which may affect the monsoon strength over the Indian subcontinent, by influencing the onset of the Indian summer monsoon. This study will improve the understanding by monitoring the changes in the atmospheric processes over the BOB and the Indian subcontinent, which may result in better predictability of the Indian summer monsoon.