Impact of Bay of Bengal mesoscale eddies on Indian Summer Monsoon Rainfall

The northern Indian Ocean serves as an ideal space to study the interaction between Ocean and atmosphere as it accommodates unique and versatile oceanic conditions and the largest monsoonal circulation in the world. The South Asian Monsoon System, the largest of its kind, directly impacts the lives and livelihoods of billions of people living in the Indian Subcontinent. Various factors that influence its strength and characteristics have been studied extensively throughout the years. But, owing to its complex and dynamic nature, a comprehensive understanding and accurate monsoon prediction remain a work in progress. Several Oceanic components that play a part in monsoon processes have been identified. Our study focuses on the Bay of Bengal, distinguished from other oceans due to its highly stratified upper layers. Through this study, we aim to understand the Impact of mesoscale eddies in the Bay of Bengal on the Indian Summer monsoon.

 

The influence of oceanic mesoscale eddies on the circulation and precipitation directly over them has been addressed through different studies after the advent of high-resolution satellite data. The current research focuses on the large-scale influence of the eddies in the Bay of Bengal on the seasonal rainfall during the Indian summer monsoon(ISM). Indices were created using the Okubo Weiss parameter to understand the inter-annual variation of eddies (classified according to polarities and regions of occurrence). These indices correlated with the ISM system suggested that Anticyclonic eddies in the  Western Bay of Bengal strongly influenced wind and rainfall patterns over the monsoon region. The Anticyclonic Eddy activity that peaked during the El Nino years countered the suppression of rainfall by El Nino through enhanced synoptic activity in BoB. The low-pressure system formation and propagation in BoB were found to be stronger in the years having more anticyclonic eddies. The warming created by the warm-core Anticyclonic eddies initiates an Anticyclonic(Clockwise) circulation around the region, which feeds back into the existing oceanic conditions. This coupled Ocean-Atmospheric system mediated through the mesoscale eddies needs to be further analyzed through stand-alone and coupled modeling experiments. Improving the representation of the mesoscale processes in the Northern Indian Ocean can serve as a crucial step in improving the monsoon prediction systems.