Submesoscale Processes Associated With the East India Coastal Current

Abstract Seasonal variations and generation mechanisms of the submesoscale features associated with the East India Coastal Current (EICC) are investigated using a high resolution (1 km) regional ocean model set up for the Bay of Bengal (BoB) during 2012–2013. Simulations show that EICC is extremely rich in submesoscale features manifested as fronts, filaments, and eddies and the associated submesoscale processes exhibit significant seasonal variations. Characteristics such as local Rossby number, normalized horizontal divergence, vertical velocity, and strain rate show marked increase during winter monsoon (November–January). Submesoscale features of EICC are least active during spring (March–April). EICC is much more active in the submesoscale regime than the open ocean. Frontogenesis is the strongest at the end of summer monsoon in the north bay and spreads throughout the EICC in winter monsoon. There is continuous conversion of available potential energy to kinetic energy throughout the year. In the summer monsoon, strong stratification caused by the increased freshwater influx from Ganga‐Brahmaputra rivers suppresses generation of mixed layer instabilities in the north bay. In the winter monsoon, freshwater advection by EICC enhances the generation of mixed layer instabilities. The Ertel potential vorticity is mostly negative for EICC region throughout the winter monsoon. Further investigations of the criteria for symmetric instability reveals that the conditions over EICC region remain highly susceptible to the symmetric instability throughout the winter monsoon. The seasonal variability and generation processes of submesoscale features of EICC are closely related to the seasonal variability of EICC and freshwater forcing of the bay.