Forcing mechanisms of the Bay of Bengal circulation

Abstract

A state-of-the-art ocean general circulation model, set up for the North Indian Ocean and driven by climatological wind stress simulates most of the observed features of the near-surface circulation of the Bay of Bengal. The prominent features of the annual cycle are an anticyclonic gyre with a poleward East India Coastal Current (EICC) during February-May, and an equatorward EICC during October-December. During the summer monsoon, the coastal current flows poleward in the south and equatorward in the north. To identify the principal mechanisms governing this cycle, we carried out experiments with modified winds. When spatially uniform wind stress was applied only over the Bay, the circulation is similar to, but weaker than the observed, and can be linked to two coastal Kelvin wave pulses which originate along the eastern boundary of the Bay during the summer and winter monsoons. When the Bay is forced with observed winds, the wind stress curl strengthens the poleward EICC during February-May and the equatorward EICC during October-December. The principal contribution of equatorial winds is to generate the equatorward coastal current during the summer monsoon off the east coast of India.