Dynamics of Eddy Generation in the Central Bay of Bengal

Eddy activity in the central Bay of Bengal (BoB) is revealed using satellite observations and hydrographic data. Altimetric data show that eddies are generated near the eastern boundary, propagate southwestward, and have periods predominantly in the 30- to 120-day band. Temperature profiles from the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) buoy at 90 degrees E, 15 degrees N, have their highest amplitude in the depth range of the thermocline, indicating that the eddies are associated with a vertical motion of the thermocline (a first-baroclinic-mode response). To investigate the cause of the eddies, we obtained a suite of solutions to nonlinear and linear versions of a 11/2-layer (reduced-gravity) model. They demonstrate that equatorial wind forcing, Myanmar bump and Andaman Island, and nonlinearity are all essential for eddy formation. Among the nonlinear terms, the advection terms are the primary cause. This study combines observations and model to understand eddy generation in the central Bay of Bengal. When equatorial wind-driven downwelling (upwelling) Kelvin waves propagate to the tip of the Irrawaddy Delta off Myanmar, anticyclonic (cyclonic) eddies are generated there that subsequently propagate southwestward. The eddies are mainly driven by equatorial zonal winds, with both nonlinearity and coastline geometry essential for eddy generation.