Coupled atmosphere-ocean modeling in the presence of shallow barrier layers in the Bay of Bengal

The Arabian Sea has high salinity due to more evaporation than rainfall while the Bay of Bengal has much lower salinity due to large fresh-water fluxes from high rainfall and river discharge. A shallow fresh water plume flows down the Indian coast and then around Sri Lanka. Modeling of this rapid and shallow low-salinity surface flow, the strong diurnal cycle in sea surface temperature and surface heat fluxes is challenging because of the high vertical resolution required in the upper ocean.

A fully coupled atmosphere-ocean wave model (COAMPS-NCOM-SWAN) is used, covering the western Arabian Sea, India and the Bay of Bengal to the equator. The atmosphere model uses three nested grids: 18-km, 6-km and 2 km resolution and 50 vertical levels. The ocean model has a horizontal resolution of 1/24^o for with 60 vertical levels that provide a vertical resolution of 0.5 m in the upper 10 m. The wave model has a spatial resolution of 1/8^o with 33 frequency bands and 48 wave directions. The coupled models are used to investigate the variability of mesoscale processes on weekly time scales with emphasis on the impact of local rainfall on the diurnal cycle of heat flux, advection of low salinity water and the impact on the mixed layer depth and formation of barrier layers in the ocean.