Mixing by semi-diurnal internal waves in the Bay of Bengal

Abstract:

Strong internal waves generated by tides found to propagate into the Bay of Bengal from their generation in the straits in Andaman Islands Archipelago. The waves has been observed in Synthetic Aperture Radar data, and appear as solitary wave packets. They are also present in subsurface temperature records from the RAMA mooring s. In this work the waves are simulated by a fully coupled ocean-atmosphere prediction system, exchanging surface fluxes between the air and sea at high frequency and high resolution. The ocean model includes diurnal and semi-diurnal tides and has a 2 km resolution in the entire Bay of Bengal. In the model simulations, large amplitude semi-diurnal internal waves interact with the meso-scale circulation and modify the flow and the stratification as far away as Sri Lanka. By comparing model runs with tides and without tides, but forced by identical surface fluxes from the atmosphere, we find that the inclusion of diurnal and semi-diurnal tides act to cool the thermocline due to vertical mixing. This imply that non-linear semi-diurnal internal waves may significantly contribute to mixing in the interior of the Bay of Bengal.