Numerical modelling of tidally generated internal wave radiation from the Andaman Sea into the Bay of Bengal

Abstract

Semi-diurnal internal waves generated by tides in a high resolution numerical model that includes the Andaman Sea archipelago are found to propagate into the central Bay of Bengal and reach the coasts of India and Sri Lanka. The waves are also present in subsurface temperature records from RAMA moorings, and their propagation speed across the Bay of Bengal agrees well with satellite remote sensing from MODIS imagery in spite of the hydrostatic nature of the model. The internal waves are simulated by a fully coupled ocean-atmosphere prediction system, exchanging surface fluxes between the air and sea at high frequency and at high resolution. For the ocean, a hydrostatic model including diurnal and semi-diurnal tides provides a 2 km resolution representation of the entire Bay of Bengal. In the ocean model simulations, the semi-diurnal internal waves interact with the mesoscale circulation and surface waves and modify the flow and the stratification. By comparing coupled ocean-wave model runs with tides and without tides, but forced by identical surface fluxes from the atmosphere, it is demonstrated that the inclusion of diurnal and semi-diurnal tides act to cool the core of the thermocline while increasing the temperature above and below it along the pathway of the internal waves, a result that likely is due to vertical mixing by the waves.