MEAN MONTHLY WIND-DRIVEN CLIMATOLOGICAL CIRCULATION MODEL OF THE BAY OF BENGAL

A special feature of the Bay of Bengal circulation is its seasonal var iation in response to the monsoonal winds. In the case of the Bay of B engal, observationally very little is known about the large scale circ ulation. Theoretically, the problem of driving the circulation in the Bay of Bengal is more complex than that in other basins because of the presence of large quantities of fresh water discharge from Ganga-Brah maputra-Meghna river systems, and also because the atmospheric driving forces even within a season are highly variable with frequent occurre nces of tropical disturbances. Exploring the nature of the circulation in the Bay of Bengal is a problem of great importance in itself as we ll as for the critical role this region plays in the genesis of tropic al disturbances which are the main source of large scale rainfall over the northern part of the Indian subcontinent. The surface circulation of the Bay of Bengal may, therefore, help in understanding the variat ion of rainfall over time scales ranging from the subseasonal to the i nterannual. Keeping this in view, an attempt was made towards the deve lopment of an oceanic climatological circulation model for the Bay of Bengal, which explains the seasonal variability of the currents. The m odel is fully non-linear and vertically integrated, with realistic bas in geometry. The treatment of coastal boundaries involves a procedure leading to a realistic curvilinear representation of the western and e astern sides of the Bay of Bengal. This coastal representation has the advantage of taking into account the finer resolution in the shallow regions of the northern Bay. The model is forced by the monthly mean w ind stress derived from 30 years (1950-79) of Comprehensive Oceanograp hic Atmospheric Data Sets (COADS). Special emphasis is given to the so uthern open boundary condition for the model. For this purpose, sensit ivity experiments have been performed with six open boundary condition s and a comparative study of the results has been made. These sensitiv ity tests for the open boundary condition will help the development of a suitable coupled ocean-atmosphere model for this region. The model- generated main features are in general agreement with the known climat ological circulation of the Bay of Bengal.