AN APPLICATION OF A WIND-DRIVEN COASTAL UPWELLING MODEL IN THE WESTERN BAY OF BENGAL

A three-dimensional numerical model of the type described by JOHNS et al. [Quarterly Journal of the Royal Meteorological Society, 109, 211-224 (1983)] and further developed by LI (unpublished thesis, 1989) is applied to study the response to local wind-stress forcing of the coastal ocean in the western Bay of Bengal. Limited data on the thermal structure of the ocean off Visakhapatnam are utilized in an attempt to determine whether the observed form of the isotherms may be positively identified as a response to the pattern of local pre-monsoon and monsoon wind-stress forcing associated with periods of south-westerly and north-easterly winds prevailing during the months of March and October. Comparison of the model results with the observational data appears to support such an identification and an account is given of the corresponding computed currents to ascertain both the qualitative and quantitative form of the circulation responsible for the support of the observed thermal pattern. It is shown that south-westerly and north-easterly wind-stress forcing lead, respectively, to circulation patterns characteristic of those to be expected in classic Ekman-divergence-induced upwelling and downwelling processes. Thus, it is positively demonstrated that the changes in the sea-surface temperature and the upwarping and downwarping of the isopycnals observed by RAO et al. (1986) during the months of March and October may be explained in terms of upwelling and downwelling induced by the local winds prevailing during those periods.