A three-dimensional numerical model of coastal upwelling along the west coast of India

A three-dimensional baroclinic numerical model is developed and used to study the response of a coastal ocean to mean monthly pure wind-stress forcing representative of northeast monsoon and different phases of the southwest monsoon along the west coast of India. The model incorporates coastal ocean physics as realistically as possible by resolving surface and bottom Ekman layers. Conservation equations are applied for mass, momentum, thermal energy, salinity and turbulent energy. The governing equations together with their boundary conditions are solved by finite-difference techniques. Experiments are performed to investigate the thermal response and associated alongshore currents of the coastal waters in the southeast Arabian Sea using monthly mean wind-stress forcing. The model simulations suggest that the upwelling process is initiated during pre-monsoon month of May along the coastal waters off the extreme southwest peninsular region. The upwelling is more intense when the monsoon is at its peak in July compared to May and September and the associated reduction of SST increases towards south in the coastal waters as a result of pure wind-stress forcing. During northeast monsoon season, which is represented in the model by the January wind stress forcing, the model simulations indicate that the wind forcing does not favour upwelling. The relationship between coastal upwelling and longshore currents is also studied. The model predictions of coastal circulation, alongshore current and vertical temperature structure at selected stations are compared with the limited observations available.