Variability of coastal ocean processes along the west coast of India

Three-dimensional Princeton Ocean Model (POM) is used to understand coastal ocean processes and its variability along the west coast of India. An attempt is first made to understand variability of the surface circulation and associated SST during July-August 2000 and 2002 as a response of daily wind stress forcing derived from the QSCAT winds. The coastal current reverses its direction to either off-shore or northward if the wind reduces its strength suddenly to less than 3 ms towards the coast. In this event, the coastal upwelling is inhibited by the reversal of near shore currents and results in an increase in the local SST. This feature is also noticed in the buoy data available for 2002. Another experiment is made to understand the dynamics in relation to the fact of observed low-salinity plume off Gulf of Khambhat during post-monsoon season. It is found that the freshwater discharge to the gulf from the adjoining rivers during monsoon season is trapped in the region as the currents are onshore. As the currents change its direction to offshore after withdrawal of the monsoon, the confined low-salinity waters are being released to the open ocean. Lastly, the study is made to understand the response of the ocean to tropical cyclones in the Arabian Sea (AS). The study focuses on surface cooling and temperature rise in the subsurface waters and explained its mechanism through upwelling and downwelling processes respectively. Local stratification of the vertical temperature plays an important role for the cooling of the surface waters and warming in the sub-surface depths. The analysis of the model simulations and observations suggest that the extent of sub-surface warming is directly related to the depth of the thermocline region.