The eastern Arabian Sea (AS) shows marked seasonal changes in the current pattern, contrary to the eastern boundary currents of other oceans. The main aim of the study is to implement the Prienceton Ocean Model (POM) for the eastern AS to understand and interpret the surface and sub-surface processes of the region. The POM is adopted for the first time to the eastern part of AS using curvilinear orthogonal grids with a fine resolution nearer to the coast. The region of interest extends from 7N to 23.5 N with an offshore width of ~500 km covering the entire west coast of India.
The numerical simulations using climatological forcing fields show that during SW monsoon the southward current pattern is primarily dependent on prevailing wind pattern. Poleward flow during NE monsoon is mainly facilitated by the horizontal density gradient. The Kelvin wave further modifies the circulation by enhancing the northward flow very near to the coast. Also the formation of Lakshadweep High (LH) in Southeastern Arabian Sea (SEAS), during this period, becomes clearer with the inclusion of Kelvin wave effect. In chapter 4 the experiments are performed to understand the relation of LH and Lakshadweep Low (LL) in relation to temperature inversion and coastal upwelling in the SEAS during NE and SW monsoons respectively. The model is able to simulate observed LH and LL and their westward movement which is comparable with the climatological Sea Surface Height (SSH) derived from TOPEX data. Simulations also suggest that the TI in coastal waters increases from south to north during NE monsoon. This may be explained due to wintertime cooling in the north which enhances TI in the region whilst the presence of LH and its westward movement suppresses it in the south. The upwelling processes during SW monsoon are predominant in south as compared to the northern coastal regions. The upwelling fronts which are transient in nature also migrate westwards along with the LL.
The analysis of TMI SST shows that a Mini Cold Pool (MCP) observed near the southern Indian coastal region is strong in 1st week compared to that of 4th week. The model is able to simulate the MCP in the 1st week as a result of strong coastal upwelling using real-time forcing fields. The upwelling processes suppress in 4th week because of the reversed coastal currents generated as a result of weak wind pattern over the region. The intraannual variability of sea surface elevation and TI during December 2003 and 2004 are studied. The simulated elevation compares well with the observed trend of TOPEX SSH. The TI along the coast noticed in the mixed layer and is present above the layer of high saline AS water present at 50-60 m depth. The simulations also show formation of time-varying multiple eddies in the SEAS. It is noted that these are related to warm and cold core eddies.
Finally model’s performance during an extreme weather event like 1998 Kandla cyclone is seen. The computed maximum surface temperature cooling is about 4oC which compares qualitatively well with the observed SST data of TMI and buoy. The evolution of surface currents, elevation and vertical velocity generated by the passage of the cyclone are also studied. The simulated surge heights are in a reasonable agreement with the observations reported by the IMD. The SST and currents suggest that the return period of normalcy of the sea state is about 15 days after the cyclone crosses the coast. This is also confirmed with the satellite and buoy observations.