Dynamics of the East India coastal current 2. Numerical solutions

Abstract

A linear, continuously stratified model is used to investigate the dynamics of the East India Coastal Current (EICC). Solutions are found numerically in a basin that resembles the Indian Ocean basin north of 29°S, and they are forced by Hellerman and Rosenstein [1983] winds. Effects due to the following four forcing mechanisms are isolated: local alongshore winds adjacent to the east coasts of India and Sri Lanka, remote alongshore winds adjacent to the northern and eastern boundaries of the Bay, remotely forced signals propagating from the equator, and interior Ekman pumping. Each process contributes significantly to the EICC surface flow at some locations and at some times during the year. Along the Indian coast (north of 10°N), the surface EICC flows northeastward from February until September, with a strong peak in March-April and weaker flow from June to September; interior Ekman pumping, remote alongshore winds and equatorial forcing all contribute to the springtime peak, whereas local alongshore winds are the primary driving force of the weaker summertime flow. Along Sri Lanka (south of 10°N) the surface EICC flows northward only during March and April; the absence of northward flow at other times is due to interior Ekman pumping which drives a strong southward current for much of the year (April to December). Along both coasts there is southward flow from October to January that is driven by interior Ekman pumping and local alongshore winds. The EICC also has significant subsurface flow on several occasions. Along the Indian coast, there is southwestward flow extending to depths greater than 1000 m from May to July that is driven primarily by equatorial forcing. From July to September the southwestward flow forms a shallow subsurface counterflow (a Coastal Undercurrent); its cause is primarily equatorial forcing and interior Ekman pumping, not the local alongshore winds, as might be expected.