Mesoscale process-induced variation of theWest India Coastal Current during the winter monsoon

摘要

This manuscript presents the analysis of current meter records at Kollam and Kannur along the 20-m isobaths during November-December 2005. Currents in the coastal waters are strongly influenced by winds (both local and remote forcing), tides, propagation of coastal Kelvin and Rossby waves, etc. We hypothesize that the mesoscale (spatial scales of 10-500 km and temporal scale of 10-100 days) features in ocean are also competent to alter the characteristics of coastal currents to a large extent. Analysis of sea level anomaly from the merged altimeter data reveals the existence of a large anticyclonic eddy in the southeastern Arabian Sea during the winter monsoon. The eddy moves westward with an average speed of similar to 15 km day-1 corresponding to an increase in sea level amplitude up to 28 cm. Off southwest India, the poleward flow is along the western flank of this anticyclonic eddy and the geostrophic current completes the circulation around the eddy. The eastward component of the geostrophic current at the northern edge of the eddy is bifurcated at similar to 9 degrees N: one flowing towards north and the other towards south. Current meter records at station Kollam revealed a dominant southward current due to the bifurcated southward component. The bifurcated northward component coalesced with the poleward flow along the western flank of the anticyclonic eddy. At Kannur, a poleward flow along the coast is responsible for a predominant northward trend in the observed current pattern during the initial phase of observation. A reversal in the current direction is caused by the southward-flowing geostrophic current along the eastern flank of the subsequent anticyclonic eddy centered at 73.5 degrees E and 13 degrees N. The stations were located at the eastern periphery of these anticyclonic eddies, where the mesoscale features overwhelm the seasonal characteristics of the West India Coastal Current (WICC).