A note on poleward undercurrent along the southwest coast of India

Abstract

A comparative study of currents and hydrography during th monsoon and non-monsoon periods of 1984, 1985 and 1987 was carried out using data collected on five cruises covering the waters of the west coast of India from 8 degrees N to 15 degrees N and the inferences on upwelling and associated features are discussed. Climatological wind analysis indicate distinct behavioural variation between monsoon (May-September) and non-monsoon (November-March) periods. Between Cochin and Bhatkal the alongshore wind stress component builds up from May to reach a maximum during July and then decreases with time. Off Trivandrum the wind stress increases from 0.4 to 0.8 dynes cm sup(2). Wind driven surface currents are quite organised in the surface 75 m layer and are reversed at about 200m (depth of the 14 degrees C isotherm). Well defined thermal and saline fronts are visible adjacent to each other and close to the coastline with gradients of 0.06 degrees C km sup(-1) and 0.04ppt km sup(-1), respectively. Strong alongshore wind stress component is associated with maximum offshore transport and remarkable sea surface temperature anomaly. The strong surface wind drift weakens the poleward undercurrent during the monsoon period and as the undercurrent gains strength the surface drift is retarded. Penetration of very low salinity water mass (less than 33ppt) from the Bay of Bengal to the Arabian Sea during the non-monsoon period has also been observed.