Seasonal variability of the temperature field off the South-West coast of India

Abstract

The temperature field in the coastal region off south-west India exhibits a wellmarked annual cycle. Around March the isotherms develop an upward tilt near the coast. The magnitude of the tilt increases continuously till August, then decreases and vanishes in November. To check the hypothesis that this feature is in response to the local wind, we have used the resultant wind data to determine the annual march of the wind stress. It is found that though weak during November-March, the monthly-mean longshore component of the wind stress is always conducive to coastal upwelling and follows a pattern similar to that of the isotherm tilt. We interpret this result to indicate that coastal processes in the area during April-October are controlled by the longshore component of the local wind stress in accordance with the classical model for a coastal upwelling system. During November-March, when the wind stress is weak, it appears that the influence of the longshore density gradient, which persists at the surface during this period, dominates over the effect of the wind.