Thermal structure of the Western Indian Ocean during the southwest monsoon, 1983

Abstract

The thermal structure and the variability of heat content of the upper 400 m of the Western Indian Ocean were examined using the expendable bathythermograph (XBT) data collected onboard RV Sagar Kanya during July-August, 1983. Vertical displacement of the thermocline was found to be closely associated with the spatial changes in the heat content integrated to 300 m depth. Besides, the low heat content in the study region near the land boundaries was also due to the coastal upwelling along India and Somalia. The south central Arabian Sea appeared to be a warm region with higher heat content, while the cold regions were located essentially along the coasts of Somalia and India. In the south central Arabian Sea the heat was tansferred vertically downwards from the surface and resulted in increasing the heat content of the subsurface layers as far as 300 m depth. A warm eddy was also seen adjacent to the cold eddy towards the Somalian coast in the 0-300 m layer. This, however, was missing in the 0-400 m layer. A poleward propagating upwelling front was located off the west coast of India. Large horizontal and vertical gradients of temperature in the subsurface were associated with the eddies at the surface. A weak thermocline spreading was observed around the equator between 3 degrees N and 1 degrees N and 1 degrees S along all the cross-equatorial sections. Though this was associated with an eastward flow, it is not as strong as the equatorial undercurrent that normally occurs during the winter and spring seasons. This feature, however, was consistently present around 100 m depth and showed a gradual southward shift in an easterly direction