71-76Diurnal scale variations observed in the vertical thermal structure at 3 stations of the continental shelf (off Cape Comorin, Vizhinjam and Cochin) during May 1985 are analysed with short time series data sets collected onboard R V Gaveshani (cruise 154). Heating and cooling cycles observed in the surface layer are qualitatively discussed in terms of surface heat exchange processes. Large amplitude variations noticed in the thermocline suggest the prominence of internal waves. Vertical eddy diffusivity coefficient evaluated at one of the stations showed a value of 72 cm2 sec-1
