SEASONAL CYCLE OF TEMPERATURE AND ASSOCIATED WAVE PHENOMENA IN THE UPPER LAYERS OF THE BAY OF BENGAL

The seasonal cycle of temperature in the monthly mean Levitus (1982) data is analyzed by a least squares method fitting the observed temperature with a cosine function having a period of 1 year. It is found that the signal is most, pronounced in the subsurface levels (100-200 m), with high amplitudes in the western and eastern parts of the Bay of Bengal and low values in the central region. The peak of the seasonal cycle appears in the westernmost region during April, while in the easternmost region it appears during August. The amplitude of the seasonal cycle of temperature in the western and northern region is influenced by the local wind stress curl. From the values of phase obtained, wavelength and phase speed of annual wave are computed. At 100 m, the computed phase speed along 12.5 degrees N is 21 cm s(-1). According to theory (White, 1977), this annual wave, which is considered to be the sum of the effects of local wind stress and westward propagating Rossby waves, propagates westward with a phase speed equal to twice that of nondispersive Rossby waves. At 12.5 degrees N, the theoretical phase speed is 23 cm s(-1). There is a reasonable agreement between the computed and theoretical phase speeds at 17.5 degrees N also. From the depth of 20 degrees C isotherm along 12.5 degrees N and 17.5 degrees N, there are signatures of westward propagating Rossby waves. Along 12.5 degrees N, their phase speed is 8 cm s(-1), whereas the theoretical value is 11.5 cm s The signatures of northward propagation along the eastern periphery of the Bay of Bengal seen in the plots of the depth of 20 degrees C isotherm do not appear to be locally wind-driven.