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Using a global spectral model with wave-CISK formulation we have generated an eastward de which. Resembles the observed 30-50 day mode. This has a scale of global wave number one and two years structure in the vertical. It has the structure of a composite of Kelvin and Rossby waves. This composite  system moves eastwards. We have also studied a linear two-level analytical model to understand the nonlinear spectral model response. In the linear as well as in the nonlinear spectral model, as we Increase the moisture availability factor the speeds of the waves decrease. In the linear model this speed is found to be independent of drag for all types of waves. In the nonlinear spectral model for a given drag there is a critical value of the moisture availability factor for which the wave becomes stationary and beyond which even shows westward propagation. Thus both moisture availability and nonlinearity appear to contribute to the slow eastward speed of the equatorial 30-50 day mode.

Using an airborne scanning IR-radiometer, measurements of sea surface temperature (SST) were made from nine different levels in the Sandheads region of the Bay of Bengal on 5 October 1978. To retrieve SST from the observed radiances a temperature correction scheme, which uses the radiosonde data in the vicinity of flight area, has been generated. Atmospheric effects which have been considered include absorption due to water vapour and carbon dioxide, and the re-emission from different atmospheric layers. The radiances observed at different altitudes when corrected by our scheme yield a fairly consistent value of SST. The special ship measurements of SST, at the same location, are found to have very good agreement with the SST retrieved from the observed radiances using our scheme. The temperature corrections turn out to be 0" 3 and 3.3 ~ C at 600 and 3000 meters respectively for the type of atmosphere which has been used in our study.