A short range pred iction of the onset phase of the southwest monsoon ( 1979)

Abstract

A global spectral model was used to predict the onset phase of the southwest monsoon -(1979). FGGE III-b and MONEX- 79 data sets were used as input. In the 5.day prediction experiment the strengthening of the monsoon westerlies along 5°N with maxima around 50°E and 70oE and the formation of the onset vortex on the poleward side of the monsoon current were in reasonable agreement with the observations. By for 5-day the vortex was correctly predicted to move north and form into a depression. The model output was examined to gain an insight into the physical mechanisms. The role of condensational heating in monsoon dynamics was found to be crucial. The adjustment processes between the evolving meridional pressure-gradient and zonal westerlies was traced in the point diagnostics of the model output at a point 5. O”N, 70°E situated in the monsoon jet. Energetics and vorticity computations 5howed that barotropic instability could not he the sole mechanism in the formation of the vortex in the model atmosphere.