ON THE IMPACT OF DIVERGENT PART OF THE WIND COMPUTED FROM INSAT OLR DATA ON GLOBAL ANALYSIS AND FORECAST FIELDS

In this paper, a procedure for the computation of the divergent part o f wind from Outgoing Longwave Radiation (OLR) data is described. This divergent part is included in the global analysis scheme and its impac t is studied by computing the vertical velocity, velocity potential et c., using the analysed fields with and without modifying the divergent part and also making 24 hr and 48 hr rainfall forecasts. Results show that magnitudes of vertical velocity were increased when the divergen t part was modified in the wind analysis. There were also changes obse rved in the analysed wind field over convective regions and the change s over the oceanic regions were higher, suggesting that the impact of divergent part is more pronounced over data sparse regions. Marginal i ncrease was observed in 24 hr and 48 hr rainfall forecast over the Ind ian region. The area averaged rainfall forecast at each time step in t he first 6 hours of model integration was also higher in the case when the wind field contained the divergent part. To sum up, it can be sta ted that the inclusion of the divergent part from OLR data in the init ial wind field has brought out positive impact on the wind analyses an d rainfall forecast.