database for fast radiative transfer model

ABSTRACTTo assimilate the sateffite informations, meteorological forecasting models need, at each iteration, an accurate radiativetransfer model. This model must be very fast and line by line models are inadequate.So much faster models, adapted to pre-defined filters, have been developped.Meteo-France has choosen the fast Radiative Transfer for Advanced Tiros Operational Vertical sounder (RTATOV)1 model developped at the European Centre for Medium-Range Weather Forecasts (ECMWF). It uses at each working pressure level, 3 independant polynomial modeisations with non4inear terms as functions of temperature, specific humidityand ozone from the input atmospheric profile. The coefficients of the polynomial equations are off-line calculated by linear regression on atmospheric transinittances. For each new satellite, the regressed coefficients have to be recomputed. The purpose ofthis study is to develop the tools for quickly calculating these coefficients. To avoid the problem of large computing time inherent in line-by-line calculations, we have generated a database of