The use of TOVS clear radiances for numerical weather prediction using an updated forward model

The impact of TOVS clear radiances, processed using a new transmittance database, on the ECMWF forecast system, is evaluated. This involved the production of a line‐by‐line transmittance database, of sets of coefficients for the operational fast radiative‐transfer scheme, and the use of the operational bias‐correction procedure to reduce residual long‐term systematic differences. Two case‐studies are used to examine data from TOVS instruments on three NOAA satellites, and the differences in radiances measured by the various platforms are discussed. Measured and simulated data are compared before and after the operational bias‐removal scheme, and a final impact assessment is made using an assimilation and forecast experiment.