USING AN OCEAN MODEL TO VALIDATE ECMWF HEAT FLUXES

A general circulation model of the Indian Ocean has been used as one m ethod of assessing the quality of surface heat fluxes over the ocean. The fluxes of momentum and heat were obtained from the numerical-weath er-prediction model of the European Centre for Medium-range Weather Fo recasts (ECMWF) for the period from 1985 to 1988. The near-surface tem peratures simulated by the ocean model provide an indicator of the acc uracy of these fluxes. From this study it was estimated that the bias in the net surface heat flux in the annual average was better than 20 W m-2, though this could shroud larger errors in shorter averages. The interannual differences in sea surface temperature simulated by the m odel showed little similarity to those observed, however, raising the question about the quality of the fluxes for representing such process es and indicating a need for continued improvement. One potential impr ovement is in the parametrization of evaporation at low wind speed. Th e impact on the fluxes of such a change was investigated. The fluxes i n this sensitivity study were also obtained from the ECMWF model, but from climate-mode simulations rather than from analyses. The parametri zation change was designed to raise the latent-heat flux in areas of l ight winds, such as in the equatorial region. The ocean-model integrat ions, however,suggest that the effect may have been overdone, with ins ufficient heat being put into the ocean. The change in evaporation not only changes the latent-heat flux but also leads to substantial chang es in the solar flux and in the surface wind and stress fields.