Using an ocean model to validate ECMWF heat fluxes

Abstract

AbstractA general circulation model of the Indian Ocean has been used as one method of assessing the quality of surface heat fluxes over the ocean. The fluxes of momentum and heat obtained from the numerical‐weather‐prediction model of the European Centre for Medium‐range Weather Forecasts (ECMWF) for the period from 85 to 1988. The near‐surface temperatures simulated by the ocean model provide an indicator of the accuracy o these fluxes. From this study it was estimated that 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 model showed little similarity to those observed, however, raising the question about the quality for representing such processes and indicating a need for continued improvement.One potential improvement is in the parametrization of evaporation at low wind speed. The impact on the fluxes of such a change was investigated. The fluxes in this sensitivity study were also obtained from the ECMWF model, but from climate‐mode simulations rather than from analyses. The parametrization change was designed to raise the latent‐heat flux in areas of light winds, such as in the equatorial region. The ocean‐model intergration, however, suggest that the effect may have been overdone, with insufficient heat being put into the ocean. The change in evaporation not only changes the latent‐heat flux but also leads to substantial changes in the solar flux and in the surface wind and stress fields.