Comparison of Model Fluxes with Surface and Top-of-the-Atmosphere Observations

The global observation network of the atmospheric broadband radiation reached an unprecedent extent in 1998 with the simultaneous availability of longwave and shortwave measurements of the Clouds and the Earth’s Radiant Energy System instrument on board the Tropical Rainfall Measuring Mission spacecraft, and of a number of surface stations as part of the Atmospheric Radiation Measurement, Baseline Surface Radiation Network, and Surface Radiation network programs. In this paper, these observations are used to assess the quality of the longwave and shortwave components of both the top-of-the-atmosphere and the surface radiation budget computed by the ECMWF operational forecast system. The main features of the boundary radiation are well captured by the system. Clouds appear to be the main modulator of the uncertainty of the top-of-the-atmosphere radiation and of the shortwave surface radiation. This is explained by both model cloud deficiencies and inadequate cloud representation in the radiative transfer schemes. The longwave surface radiation uncertainty is marked by a clear sky bias, common to most of the parameterized longwave radiative transfer models.