Optimized Surface Radiation Fields Derived from Meteosat Imagery and a Regional Atmospheric Model

Abstract

High-quality fields of surface radiation fluxes are required for the development of Land Data Assimilation Systems. A fast offline integration scheme was developed to modify NWP model cloud fields based on Meteosat visible and infrared observations. From the updated cloud fields, downward shortwave and longwave radiation at the surface are computed using the NWP radiative transfer model. A dataset of 15 months covering Europe was produced and validated against measurements of ground stations on a daily basis. In situ measurements are available for 30 stations in the Netherlands and two Baseline Surface Radiation Network (BSRN) stations in Germany and France. The accuracy of shortwave surface radiation is increased when the integration system is applied. The rms error in the model forecast is found to be 32 and 42 W m?2 for the period from October 1999 to December 2000 for the two BSRN stations. These values are reduced to 21 and 25 W m?2 through the application of the integration scheme. During the summer months the errors are generally larger than in winter. Because of an integrated monitoring of surface albedo, the performance of the scheme is not affected by snow cover. The errors in the longwave radiation field of the original NWP model are already small. However, they are slightly reduced by applying the integration scheme.