Absorption of solar energy in cloudless and cloudy atmospheres over Germany and in GCMs

Clear-sky and all-sky shortwave atmospheric absorption in several General C irculation Models (GCM) is assessed using observational data from selected sites in Germany. Estimates of shortwave absorption in the atmosphere are o btained by combining surface clear-sky and all-sky climatologies derived fr om the ground observations with collocated top of atmosphere (TOA) clear-sk y and all-sky fluxes from the Earth Radiation Budget Experiment (ERBE). It is shown that the atmospheric absorption in the cloud-free atmosphere is on average 12 Wm(-2) too low in the GCMs. GCMs which include state-of-the-art radiation schemes and aerosol effects may be able to eliminate a large par t of this clear-sky bias. The model-calculated absorption in the cloudy (al l-sky) atmosphere is generally not significantly enhanced compared to the c loud-free atmosphere. This is in line with the observational estimates whic h are similar under all-sky and clear-sky conditions, indicating that the p resence of clouds does not substantially alter the absorption of solar radi ation within the atmospheric column. The observations therefore do not supp ort recent arguments that clouds in GCMs absorb insufficient solar radiatio n.