On the radiation budget in regional climate simulations for West Africa

Abstract

This paper discusses the simulated monthly radiation budget of West Africa by eight regional climate models and the impact of three uncertainty sources in the simulations: cloud fraction, surface albedo, and surface temperature. The models were driven by the European Centre for Medium‐Range Weather Forecasts ERA‐Interim reanalysis data within the European Union project ENSEMBLES. The simulated budgets were compared to the satellite‐based Global Energy and Water Cycle Experiment Surface Radiation Budget and ERA‐Interim data sets. The simulations tended to underestimate the net solar radiation and the outgoing long‐wave radiation, and they showed a regionally varying over‐ or underestimation in all budget components (up to 75%). The evaluation showed that uncertainty in the cloud fraction is the most important of the uncertainty sources over the ocean (with explained error variances between 25% and 60% depending on the budget component averaged over all models). Over land, the surface albedo and surface temperature were, on average, of similar importance as the cloud fraction. The latter result differed from that in a recent study for Europe, indicating that the importance of land surface on the radiation budget is regionally dependent. The relatively simple factor of surface albedo still explains a substantial part of the solar budget error variance in this study: more than 10% over ocean and more than 20% over land, peaking to more than 60% over the Sahelian and Saharan areas. It is worth improving on that in the models, in view of the complexity of other factors like cloud inhomogeneity and direct and indirect aerosol effects.