Toward the Influence of Clouds on the Shortwave Radiation Budget of the Earth Atmosphere System Estimated from Satellite Data

Abstract

The purpose of this paper is to investigate the influence of cloudiness on the shortwave radiation budget at the top of the atmosphere, at the surface, and, as a residual, for the atmosphere itself. The data used for this study are derived exclusively from satellite measurements. Calculations for the top of the atmosphere are based entirely on measurements of the Earth Radiation Budget Experiment (ERBE). For the solar radiation budget at the surface, the incoming surface solar radiation is derived from Meteosat data and the surface albedo is calculated from ERBE clear-sky planetary albedo measurements by applying an atmospheric correction scheme. As results, maps of absorbed solar radiation for the total earth?atmosphere system, the surface, and for the atmosphere are presented for the area of investigation, ±60° longitude and latitude. To infer the contribution of clouds, the concept of cloud radiative forcing is applied to these different datasets. It is shown that the solar cloud forcing at the top of the atmosphere (CFTOA), and at the surface (CFSUR), are of the same order of magnitude and well correlated with cloud cover (R = 0.83). On the contrary, the solar cloud forcing of the atmosphere itself, CFATM, is about one order of magnitude less and not very highly correlated with cloud cover (R = 0.37). The mean value of the annual averaged solar cloud forcing for the area of investigation is calculated for the top of the atmosphere to be CFTOA = 50 ± 4 W m?2, for the surface to be CFSUR = 55 ± 6 W m?2, and for the atmosphere to be CFATM = ? 5 ± 10 W m?2. Related to the annual mean solar insulation, the CFATM corresponds to an additional contribution of the clouds to atmospheric solar absorption of 1.4%. The uncertainty range for this additional absorption is calculated to be ? 1.4% to + 4.2%.