ABSORPTION OF SOLAR-RADIATION BY CLOUDS - INTERPRETATIONS OF SATELLITE, SURFACE, AND AIRCRAFT MEASUREMENTS

To investigate the absorption of shortwave radiation by clouds, we hav e collocated satellite and surface measurements of shortwave radiation at several locations. Considerable effort has been directed toward un derstanding and minimizing sampling errors caused by the satellite mea surements being instantaneous and over a grid that is much larger than the field of view of an upward facing surface pyranometer. The colloc ated data indicate that clouds absorb considerably more shortwave radi ation than is predicted by theoretical models. This is consistent with the finding from both satellite and aircraft measurements that observ ed clouds are darker than model clouds. In the limit of thick clouds, observed top-of-the-atmosphere albedos do not exceed a value of 0.7, w hereas in models the maximum albedo can be 0.8.