Another Look at the Influence of Absorbing Aerosols in Drops on Cloud Absorption: Large Aerosols

Abstract

Since as early as 1969, solar absorbing aerosols inside of cloud drops have been suggested to influence cloud radiative properties. The absorbing aerosols were invoked to help explain two ?anomalies?: 1) the maximum visible albedo of thick stratocumulus clouds is observed to be only 0.7?0.8, rather than close to 1.0 as would be expected from pure water clouds, and 2) the total solar cloud forcing ratio is observed to be near 1.5 for a wide range of clouds, rather than near 1.0 as would be expected from pure water clouds. While subsequent studies refuting absorbing aerosols have been limited to certain aerosol and cloud drop size ranges, in this study the authors explore the potential radiative effects of supermicron dust and soot aerosols in cloud drops, which can have especially high absorption cross sections. Because of the lack of measurements and limited microphysical simulations of such supermicron absorbing aerosols, it is not suggested that the calculations will entirely resolve the two anomalies. However, because these aerosols certainly can exist in the vicinity of clouds, the authors suggest that their potential contribution to the understanding of the anomalies should be explored. This study serves as an initial step toward that goal.