Effect of precipitation on the albedo susceptibility
of clouds in the marine boundary layer
Robert Pincus and Marcia
B. Baker
Nature, 17 November 1994
Volume 372, pages 250-252.
doi:10.1038/372250a0
Abstract
Tropospheric aerosols are thought to have three major effects on the Earth's radiation budget: the direct effect (i.e. perturbation of clear sky reflectivity), the indirect effect (modification of cloud albedo), and the effect on the hydrologic cycle (modification of cloud thickness and horizontal extent). The first two effects have been understood in principle for nearly twenty years and quantitative estimates of their magnitudes have been provided by models and observations. The third phenomenon, and its relation to the other two, has received far less attention. Previous work has shown, however, that increases in aerosol concentration may act to increase cloud albedo by increasing horizontal cloud fraction as well as cloud reflectivity. Here we use a simple model of the marine cloud-topped boundary layer to investigate the changes in cloud thickness and albedo which results from changes in precipitation as particle concentrations vary. We find that the sensitivity of cloud albedo to droplet number concentration (the "albedo susceptibility") is increased by 50-200% when the dependence of cloud thickness on particle number is included. The results suggest that treatment of the response of cloud thickness to changes in aerosol particle concentration will be necessary for accurate prediction of global albedo by climate models.