Evaluating the Seasonal Variations of the Indirect Effect of Sulfate Aerosols Using Observation-Derived Cloud Climatology

We evaluate the "indirect," i.e., cloud-induced, shortwave effect of anthropogenic sulfate aerosols in marine stratocumulus clouds. The latter have a pronounced climatic effect due to their high reflectivity compared to the sea surface, large global coverage, and near-absence of greenhouse effects. The indirect effect is thought to be less pronounced in continental clouds, in part because these clouds evolve in more abundant cloud condensation nuclei (CCN) environments and, therefore, are less susceptible to the aerosol augmentation, and in part because the reflectivity of deep convective clouds and storms which prevail over land is less affected by the anthropogenic aerosol changes confined mostly to the boundary layer.