Tropical Convection and the Energy Balance at the Top of the Atmosphere

Abstract

Earth Radiation Budget Experiment (ERBE) and International Satellite Cloud Climatology Project (ISCCP) data are used in conjunction with a radiative transfer model to estimate the effect of various cloud types on the top-of-atmosphere radiation budget in convective regions of the Tropics. This analysis shows that individual convective cloud elements can have strongly positive or negative effects on the radiation balance. Nonetheless, the ensemble of cloud types that occurs in association with deep convection in the Tropics arranges itself so that the individual positive and negative contributions cancel each other when averaged over the convective cloud system. This behavior of the cloud ensemble is extremely interesting, and the authors speculate that it is indicative of feedbacks in the climate system that have not been explored adequately. A simple model is introduced that includes feedbacks that drive the net radiation in convective regions toward the net radiation in adjacent nonconvective areas. If the nonconvective regions have small cloud forcing, then this model predicts small net radiative forcing by the convective cloud ensemble. This feedback process requires that the circulations in the Tropics be sensitive to small SST gradients and that the convective cloud albedo be sensitive to the vertical motion.