Radiative Effects of Cloud-Type Variations

Abstract

Radiative flux changes induced by the occurrence of different cloud types are investigated using International Satellite Cloud Climatology Project cloud data and a refined radiative transfer model from National Aeronautics and Space Administration/Goddard Institute for Space Studies general circulation model. Cloud types are defined by their top height and optical thickness. Cloud-type variations are shown to be as important as cloud cover in modifying the radiation field of the earth?atmosphere system. Other variables, such as the solar insolation and atmospheric and surface properties, also play significant roles in determining regional cloud radiative effects. The largest ?annual? mean (approximated by averaging the results of four particular days, one from each season) changes of the global top-of-atmosphere and surface shortwave radiative fluxes are produced by stratocumulus, altostratus, and cirrostratus clouds (i.e., clouds with moderate optical thicknesses). Cirrus, cirrostratus, and deep convective clouds (i.e., the highest-level clouds) cause most of the annual mean changes in the global top-of-atmosphere longwave radiative fluxes; whereas the largest annual mean changes of the global surface longwave radiative fluxes are caused by stratocumulus, cumulus, and altostratus.