Cloud Type Radiative Effects from the International Satellite Cloud Climatology Project

The cloud type radiative effects on individual radiative flux components are defined by the difference between the flux calculated with and without clouds present with all other (surface and atmospheric) quantities held fixed, and are estimated using ISCCP cloud data and a refined radiative transfer model from GISS GCM. 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, atmospheric and surface properties, also play significant roles in determining regional cloud radiative effects.

With a uniform mix of cloud types, the three cloud types that produce most of the total cloud effect on the TOA shortwave fluxes are deep convective, nimbostratus, and cirrostratus; and for the surface shortwave effect, the three most important cloud types are the three thickest cloud types, namely deep convective, nimbostratus, and stratus. With a realistic mix of cloud types, the cloud types that produce most of the total cloud effect on the shortwave fluxes (both TOA and surface) are the three cloud types with moderate optical thicknesses, stratocumulus, altostratus and cirrostratus.

With a uniform mix of cloud types, the three cloud types that produce most of the total cloud effect on the TOA longwave fluxes are the three high-level cloud types, deep convective, cirrostratus, and cirrus; and for the surface longwave effect, the three most important cloud types are stratocumulus, stratus, and altostratus. With a realistic mix of cloud types, the three cloud types that produce most of the total cloud effect on the TOA longwave fluxes are still the three high-level cloud types, but in a different order, cirrus, cirrostratus, and deep convective; but for the surface longwave effect, the three most important cloud types are stratocumulus, cumulus, and altostratus.

With a uniform mix of cloud types, the three cloud types that produce most of the total cloud effect on the in-atmosphere shortwave fluxes are cirrostratus, deep convective, and stratus, with the former two cloud types decreasing the shortwave heating and the last one increasing the shortwave heating. With a realistic mix of cloud types, the cloud types that produce most of the total cloud effect on the in-atmosphere shortwave fluxes are cirrostratus, cirrus, and stratocumulus, with the former two cloud types decreasing the shortwave heating and the last one increasing the shortwave heating.

With a uniform mix of cloud types, the three cloud types that produce most of the total cloud effect on the in-atmosphere longwave fluxes are deep convective, cirrostratus, and stratocumulus, with the former two cloud types decreasing the longwave cooling and the last one increasing the longwave cooling. With a realistic mix of cloud types, the cloud types that produce most of the total cloud effect on the in-atmosphere longwave fluxes are stratocumulus, cumulus, and cirrus, with the former two cloud types increasing the longwave cooling and the last one decreasing the longwave cooling.