ABSORPTION FEEDBACK IN STRATOCUMULUS CLOUDS - INFLUENCE ON CLOUD-TOP ALBEDO

This paper proposes a feedback mechanism which modifies the enhancement of cloud top albedo expected from an increased concentration of cloud condensation nuclei (CCN). The mechanism is based on the thermodynamic tendency of the cloud to stabilize itself against changes in the absorption of solar radiation. For optically thin clouds, this absorption feedback leads to a reduction in the anticipated albedo enhancement, while for optically thick clouds, an amplification of the albedo enhancement is predicted. The likely impact of this effect on the radiative forcing of climate due to changes in CCN and hence cloud top albedo is discussed.