A parameterisation of the effective radius of ice free clouds for use in global climate models

Abstract

The variation of the droplet effective radius with height above cloud base and liquid water content has been examined for several different cloud types forming in widely separated parts of the world. The clouds examined are marine stratocumulus over the Pacific Ocean, cumulus clouds forming over continental USA, cap clouds enveloping Great Dun Fell in the UK, and stratocumulus and small cumulus clouds forming over the UK. The clouds differ markedly in their behaviour due principally to the large variation in the concentration of cloud condensation nuclei between the oceans and the continents and the differing roles of dry air entrainment in the different cloud types. The latter effect is seen to be a maximum in cumulus clouds which are strongly affected by the mixing process. Radiative cooling from the stratocumulus is also significant in these cloud types. The results obtained have been used to suggest improvements to the input data used in the parameterisation of the radiative properties of clouds in Global Climate Models.