Cloud particle phase determination with the AVHRR

An accurate determination of cloud particle phase is required for the retri eval of other cloud properties from satellite and for radiative flux calcul ations in climate models. The physical principles underlying phase determin ation using the advanced very high resolution radiometer (AVHRR) satellite sensor are described for daytime and nighttime, cold cloud and warm cloud c onditions. It is demonstrated that the spectral properties of cloud particl es provide necessary, but not sufficient, information for phase determinati on, because the relationship between the cloud and surface temperatures is also important. Algorithms based on these principles are presented and test ed. Validation with lidar and aircraft data from two Arctic held experiment s shows the procedures to be accurate in identifying the phase of homogeneo us water and ice clouds, though optically thin, mixed-phase, and multilayer clouds are problematic.