Abstract
The discovery of polar stratospheric clouds (PSC's) in the Arctic and Antarctic stratosphere during winter is described, and the directly observed and implied properties of these clouds are discussed. It is proposed that the more familiar "mother-of-pearl" or "nacreous" clouds are a special subset of PSC's. The size, location, prevalence and temperature dependence of the clouds as measured by the SAM II and SAGE satellite systems are outlined. Airborne lidar measurements have recently demonstrated that the PSC phenomenon is most probably associated with an extended stratospheric cloud bank existing within the cold polar vortex region during the winter period with the PSC's bounded by a 188 K temperature isotherm. The PSC's probably exist at a 50 percent frequency within the 193 K isotherm. Using the observed information on the cloud extinction and change in location with time we consider possible formation mechanisms, the size of the cloud particles, and show the descending motion of the cloud during wintertime.
