1271 - 1274 , June 18 , 1993 a 3 D Simulation of the Early Winter Distribution of Reactive Chlorine in the North Polar Vortex

Abstrac.____ t Early in December 1991, high values of C10 are seen by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite at latitudes outh of areas of temperatures cold enough to form polar stratospheric clouds (PSC's). A three dimensional simulation shows that the heterogeneous conversion of chlorine reservoirs to reactive chlorine on the surfaces ofPSC's (processing) takes place at high latitudes. Often the "processed" air must be transported to lower latitudes, where the reactive chlorine is photochemically converted toC10, to be observed byMLS. In this simulation, one incidence of cold temperatures is associated with an anticyclone, and a second with a cyclone. The transport ofprocessed airassociated with the anticyclone is marked by shearing; a decrease in the maximum of the processed air is accompanied by growth of the area influenced by the processing. In contrast, the air processed in the cyclonic event spreads more slowly. This shows that transport and shearing is a crucial element o the evolution of reactive chlorine associated with a processing event. In particular, transport and shearing, as well as photochemical processes, can cause variations in observed CiO.