ON THE DISTRIBUTION OF COLD-AIR NEAR THE VORTEX EDGE IN THE LOWER STRATOSPHERE

The horizontal distributions of air in the temperature ranges -70-degr ees>T>-77-degrees-C, -77-degrees>T>-85-degrees-C and T<-85-degrees-C h ave been examined during the Arctic winter of 1988/1989 and the Antarc tic winter of 1987, using T106 European Centre for Medium-range Weathe r Forecasts (ECMWF) analyses of standard meteorological variables and potential vorticity. ER-2 airborne data were used to define, using wat er vapor and nitrous oxide observations, a potential vorticity (PV) co ntour corresponding to a chemically defined vortex edge. The jet strea m axis was used to select a PV contour corresponding to the maximum wi nds, or a dynamically defined vortex edge. Air in the range -70-degree s>T>-77-degrees-C was confined within the dynamically defined Arctic v ortex, with only small fractions appearing outside the chemically defi ned vortex. In the Antarctic, up to 14% of this air was outside the ch emically defined vortex but very little was outside the dynamically de fined vortex. After late January (Arctic) and late August (Antarctic), respectively, the chemically defined vortices shrank, being 27% and 2 0% smaller in February and September. The dynamically defined vortices remained essentially constant in area. There were no occurrences of n ominal type II polar stratospheric clouds (PSCs) outside either vortex , however defined. One implication of these results is that heterogene ous conversion of ClONO2 and HCI to reactive forms of chlorine is conf ined almost entirely to the Arctic vortex, while some such conversion may occur at the edge of the Antarctic vortex. However, small and infr equent areas of air in the range -77-degrees>T>-85-degrees-C did occur immediately outside both vortices, so separating the effects of peel- off, type I PSCs and sulfuric acid aerosol processing may be difficult on occasions. What is clear is that all three processes are intimatel y associated with the polar night jet stream.