3-DIMENSIONAL MODELING OF CHLORINE ACTIVATION IN THE ARCTIC STRATOSPHERE

The UK universities Global Atmospheric Modelling Programme (UGAMP) Gen eral Circulation Model has been used to study the chemical evolution o f the northern hemisphere polar vortex. A run that includes a parametr isation of the heterogeneous reactions occurring on polar stratospheri c clouds (PSCs) has been initialised with the ECMWF analyses of the 5t h of January 1992. This run produces high values of active chlorine wi thin the polar vortex, for example mixing ratios of ClO(X) (=CL+CLO+CL 2O2) of 1.8ppbv are calculated after six days of integration, with cor respondingly low values of HCl and CLONO2. During warm periods of this model run, when the PSC reactions are not active, the ClO(X) is conve rted slowly back into ClONO2. Chemical loss of ozone in January in the model is small.