A 3-DIMENSINAL TRANSPORT MODEL STUDY OF PSC PROCESSING DURING EASOE

A 3D transport model has been used to investigate the extent of processing of air by polar stratospheric clouds (PSCs) during the northern winter 1991-92 and the potential for subsequent ozone destruction. The model is forced using the winds and temperatures from the European Centre for Medium Range Weather Forecasts analyses and the transport of tracers is performed using a non-diffusive scheme, which is important when dealing with localised regions of PSCs. Model experiments have been performed from late November 1991 to the end of February 1992 with tracers introduced in the model to indicate the amount of air which has been processed by PSCs and the amount of time that this perturbed air has subsequently been exposed to sunlight. In the model experiments PSC processing started sporadically in December. By early January air in the polar lower stratosphere had been extensively processed. The occurrence of large-scale PSCs terminated with a minor warming in January. The inferred chemical ozone loss in the model experiments, while sensitive to some assumed parameters, is small and limited by the availability of sunlight.