A MICRO-PHYSICAL BOX MODEL FOR EASOE - PRELIMINARY-RESULTS FOR THE JANUARY FEBRUARY 1990 PSC EVENT OVER KIRUNA

First results of a trajectory box model designed for the European Arctic Stratospheric Ozone Experiment (EASOE) are presented. The model contains a comprehensive description of both types of polar stratospheric particles, NAT on aerosol (Type-I) and ice on NAT (Type-II), including nucleation, growth/evaporation, and sedimentation of particles. The performance of the model is tested for the case of the polar stratospheric cloud (PSC) event January 31-February 1, 1990 over Kiruna (north Sweden). Comparison of the model results with measurements from two stratospheric balloon flights shows that the theory can reproduce the data provided the following two conditions are satisfied: (a) a strong lee wave activity was present at the time of the balloon flights; (b) the nucleation of NAT on H2SO4 is either governed by a high barrier energy or delayed due to insufficient freezing of the background aerosol. These results indicate an urgent need for both, the implementation of lee wave effects into the existing trajectory models and a better understanding of the NAT nucleation on the background aerosol.