DENITRIFICATION THROUGH PSC FORMATION - A 1-D MODEL INCORPORATING TEMPERATURE OSCILLATIONS

A one-dimensional model of polar stratospheric cloud (PSC) formation and evolution during the polar winter, incorporating both HNO3 and H2O condensation, has been developed to investigate the interactions between Type I and Type II PSCs and the effects of these clouds on the stratospheric composition. Model simulations for various meterological conditions and the results of extensive sensitivity tests are presented. Temperature oscillations, which have been included in the model, are shown to have an important influence on the characteristics and effects of the PSCs. The predicted proportions of the PSCs are consistent with observations of number, size, and optical effects, such as depolarization. Denitrification of stratospheric air by 35-88% is shown to occur in the presence of both Type I and Type II PSCs, with comparable nitrate removal in both types of clouds. Dehydration by Type II clouds simultaneously removes similar percentages of water vapour, up to 79% at lower altitudes. Although dehydration is insensitive to most of the parameter variations except the minimum temperature, the process of denitrification, especially the proportion removed by Type I PSCs, is highly variable.