MID-STRATOSPHERIC OZONE MINIMA IN POLAR-REGIONS

Recent springtime measurements of ozone vertical profiles in polar reg ions have revealed local ozone depressions of about 25% at altitudes n ear 30 km. Similar features are also identified in three-dimensional p hotochemical model results. The modeled ozone depressions are local an d temporary, often associated with stratospheric warming events which transport air from low latitudes, altering its photochemical history. The feature may be a component of the climatology of the region, but o ccurs less frequently in the model, possibly because of the long-stand ing problem of the underprediction of upper stratospheric ozone.