RECENT TRENDS IN OZONE IN THE UPPER-STRATOSPHERE - IMPLICATIONS FOR CHLORINE CHEMISTRY

We have studied the implications of recent trends in the annual mean a nd the amplitude of the annual harmonic of ozone in the upper stratosp here from the 15 years of the combined data from the Nimbus-7 SBUV and the NOAA-11 SBUV/2 instruments. This was done in the context of the G SFC 2D model predictions of these trends which are based on plausible scenarios of anthropogenic Cly increase in the atmosphere. The compari son of the observed and model-estimated annual mean ozone trends show some similarity in their latitude and altitude characteristics. Both t he model and data show a maximum ozone decrease of -6 to -10% per deca de at high latitudes in the upper stratosphere. However, there are als o significant differences between the observed and computed trends whi ch may be related to both the model uncertainty and the uncertainty fo r the long term instrument drift. The observations also suggest a decr ease of 10-25% per decade in the annual amplitude of ozone at 2 mb bet ween 40-degrees-60-degrees in both hemispheres, with a relatively larg er interannual variability in the northern hemisphere. These values ar e in general agreement with the model predictions and thus provide add itional support in favor of the chlorine induced changes in ozone in t he upper stratosphere.