Climatology and Trends in the Forcing of the Stratospheric Ozone Transport in the ERA-40

A thorough analysis of the ozone transport was carried out using the Transformed-Mean Eulerian (TEM) tracer transport equation and the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). This study provides further insight into the role of the eddy ozone transport and its fundamental role in the recovery of the ozone hole during spring. Furthermore, a trend analysis of the wave forcing of the ozone transport reveals that while the largest intensification of the ozone chemical destruction coincides with the timing of the Antarctic ozone depletion, from September to November, it is rather weaker trends in the ozone chemistry earlier in the SH winter that cause the ozone hole. That is because, in the SH from October to December, an equally large trend in the eddy transport, associated with a small increase of the mean transport, balances the trend in the chemical destruction. The increase in the spring eddy ozone transport is due to an increase in the meridional ozone gradient associated with the ozone hole. Thus a stronger mixing takes place near the edge of the polar vortex between ozone-rich and ozone-poor regions.

This study shows that the increase in the eddy transport is characterized by more poleward ozone eddy flux, which is forced by transient waves in the midlatitudes and by stationary waves in the polar region. This is primarily due to the presence of storm tracks in the midlatitudes and of the asymmetric Antarctic topography and ice-sea heating contrasts near the pole. Overall, this study makes clear of the fact that without an increase in the eddy ozone transport over the 1980-2001 time period, the ozone hole over Antarctica would be drastically more severe. This underlines the importance of the dynamical transport of ozone in the stratospheric ozone cycle and the need for careful diagnostics of the eddy ozone transport in modeling studies of long-term changes in stratospheric ozone.