Idealized modeling of the impacts of the ozone hole on Southern Hemisphere climate

Recent studies suggest that Southern Hemisphere tropospheric circulation changes in austral summer over the second half of the twentieth century have been caused primarily by polar stratospheric ozone depletion, and, in particular, that ozone depletion leads to a poleward jet shift that extends all the way to the surface. Stratospheric ozone depletion cools the polar stratosphere, changes the north-south temperature gradient and extends the persistence of the Antarctic polar vortex (i.e. it delays the stratospheric final warming). In this study, we use an idealized model setup that is forced by relaxation to an equilibrium temperature that varies seasonally only in the stratosphere. This enables us to attribute any seasonal tropospheric changes unambiguously to the stratospheric seasonal cycle. We perturb the model with a seasonal polar stratospheric cooling to mimic the effects of stratospheric ozone depletion. In response, the model produces a statistically significant temperature anomaly in the stratosphere, a delay in the timing of final warming events, and a strengthened polar vortex that extends downwards into the troposphere in the summer. At the surface, the response extends well beyond the polar latitudes. We examine changes to the zonal wind structure that alter the propagation of planetary waves into the stratosphere. We also study the persistence of the tropospheric response and its link to the model's tropospheric annular mode timescale.