The Antarctic Polar Vortex, Stratospheric Ozone, and its Impacts

The Antarctic polar vortex is typically stronger and less variable than the Arctic polar vortex. However, the associated ozone concentration significantly varies from year to year and from decade to decade due to wave forcing and ozone depleting substances, affecting Southern Hemisphere surface climate in austral spring and summer.

On interannual timescale, stratospheric ozone concentration in September is negatively correlated with the Southern Annular Mode index in October. This co-variability results in a systematic change in precipitation and surface air temperature that is comparable to and independent of the one associated with El Niño-Southern Oscillation and the Indian Ocean Dipole Mode. In consistent with the time-lagged downward influence, the operational model shows an improved surface prediction in October by prescribing more realistic stratospheric ozone distribution.

On decadal timescale, the ozone depletion and the polar vortex strengthening, in response to the increasing ozone depleting substances in 20th century, is robustly found in climate models with varying complexity. Both Coupled General Circulation Models (CGCMs) and Chemistry-Climate Models (CCMs) exhibit a poleward intensification of westerly jet and a poleward expansion of the Hadley cell in austral summer as stratospheric ozone concentration decreases. The CCMs with and without ocean coupling show quantitatively similar multi-model mean trends. The results are also quantitatively similar to those derived from the CGCMs in which stratospheric ozone is prescribed with monthly- and zonally-averaged values. These results suggest that the ozone-hole-induced Southern Hemisphere circulation changes are robust across the models irrespective of the specific chemistry-atmosphere-ocean coupling. The projected change in stratospheric ozone and its possible impacts are also briefly discussed.