The Southern Hemisphere (SH) zonal-mean circulation change in response to Antarctic ozone depletion is re-visited by examining a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models reasonably well reproduce Antarctic ozone depletion in the late 20th century. The related SH-summer circulation changes, such as a poleward intensification of westerly jet and a poleward expansion of the Hadley cell, are also well captured. All experiments exhibit quantitatively the same multi-model mean trend, irrespective of whether the ocean is coupled or prescribed. Results are also quantitatively similar to those derived from the Coupled Model Intercomparison Project phase 5 (CMIP5) high-top model simulations in which the stratospheric ozone is mostly prescribed with monthly-and zonally-averaged values. These results suggest that the ozone-hole-induced SH-summer circulation changes are robust across the models irrespective of the specific chemistry-atmosphere-ocean coupling.

<p> The impacts of stratospheric ozone and greenhouse gas changes on the Southern Hemisphere (SH) climate are re-visited by examining the single forcing experiments from the Chemistry-Climate Model Initiative (CCMI) project. In particular, the fixed ozone-depleting substance (ODS) runs and the fixed greenhouse gas (GHG) concentration runs are directly compared with the reference runs for both the past and future. Consistent with the previous studies, the SH-summer general circulation changes, such as changes in the jet location, Hadley cell edge, and Southern Annular Mode (SAM), show the opposite trends from the past to the future in response to the Antarctic ozone depletion and recovery. The GHG-induced circulation changes largely enhance the ozone-induced circulation changes in the past, but partly cancel them in the future. The ozone recovery-related tropospheric circulation return dates are also estimated in this study. We will further discuss the inter-model diversity among the CCMI models.</p>

<p>The Antarctic polar vortex and the associated ozone change have been recognized as a key factor that influences both local and large-scale circulations in the Southern Hemisphere (SH) extratropics. Their downward impacts are also evident in the subseasonal-to-seasonal (S2S) and long-term climate predictions especially in austral spring and summer. However, most operational S2S models, including the Global Seasonal Forecasting System version 5 (GloSea5), use climatological ozone and ignore time-varying ozone associated with polar vortex variability. This study explores the possible impact of stratospheric ozone on SH S2S prediction skill by conducting the two sets of reforecast experiments with the GloSea5. The reforecasts are initialized on 1st September of every year for the period of 2004-2018 with either climatological or observed ozone from the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) data. It turns out that the reforecasts with observed ozone have an improved prediction skill at 5- and 6-week lead forecasts than those with climatological ozone. The surface prediction skills also increase over the southern Australia and New Zealand. These results suggest that more realistic stratospheric ozone forcing could improve the SH prediction skill on subseasonal-to-seasonal timescale.</p>