Comparing the impacts of tropical SST variability and Polar stratospheric ozone loss on the Southern Ocean westerly winds

In summer, the model simulates a positive SAM-like pattern, to which ozone depletion and tropical SSTs (which contain signatures of internal variability and warming from greenhouse gasses) contribute. In autumn, the ensemble-mean response consists of stronger westerlies over the Pacific sector, explained by a Rossby wave originating from the central equatorial Pacific. While these responses resemble observations, attribution is complicated by intrinsic atmospheric variability.

In the experiments forced only with tropical SSTs, individual ensemble members exhibit wind trend patterns that mimic the forced response to ozone. When the analysis presented herein is applied to 1960-2000, the primary period of ozone loss, ozone depletion largely explains the model's SAM-like zonal wind trend. The time-varying importance of these different drivers has implications for relating the historical experiments of free-running, coupled models to observations.