ACCESS-CM2-Chem: evaluation of southern hemisphere ozone and its effect on the Southern Annular Mode

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Abstract
Chemistry–climate models are important tools for forecasting the evolution of climate. Of particular importance is the simulation of Antarctic ozone depletion due to its effect on the Southern Annular Mode (SAM). In this paper we evaluate the chemistry–climate model ACCESS-CM2-Chem. We find the simulation of stratospheric ozone by ACCESS-CM2-Chem to be significantly improved relative to its predecessor, and as good as the best of the contemporary chemistry–climate models – the ensemble of which displays considerable variation. We also find that the trend in summertime SAM is simulated well by ACCESS-CM2-Chem compared to the ERA5 reanalysis. Further, we show that this trend is more sensitive to changes in ozone depletion forcing in ACCESS-CM2-Chem than the equivalent model with prescribed ozone. However, a downside of the interactive chemistry of ACCESS-CM2-Chem, relative to the prescribed chemistry version, is an increase in the bias towards later vortex break-ups. Many recent studies have identified the important role of feedbacks between interactive ozone chemistry and climate. This phenomenon will be crucial to understand future projections where the recovery of stratospheric ozone will interact with increasing greenhouse gas driven warming. Based on the performance demonstrated here, ACCESS-CM2-Chem is a promising model with which to further this line of research, although the delay in the vortex break-up induced by the interactive chemistry is an issue that requires further work.

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