Factors Contributing to the Unusually Low Antarctic Springtime Ozone in 2020–2023

The 2020–2023 Antarctic spring seasons saw large ozone holes, substantial ozone mass deficit, and low polar cap total ozone compared to the second decade of the 21st century, prompting questions about the pace of ozone recovery over Antarctica. We use a stratospheric composition reanalysis developed at the NASA Global Modeling and Assimilation Office and chemical ozone loss estimates derived from NASA's Aura Microwave Limb Sounder observations to identify the key factors contributing to these unusually large ozone holes. We find that the below-average Antarctic total column ozone and large ozone holes in each of the years of interest resulted from a different combination of the following: anomalously low ozone within the stratospheric polar vortex, strong chemical ozone depletion, weak dynamical ozone resupply, and the size and geometry of the polar vortex. We also interpret our findings in the broader context of ozone recovery, with a particular focus on September, the month when signs of recovery are most evident. We find no evidence challenging the current consensus that springtime Antarctic ozone is recovering in response to the implementation of the Montreal Protocol and its amendments.