The Antarctic ozone hole during 2017

We review the 2017 Antarctic ozone hole, making use of various meteorological reanalyses, and in-situ, satellite and ground-based measurements of ozone and related trace gases, and ground-based measurements of ultraviolet radiation. The 2017 ozone hole was associated with relatively high ozone concentrations over the Antarctic region compared to other years, and our analysis ranks it in the smallest 25% of observed ozone holes in terms of size. The severity of stratospheric ozone loss was comparable with that which occurred in 2002 (when the stratospheric vortex exhibited an unprecedented major warming) and most years prior to 1989 (which were early in the development of the ozone hole). Disturbances to the polar vortex in August and September that were associated with intervals of anomalous planetary wave activity resulted in significant erosion of the polar vortex and the mitigation of the overall level of ozone depletion. The enhanced wave activity was favoured by below-average westerly winds at high southern latitudes during winter, and the prevailing easterly phase of the Quasi- Biennial Oscillation (QBO). Using proxy information on the chemical makeup of the polar vortex based on analysis of nitrous oxide and the likely influence of the QBO, we suggest that the concentration of inorganic chlorine, which plays a key role in ozone loss, was likely similar to 2014 and 2016, when the ozone hole was larger than in 2017. Overall, we find that the overall severity of Antarctic ozone loss in 2017 was largely dictated by the timing of the disturbances to the polar vortex rather than interannual variability in the level of inorganic chlorine.