Quantifying the contribution of transport to Antarctic springtime ozone column variability

Abstract. Quantifying chemical and dynamical drivers of Antarctic ozone variability remains important as stratospheric chlorine levels gradually reduce and the ozone hole recovers in response. While chemistry dominates the formation of the ozone hole in September, the role of dynamics grows as the spring season progresses. To improve our ability to characterise the dynamical impacts on Antarctic total column ozone (TCO), we use MLS/Aura observations of carbon monoxide to trace the path of an air parcel that originates in the mesosphere and descends into the springtime polar vortex. We define a new metric, the Mesospheric Parcel Altitude (MPA), which measures the altitude of the descending mesospheric air parcel at the end of October. The MPA is highly correlated with October TCO and functions as a diagnostic tool, capturing the dynamical state of the inner-vortex. Based on the MPA, we classify October ozone holes from 2004–2024 into three mesospheric descent types (Strong, Regular, and Weak) and provide a formula to estimate the magnitude of horizontal ozone transport (poleward of 70° S and between 17–27 km) during a given October. A higher MPA (>26.9 km) indicates Weak descent, reduced ozone transport, and a larger, longer-lived ozone hole. A lower MPA (<24.6 km) indicates Strong descent, increased ozone transport, and a smaller, shorter-lived ozone hole. When the MPA is used as a proxy for polar cap TCO, approximately 63 % of the observed variance during October is explained by the metric.