Reply on RC1

Abstract

Balloon-borne ozonesondes launched weekly from South Pole station (1986–2021) measure high vertical resolution profiles of ozone and temperature from surface to 30–35 km altitude. The launch frequency is increased in late winter before the onset of rapid stratospheric ozone loss in September. Ozone hole metrics show the yearly total column ozone and 14–21 km column ozone minimum values and September loss rates remain on an upward (less severe) trend since 2001. However, the data series also illustrate interannual variability, especially in the last three years (2019–2021). Here we show additional details of these three years by comparing minimum ozone profiles and the July–December 14–21 km column ozone time series. The 2019 anomalous vortex breakdown showed stratospheric temperatures began warming in early September leading to reduced ozone loss. The minimum total column ozone of 180 Dobson Units (DU) was observed on 24 September. This was followed by two stable and cold polar vortex years in 2020 and 2021 with total column ozone minimums at 104 DU (01 October) and 102 DU (07 October), respectively. These years also showed broad zero ozone (saturation loss) regions within the 14–21 km layer by the end of September which persisted into October. Validation of the ozonesonde observations is conducted through the ongoing comparison of total column ozone (TCO) measurements with the South Pole ground-based Dobson spectrophotometer. The ozonesondes show a constant positive offset of 2 ± 3 % (higher) than the Dobson following a thorough evaluation/homogenization of the ozonesonde record in 2018.