Evolution of observed ozone, trace gases, and meteorological variables over Arrival Heights, Antarctica (77.8°S, 166.7°E) during the 2019 Antarctic stratospheric sudden warming

Abstract

We use ground-based spectroscopic remote sensing measurements of the stratospheric trace gases O₃, HCl, ClO, BrO, HNO₃, NO₂, OClO, ClONO₂, N₂O and HF, along with radiosonde profiles of temperature to track the springtime development of the 2019 ozone hole over Arrival Heights (77.8°S, 166.7°E, AHTS), Antarctica, during, and after, the 2019 stratospheric sudden warming (SSW) event. Both measurements and model simulations show that the 2019 SSW caused an extraordinarily warm stratosphere within the polar vortex, resulting in record low ozone depletion over AHTS. We also contrast the evolution of the 2019 ozone hole to that in 2002, which also had a major springtime SSW event.

The SSW event started around 28^th August. By ∼17^th September, stratospheric temperatures inside the polar vortex over AHTS were ∼45 K higher than the climatological average. The SSW did not cause an en masse displacement of mid-latitude air over AHTS as in the 2002 SSW event. However, the increased temperatures did cause an unusually early reduction in polar stratospheric clouds, halting the denitrification early and leading to increased gas-phase HNO₃ and record high levels of NO₂ (‘renoxification’). This caused the earliest observed deactivation of chlorine, returning all active chlorine into the chlorine reservoir species, HCl and ClONO₂. The deactivation rate into HCl remained relatively unaffected by the SSW, whilst there was a dramatic increase in ClONO₂ formation. This chlorine deactivation pathway via ClONO₂ is typical of the Arctic and atypical for the Antarctic.

At AHTS, record high levels of springtime ozone were observed. The measured ozone total column did not drop below 220 DU. Record high stratospheric temperatures persisted until 7^th October over AHTS. By 22^nd October, AHTS was not beneath the polar vortex. The polar vortex break-up date on 9^th November was one of the earliest observed.

Keywords:

• Arrival Heights
• Antarctica
• stratospheric sudden warming
• polar heterogeneous ozone depletion chemistry

Acknowledgements

We would like to thank NIWA meteorologists Ben Noll and Nava Fedaeff for suppling Fig. 1 along with discussions concerning the meteorology of the 2019 SSW event, Antarctica New Zealand for providing logistical support for the measurements at Arrival Heights and Scott Base, and the McMurdo USAP weather forecasting team.

We appreciate the support of the University of Wisconsin-Madison and Madison College AMRDC for the use of the radiosonde data set, NSF grant numbers 1924730 (UW) and 1951603 (MATC).

Disclosure statement

The authors declare that there are no conflicts of interest regarding the publication of this article.

Additional information

Funding

Measurements at Arrival Heights and Scott Base are core‐funded by NIWA through New Zealand's Ministry of Business, Innovation and Employment Strategic Science Investment Fund. The ClO measurements at Scott Base are supported by the NASA Upper Atmosphere Research Program