Early evolution of the ozone mini-hole generated by the Australian bushfires 2019–2020 observed from satellite and ground-based instruments

Abstract

The intense wildfires in Australia, during the 2019–2020 fire season, generated massive pyrocumulonimbus (pyro-Cb) clouds, and injected an unprecedented amount of smoke aerosols into the upper troposphere–lower stratosphere (UTLS). The smoke aerosols produced a self-sustaining confined anticyclonic vortex, that ascended up to 35 km altitude by March 2020 by diabatic heating of radiation absorbing aerosols. This vortex transported ozone-poor tropospheric air into the ozone-rich stratosphere, thus forming a transient ozone mini-hole. This study investigates the early evolution of the dynamically-generated ozone mini-hole, using satellite and ground-based observations, supported by modelling information. Ozone anomalies within the vortex are tracked and quantified by satellite observation. In particular, ad-hoc in-vortex observations are derived by coupling the IASI (Infrared Atmospheric Sounding Interferometer) satellite observations and meteorological reanalysis information of the vortex. With these observations, a 30 %–40 % ozone reduction is observed immediately after the event in a 6 km partial stratospheric column, which exponentially decreased to ∼ 7 % by the end of January with an e-folding time of about one week, as the vortex ascended in the stratosphere. A total ozone column reduction of ∼ 7 %, immediately after the pyro-Cb injection, was observed with IASI and the TROPOMI (TROPOspheric Monitoring Instrument) satellite instrument. Consistently, ground-based measurement at Lauder, New Zealand showed a localised ozone reduction reaching ∼ 10 % (total column) and ∼ 20 % (in-vortex stratospheric partial column) associated with two vortex overpasses. These results provide insights into the impacts of extreme wildfires and pyro-Cbs on the dynamics and composition of the stratosphere.