Record‐High Ozone in the Austral Mid‐Latitude Tropopause Region Driven by Dynamical and Chemical Effects of the 2019 Sudden Stratospheric Warming

Abstract

In January 2020, tropopause‐level ozone in the austral mid‐latitudes was the highest everobserved in the available Microwave Limb Sounder data record since 2004. Two extreme events preceded thisanomaly: the Australian Black Summer fires and the 2019 sudden stratospheric warming (SSW), raising thequestion of how these disruptions influenced Southern Hemisphere ozone. Here, we investigate the dynamicaland chemical contributions to the ozone anomaly using a chemistry‐climate model and satellite observations.We find that downward transport of polar ozone‐enriched air due to the SSW later spread equatorward. Suchtransport together with photochemical ozone production from emissions of wildfires (fueled by dry and hotconditions previously attributed to the SSW) increased tropopause‐level ozone by up to 30 ppb, with transport asthe dominant factor (around 80%). While chemical ozone production from wildfires is well‐recognized, ourresults highlight that SSWs can greatly influence mid‐latitude ozone through dynamical effects.