Stratospheric water vapor and ozone response to different QBO disruption events in 2016 and 2020

Abstract

The Quasi-Biennial Oscillation (QBO) is a major mode of climate variability with periodically descending westerly and easterly winds in the tropical stratosphere, modulating transport and distributions of key greenhouse gases such as water vapor and ozone. In 2016 and 2020, anomalous QBO easterlies disrupted the QBO's 28-month period previously observed.Here, we quantify the impact of these two QBO disruption events on the Brewer-Dobson circulation, water vapour and ozone using the ERA5 reanalysis and satellite observations, respectively. Both lower stratospheric trace gases decrease globally during the 2015-2016 QBO disruption event, while they only weakly decrease during the 2019-2020 QBO disruption event.These dissimilarities in the circulation anomalous response to the QBO disruption events result from differences in the tropical upwelling caused by anomalous planetary and gravity wave forcing in the lower stratosphere near the equatorward flanks of the subtropical jet. The differences in the response of lower stratospheric water vapor to the 2015-2016 and 2019-2020 QBO disruption events are due to the cold-point temperature differences induced by the Australian wildfire, which moistened the lower stratosphere, therefore, hidding the 2019-2020 QBO disruption impact. Our results highlight the need for a better understanding of the causes of QBO disruption events, their interplay with other climate variability modes, and their impacts on water vapor and ozone in the face of a changing climate.