Understanding the Role of QBO-Driven Variability in Observed Changes in Ozone from the Middle Stratosphere to the Troposphere and across Multiple Time Scales

Susan Solomon’s research was pivotal to the establishment of the Montreal Protocol on Substances that Deplete the Ozone Layer. The 2018 Scientific Assessment of Ozone Depletion summarized compelling evidence of ozone recovery in the tropical upper stratosphere, with about half of the increase since 1997 attributed to the decline in ozone depleting substances in accordance with the Protocol. At the same time, the Assessment also highlighted the role of natural variability in complicating the detection of trends in lower stratospheric ozone. The large fluctuations in lower stratospheric ozone combined with large uncertainties in tropospheric ozone trends further poses a challenge for assessing the consistency of total column and ozone profile trends and for understanding when we should expect to see evidence of recovery in near-global (60S-60N) total column ozone. An improved understanding of the drivers of dynamical variability in ozone throughout the atmosphere and across multiple timescales is critical to finding new methods for accounting for natural changes in ozone when assessing anthropogenically-driven trends. The role of the QBO in trace gas variability from the middle stratosphere to the Earth’s surface has been shown by multiple recent studies to be greater than previously thought, with changes in the length and seasonal timing of the Easterly shear phase and its relationship to ENSO being particularly important to decadal-scale variability in ozone and other trace gases. I will present a measurement- and model-based assessment of this QBO-driven variability and discuss how it impacts our overall understanding of ozone trends over the past several decades.