The Quasi-Biennial Oscillation and Tracer Transport Across Multiple Timescales

Abstract:

Understanding the drivers of dynamical variability in stratospheric trace gases across multiple timescales is critical to finding new methods for accounting for natural variability when assessing anthropogenically-driven trends. The role of the Quasi-Biennial Oscillation (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. Here, we use the Whole Atmosphere Community Climate Model and satellite observations to show that changes in the relative duration of easterly and westerly shear phases of the Quasi-Biennial Oscillation (QBO) can drive decadal-scale circulation variations that are likely to make detection of long-term changes challenging given the length of observational records. We further show that these QBO-driven changes to the circulation explain the observed latitudinally asymmetric trends in long-lived trace gases in the stratosphere over the period 2004-2012. The relationships we identify between the duration of QBO shear phases and trace gas transport are robust over other periods and can be accounted for in the calculation of trace gas trends using a simple index. In recent years, however, the 2015/16 and 2019/2020 QBO disruptions have changed the efficacy of this index for describing decadal-scale variability associated with the QBO. We analyze the impact of these disruptions on trace gas transport and assess how their impact can be incorporated in long-term trend analysis.