Modulation of Antarctic vortex composition by the quasi-biennial oscillation

Using a decade of Aura Microwave Limb Sounder observations, we show distinctly different N2O distributions in Southern Hemisphere winter that depend on the phase of the quasi-biennial oscillation (QBO). Composites of the nitrous oxide (N2O) anomalies calculated for westerly and easterly phases show that QBO-generated variability originating in the subtropical middle stratosphere fills the midlatitude surf zone by late winter. After the spring vortex breakup, the anomaly is transported to the Antarctic where it remains until the next vortex forms in fall. Trapped in the newly formed vortex, the anomaly descends in isolation through fall and winter, arriving in the Antarctic lower stratosphere in September—about 1 year after it formed. This transport pathway explains previously reported variability of N2O and inorganic chlorine (Cly) inside the Antarctic vortex and demonstrates that the middle stratosphere QBO affects ozone depletion by modulating Antarctic Cly.