The Joint Effect of Mid-latitude Winds and the Westerly Quasi-Biennial Oscillation Phase on the Antarctic Stratospheric Polar Vortex and Ozone

Abstract. The quasi-biennial oscillation (QBO) dynamically interacts with the extratropical atmosphere. However, the relationship between the QBO in austral winter and the Antarctic stratospheric polar vortex in spring remains unclear. Here, we proposed a joint predictor involving the QBO for the Antarctic polar vortex and ozone in austral spring. During the westerly QBO phase (WQBO), positive anomalies in the zonal-mean zonal wind at 20° S−40° S in the upper stratosphere in July, named as the extratropical positive mode, can lead to a stronger Antarctic stratospheric polar vortex and lower ozone concentration in November, with correlations reaching 0.75 and 0.60. The mechanism is summarized as follows: the positive extratropical mode triggers a secondary circulation, which further alters the environmental condition for wave propagation in the stratosphere, pushing the positive anomalous zonal-mean zonal wind towards the pole. While during the easterly QBO phase (EQBO), the correlation of the extratropical mode and the strength of polar vortex is only 0.1. Due to stronger upward motions in the tropics, which opposes the secondary circulation caused by the extratropical mode, the EQBO cannot sustain the positive anomalous zonal-mean zonal wind until November. Our results highlight that the extratropical mode during WQBO could serve as a reliable predictor of the Antarctic stratospheric polar vortex and Antarctic ozone hole with a five-month time lag.