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. In this study, we propose a joint predictor involving the QBO for the Antarctic stratospheric polar vortex and ozone in austral spring. During the westerly QBO phase (WQBO), positive zonal-mean zonal wind anomalies at 20-40° S in the upper stratosphere in July, named the positive extratropical mode, can lead to a stronger Antarctic stratospheric polar vortex and lower ozone concentration in November, with correlations reaching 0.75 and -0.60, respectively. The mechanism is summarized as follows: the positive extratropical mode triggers a secondary circulation, which further alters the environmental conditions for wave propagation in the stratosphere. The resulting anomalous wave divergence leads to a stronger Antarctic stratospheric polar vortex during the austral spring, while during the easterly QBO phase (EQBO), the correlation between the extratropical mode and the strength of the polar vortex is only 0.1. Due to the stronger upward motion in the tropics, which opposes the secondary circulation induced 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 the WQBO could serve as a reliable predictor for both the Antarctic stratospheric polar vortex and the Antarctic ozone hole with a 4-month time lag.