Vertical Dynamics of the Stratospheric Polar Vortices during their Anomalous Strengthening in 2020

Abstract

Stratospheric polar vortices, which form over the polar regions in late autumn, are large-scale cyclonic structures whose stability in the winter-spring period determines the scales and depth of spring ozone depletion. Using the vortex delineation method based on ERA5 reanalysis data, we studied the features in the vertical dynamics of the Arctic and Antarctic polar vortices in 2020 during their anomalous strengthening, which was accompanied by deep and prolonged ozone depletion in the Arctic and Antarctic. In particular, we examined the synchronicity in temporal changes at different stratospheric levels. The polar vortex breakdown in 2020 was observed from late spring to early summer spreading from top downward over 1‒2 months. The dynamics of the Arctic polar vortex showed three peaks of activity, spreading from the upper to the lower stratosphere within a month. The dynamics of the Antarctic polar vortex clearly showed one peak of activity spreading from the upper to the lower stratosphere over a period of 2 months. The anomalous duration of the westerly phase of the quasi-biennial oscillation in the middle stratosphere has been proposed as a possible reason for the unprecedented strengthening of the polar vortices in 2020. The results can be used to assess the risks of increasing ground-level UV-B radiation which is dangerous for the biosphere.