Features of the stratospheric polar vortex weakening prior to breakdown
V.V. Zuev, E.S. Savelieva, A.V. Pavlinsky
Institute of Monitoring of Climatic and Ecological Systems of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
Keywords: stratospheric polar vortices, polar stratospheric clouds, polar vortex edge, polar vortex area, wind speed along the vortex edge
Abstract
We consider the features of the weakening of the stratospheric polar vortex that precede its breakdown. To analyze the abnormal dynamics of the polar vortices, we used the method of estimating the main parameters of the vortex by delineating its edges using the geopotential values determined from the maximum temperature gradient and maximum wind speed according to the ERA5 reanalysis data. As a result, we showed that the criteria for the abnormal weakening of the polar vortex preceding its breakdown is a decrease in the vortex area to less than 10 million km2 and a subsequent decrease in the average wind speed along the vortex edge below 30 and 45 m/s in the lower and middle stratosphere, respectively. In this case, the polar vortex becomes a small cyclone (characterized by high temperatures and the absence of a dynamic barrier) and collapses within three weeks.
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