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The dynamic barrier of the polar vortex prevents the penetration of air masses into the vortex and contributes to the preservation of extremely low temperatures inside the vortex. The melting of polar stratospheric clouds in winter occurs as a result of the dynamic barrier weakening in the lower stratosphere. The dynamic barrier exists when the wind speed over the entire edge of the polar vortex is more than 20, 26 and 30 m/s respectively at the 50, 20 and 10 hPa levels. We studied the dynamics of the Arctic polar vortex in the winter-spring of 2017/2018 before and after its splitting on 10 February at the 50, 20 and 10 hPa levels by the vortex delineation method using geopotential. In the middle stratosphere, since 15 February, an irreversible breakdown of the polar vortex was observed (the dynamic barrier weakening and the vortex area decrease below 10 million km2 ), and in the lower stratosphere at the 50 hPa level, a short-term recovery of the dynamic characteristics of the polar vortex was observed from 9 to 17 March. The case of 2017/2018 is one of the exceptions, when the collapsing cyclone experienced a short-term recovery of the polar vortex characteristics in the lower stratosphere in spring after the vortex area decreased below 10 million km2 and the dynamic barrier weakened.
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