Abnormally Long Absence of Polar Stratospheric Clouds in the Arctic in Midwinter According to Satellite Observations

Abstract

Polar stratospheric clouds (PSCs) play a significant role in ozone depletion in the polar regions, acting as “surfaces” for heterogeneous reactions proceeding with the release of photochemically active molecular chlorine from late winter to early spring. Moreover, during the winter, chlorine “reservoirs,” which are reagents for heterogeneous reactions, accumulate on PSC particles. When PSC particles are destroyed in midwinter, the accumulation of chlorine compounds is interrupted, and from late winter to spring, ozone depletion is not observed even under conditions of the strong polar vortex, in the presence of newly formed PSCs. Using the vortex delineation method, we studied the dynamics of the Arctic polar vortex in the winters of 1984–1985, 1998–1999, 2001–2002, 2012–2013, and 2018–2019 as the reasons for the abnormally long absence of PSCs in the Arctic in midwinter, when they existed in January within no more than 5 days according to satellite observations. The PSC melting in these years was observed when the dynamic barrier of the polar vortex weakened due to a local decrease in wind speed along the vortex edge below 20 m/s in the lower stratosphere, which was recorded throughout almost all of January. These cases are the only examples of unusual weakening of the Arctic polar vortex in midwinter for the period from 1979 to 2022.