Consequences of weakening of dynamic barrier of the Arctic polar vortex

The dynamic barrier is one of the physical characteristics of the polar vortices; it prevents subpolar air masses from penetrating into the vortex and contributes to a temperature decrease inside the vortex in the lower stratosphere. In the presence of a dynamic barrier in winter, chlorine compounds involved in the ozone destruction cycle accumulate on particles of polar stratospheric clouds (PSCs) and heterogeneous reactions occur with the formation of molecular chlorine, and with the appearance of solar radiation over the polar region, photochemical reactions begin, leading to large-scale ozone depletion. When the dynamic barrier is weakened in winter, the temperature inside the vortex rises, PSC melts and, thus, the accumulation of chlorine cycle reagents on PSC is interrupted. We proposed dividing the Arctic polar vortex dynamics into 3 types according to the consequences: (1) the strong vortex, whose activity results in ozone depletion, (2) the weak vortex with breakdown in winter, marked by a sudden stratospheric warming, and (3) the stable vortex with an episode (episodes) weakening of the dynamic barrier in winter without ozone depletion in the period from late winter to spring. We have for the first time proposed a characteristic of the dynamic barrier of the polar vortex at all pressure levels from 100 to 1 hPa and described the consequences of its weakening. Using the vortex delineation method based on the data of the ERA5 and MERRA-2 reanalyses, we showed that in all cases when the polar ozone depletion was not recorded from late winter to spring under the conditions of the stable polar vortex, the dynamic barrier weakening and PSС melting was observed in midwinter.