فهرست نشریات علمی دسترسی آزاد ایران

The Arctic polar vortex is characterized by significant interannual and intraseasonal variability, causing instability of processes occurring in the winter-spring period in the polar stratosphere of the Northern Hemisphere. The dynamic barrier in the lower stratosphere leads to a decrease in temperature within the polar vortex, which is necessary for the formation of polar stratospheric clouds involved in the chlorine cycle of ozone depletion. In the middle and upper stratosphere, the dynamic barrier prevents air masses from the subpolar region from penetrating into the vortex, isolating the atmosphere inside the vortex from the outside. Using the vortex delineation method, based on the ERA5 reanalysis data, we examined the criteria for the weakening of the dynamic barrier in the middle and upper stratosphere and the features of the vertical dynamics of the Arctic polar vortex in 2006, 2010 and 2014. In 2006 and 2010, sudden stratospheric warmings were observed: on 21 January 2006, as a result of a significant displacement of the vortex, and on 9 February 2010, as a result of the vortex splitting. During the winter of 2014, the polar vortex was strong and persistent, taking on an elliptical shape in January and February. In the studied years, the breakdown of the Arctic polar vortex occurred in January 2006, February 2010 and March 2014, respectively. Despite the different time periods of the polar vortex breakdown, in each case it was observed after the weakening of the dynamic barrier. A weakening of the dynamic barrier (accompanied by a change in temperature inside the vortex) was observed with a local decrease in wind speed along the vortex edge below 27, 28 and 29 m/s at the 10, 7 and 5 hPa levels, respectively. The polar vortex breakdown occurred simultaneously with or shortly after the decrease in mean wind speed along the vortex edge below 41, 43, and 45 m/s at the 10, 7, and 5 hPa levels, respectively. The weakening of the dynamic barrier in the studied years was often not observed along the entire vertical extent of the polar vortex. In all cases, the weakening and subsequent breakdown of the Arctic polar vortex was first observed in the upper stratosphere and then spread into the middle and lower stratosphere.