Polar ozone depletion in the Arctic happens when the polar vortex weakens or splits in early winter, leading to less destruction of ozone from late winter to spring. This weakening or splitting causes polar stratospheric clouds to melt, preventing ozone destruction even when the polar vortex is strong. The study used data from ERA-Interim reanalysis and NASA satellite data to show the importance of polar vortex strength in preventing ozone depletion.