Why is the Arctic ozone hole usually less severe than the Antarctic ozone hole?

The Arctic ozone hole is generally less severe than the Antarctic ozone hole primarily because the polar vortex in the Northern Hemisphere is neither as strong nor as cold as the one that forms over Antarctica.1

The severity of ozone depletion is closely linked to the formation of polar stratospheric clouds (PSCs), which provide the surface for chemical reactions that convert chlorine into ozone-destroying forms. In the Antarctic, the polar vortex is highly stable and isolated due to the continent's geography—being surrounded by ocean rather than a mix of land and water—which minimizes the influence of mountain ranges and land-ocean temperature contrasts that would otherwise disrupt the vortex.12

Conversely, the Arctic polar vortex is frequently disrupted by Rossby waves caused by land-ocean temperature differences and mountain ranges. These disruptions allow warmer air to mix into the region, preventing the sustained, extremely cold temperatures required for PSCs to persist long enough to cause the extensive ozone destruction observed in the Antarctic.21