This year’s Antarctic ozone hole was smaller than in recent years, both in terms of area and depth, according to WMO’s Antarctic Ozone Bulletin. Using information gathered from the ground, from weather balloons and from satellites, the Bulletin said that the ozone hole area reached zero on 10
November – earlier than in recent years.
The reason for the weak ozone hole this year is twofold:
Firstly, relatively warm temperatures in the stratosphere (around 20 km altitude) limited the formation of polar stratospheric clouds which, through a chemical chain reaction between water, nitric acid and halogenated reservoir gases cause ozone loss. In this respect, the 2012 ozone hole was similar to the one in 2010, when a sudden stratospheric warming in July/August gave rise to a smaller amount of polar stratospheric clouds than usual.
Secondly, the polar vortex - a large low-pressure system where high speed winds (polar jet) in the stratosphere circle the Antarctic continent – was also relatively perturbed and this led to ozone rich air being transported in from lower latitudes. This transport of ozone rich air affected in particular the stratosphere at around 25 km altitude, which is above the region where most of the ozone loss takes place, which is typically in the 14-20 km height range. Ozone loss in the 14-20 km region took place at nearly the same extent as in recent