Warmer stratosphere, active polar vortex help speed seasonal recovery
By Summit Voice
FRISCO — Relatively warm stratospheric temperatures helped limit the size of this year’s Antarctic ozone hole, which disappeared completely by Nov. 10, earlier than in recent years.
Using data gathered from ground stations and weather balloons, the World Meteorological Organization said the warmer temps at an elevation of about 20 kilometers 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 and August gave rise to a smaller amount of polar stratospheric clouds than usual.
The WMO also said 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.
The transport of ozone rich air was particularly noticable in the stratosphere at around 25 km altitude, 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 years.
During the first half of August, the area increased more slowly than at the same time in many the recent years. Starting in mid-August, the increase was similar to 2011. From early September, the ozone hole area leveled off but increased a bit again after the middle of September. Starting early October, the ozone hole area dropped rapidly.
The Antarctic ozone hole is an annually recurring winter and spring phenomenon resulting from extremely low temperatures in the stratosphere and the presence of ozone-depleting substances. It typically reaches its maximum surface area during the second half of September and the maximum depth during the first half of October.
Despite a 25-year-old agreement that limits the production and use of ozone-destroying chemicals (the Montreal Protocol), stratospheric ozone in the Arctic and Antarctic regions, as well as globally, is no longer decreasing, but it has not yet started to recover either.
Ozone-destroying hemicals such as chorolflouorocarbons and halons have a long atmospheric lifetime, illustrating the delicate balance of the atmospheric system, which is currently being overloaded with heat-trapping greenhouse gases.
The ozone layer outside the Polar regions is projected to recover to its pre-1980 levels before the middle of this century. In contrast, the ozone layer over the Antarctic is expected to recover much later.