This year’s Antarctic ozone hole was smaller than in recent years, both in terms of area and depth, according to the World Meteorological Organization’s (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 November 10, 2012 – earlier than in recent years.
The WMO Bulletin which was made available to the Ghana News Agency on Friday, said the reason for the weak ozone hole this year was two-fold.
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.
It said 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.
The Bulletin explained that 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, and that ozone loss in the 14-20 km region took place at nearly the same extent as in recent years.
The Bulletin said during the first half of August, the area increased more slowly than at the same time in many of the recent years. However, from mid August the increase more or less followed the same development as in 2011.
It noted that from early September, the ozone hole area levelled off but increased a bit again after the middle of September and that starting early October the ozone hole area dropped rapidly.
It said the Antarctic ozone hole is an annually recurring winter/spring phenomenon due to the existence of extremely low temperatures in the stratosphere and the presence of ozone-depleting substances.
The Bulletin further indicated that an international agreement known as the Montreal Protocol which was celebrating its 25th anniversary this year, had successfully cut the production and consumption of ozone-destroying chemicals such as chorolflouorocarbons and halons but said that these chemicals had a long atmospheric lifetime.
It held that the ozone layer outside the Polar regions was projected to recover to its pre-1980 levels before the middle of this century, and that in contrast, the ozone layer over the Antarctic was expected to recover much later.
The WMO’s Antarctic Ozone Bulletin monitors the development of the ozone hole in order to inform policymakers about changes in the environment.
“The information comes from WMO’s Global Atmosphere Watch network’s observations from satellites, weather balloons and ground observations from some of the world’s most remote and inhospitable terrains,” the Bulletin explained. GNA