Ozon Hole

Ozone update

The 2007 Antarctic ozone hole

Very low ozone values were again observed over the Antarctic in the austral winter of 2007. Vertical soundings over the South Pole during September and October 2007 showed near-complete destruction of ozone at altitudes between 13 and 21 km. Lower stratosphere temperatures in the winter of 2007 over the Antarctic region were near average levels. Accordingly, the peak size of the ozone hole was smaller than seen during some years of the past decade. Indeed, the size and depth of the Antarctic ozone hole will for the next couple of decades depend mainly on the meteorological conditions inside the south polar vortex.

Low temperatures in the Arctic stratosphere during 2007-2008

The Arctic polar stratosphere cooled down as usual in November/December 2007 as the Arctic vortex grew in strength. By mid-December temperatures at 10 hPa were below those necessary for Polar Stratospheric Clouds to form, an unusual occurrence at such high altitudes—the observed temperatures were among the lowest in the 50-
year record. At lower altitudes the temperatures were not so unusual though they were slightly below average. The temperature for formation of polar stratospheric clouds (PSCs) was reached at the start of December and the minimum temperatures inside the vortex remained low until late February. PSCs were indeed observed above several ground stations in the Arctic.

On 20 January 2008, low temperatures in
the stratosphere over Scandinavia and
a strong westerly wind field led to the
formation of so-called mother-of-pearl
clouds, a special kind of iridescent cloud.
The colours are caused by diffraction
around the small ice particles in the
 cloud.

The photo above shows PSCs observed above Oslo Airport, Norway, on 20 January 2008. The period with PSC conditions ended with a major warming in late February. The accumulated volume of PSCs was large and currently stands as the fourth highest on record. The winter was generally consistent with the tendency of winters to become
colder in recent years, although overall the average stratospheric temperatures over the Arctic have remained the same or even warmed. In other words, it appears that the range (variability) of the observed temperatures has increased. The reasons for this are not yet clear and scientists taking part in the SCOUT-O3 project funded by the European Commission are investigating the possibility of a link to climate change. Preliminary analysis carried out by SCOUT-O3 scientists indicate a loss of 20 per cent in the total ozone column inside the Arctic vortex. More information on the SCOUT-O3 project can be found at: http://www.ozone-sec.ch.cam.ac.uk/scout_o3/.

Source : World Climate News No. 33 | June 2008  by WMO