2011-09-12: Climate science: Explaining Antarctic ozone hole anomalies

The strongly reduced Antarctic stratospheric ozone hole destruction in 2010 and several other recent years, results from the occurrence of dramatic meteorological events in the polar winter known as sudden stratospheric warmings (SSWs).
These findings are reported in a paper published in Scientific Reports, a new online and open access publication of the Nature Publishing Group.
The annual occurrence of the Antarctic ozone hole is related to the gradual increase in atmospheric concentrations of chlorine, resulting from the anthropogenic production of chlorofluorocarbons (CFCs). International efforts to reduce these emissions have led to a gradual decline of these substances but despite these changes, in several years since 1979 - 1986, 1988, 2002, 2004 and 2010 - there have been unexpectedly small amounts of ozone depletion, mainly at around 20-25 km altitude (in the middle stratosphere). ). Although it has long been known that such events are related to differences in the way the meteorology around Antarctica behaves from year to year, the mechanisms linking such variations with ozone depletion have remained unclear.

Based on satellite observations and measurements from the Microwave Limb Sounder instrument, Jos de Laat and Michiel van Weele report that the reduced ozone destruction at 20-25 km altitude in 2010 is related to the occurrence of a mid-winter minor Antarctic SSW. Although the SSW raised stratospheric temperatures by only a few Kelvins, it causes humidity rich air in the middle stratosphere to descend (although not below 20 km), which in turn modified the air's chemical composition which resulted in significantly less effective ozone destruction between 20-25 km altitude. This process did not effect the stratospheric composition further down below between 15-20 km, and in 2010 ozone destruction at those altitudes was therefore similar to other years. The years since 1979 with similarly low amounts of ozone depletion are all characterized by either minor or major SSWs, further highlighting the importance of these meteorological events in stratospheric ozone hole destruction.

For 2011, based on the findings this paper in combination with observations of the development of the Antarctic ozone hole in 2011 no unusual behavior of the Antarctic ozone hole is expected (as of Monday 5 September 2011).

de Laat, A.T.J. & van Weele, M. The 2010 Antarctic ozone hole: Observed reduction in ozone destruction by minor sudden stratospheric warmings. Sci. Rep. 1, 38; DOI:10.1038/srep00038 (2011).

The article can be found here.
Antarctic ozone mass deficit for the years 1979-2010 for three different “ozone destruction” definitions: D1 is the average for the period 21 to 30 September, D2 is the period 7 September to 13 October and D3 denotes the “worst” 30-day period, i.e. the largest deficit for any 30-day period. The ozone mass deficit is given in 109 kg ozone with regard to the 220 Dobson Unit total ozone column value (Dobson Unit = DU = 2.69 1016 molecules/cm2) for total ozone columns south of 45°S. The vortex area is the total area where total ozone columns south of 45°S are smaller than 220 DU. For 1979-2008 MSR data is used, for 2009 and 2010 SCIAMACHY total ozone column assimilation data is used. Arrows indicate years with anomalously low ozone mass deficits.