Ozone recovery and stratospheric cooling - What can we see from a few long-term stations?
Résumé
Thanks to the Montreal Protocol, the decline of stratospheric ozone has been stopped. Ozone has now started to recover. The Kyoto Protocol, however, has been less successful. CO2 levels keep increasing, the stratosphere keeps cooling. Among other things, this cooling does affect ozone recovery. What can data from just a few NDACC stations tell us about these long-term changes? In our presentation we will look at long-term variations of stratospheric ozone and temperature since the 1960s. We will show results from NDACC stations and from Europe, and will put those into the context of global observations. At Hohenpeissenberg (47.8°N, 11.0°E), ozone in the upper stratosphere (40km / 2hPa) has been increasing since about 2000, by almost 10%. Levels are already comparable to what was measured in the late 1980s. At the same time, temperature has been declining substantially since about 2000, by more than 3 K. Total ozone, where variations are coming mostly from the lower stratosphere, has been increasing since the mid 1990s at Hohenpeissenberg. This increase, and the previous decline, largely track the evolution of Equivalent Effective Stratospheric Chlorine (EESC). Superimposed are natural variations, which were particularily large in 2010 and 2011. 2010 had very large ozone columns, comparable to the early 1980s. 2011, on the other hand, was a year with very low ozone columns, and with unprecedented large ozone losses in Arctic spring. At Hohenpeissenberg, the total ozone annual mean of 2011 was the 3rd lowest on record since 1968. Only 1992 and 1993, after the Pinatubo eruption, had lower ozone columns. Multiple linear regression analysis indicates that this large swing from 2010 to 2011 is connected to meteorological changes, i.e. the change of the Arctic Oscillation from pronounced negative phase in 2010, to pronounced positive phase in 2011.