Modelling the depletion of ozone in the stratosphere
The hole in the stratospheric ozone layer over the Antarctic has attracted a great deal of attention. What is less known is that alarming levels of ozone depletion also occur over the Arctic. In both cases, the increased levels of ultraviolet radiation penetrating through to the Earth's surface pose a serious threat. Scientists tackling this problem aim to increase our understanding of the complex atmospheric chemistry and physics at work in the destruction of ozone at both poles. The European Commission is doing its part to support their efforts. The TOPOZ-III project, funded through the EESD Programme, evaluated the ability of several Chemical Transport Models (CTMs) to correctly predict the annual evolution of ozone concentrations. Four CTMs were tested: ClaMS, KASIMA, REPROBUS and SLIMCAT. Two unusual test cases were selected in order to assess the robustness of the models. The first was the split of the polar vortex (and ozone hole) over the Antarctic in September 2002, the result of a sudden warming of the stratosphere. All four models were able to successfully reproduce this exceptional event. The two models (KASIMA and REPROBUS) employing pressure as the vertical coordinate (as opposed to potential temperature) showed better ability to model the methane cycle. Methane is important because the by-products of its chemical decomposition in the stratosphere contribute to ozone destruction. The second test case addressed the ozone layer over the Arctic during the winter of 2002-2003. Again, all four CTMs produced a reliable reconstruction of the lifecycle of the polar vortex, which is responsible for accelerated ozone destruction. These encouraging results instil confidence in the ability of these models to properly predict future ozone concentrations. More detailed information, including copies of public project reports, can be found at the TOPOZ-III web site: http://www-imk.fzk.de/topoz-iii/
