In research projects carried out by the Helmholtz-Gemeinschaft (Helmholtz Association) model simulations are used to predict future developments and changes in the ozone layer. Balloon-borne measurements also provide a data basis.

The ozone layer is an important component of the atmosphere and thus of the global climate system. It is located in the stratosphere at altitudes of about 15 to 30 km. The absorption of solar ultraviolet (UV) radiation in the ozone layer on the one hand protects the biosphere from these harmful high-energy rays and on the other hand acts as an effective heating of the stratosphere. Changes in the ozone distribution in the stratosphere therefore have direct effects not only on the intensity of UV irradiation of the Earth’s surface but also on the thermal structure of the stratosphere and thus on the global climate system. At the same time, changes in atmospheric circulation and the emission of anthropogenic substances impact the ozone layer. It is thus an integral part of the global climate system, and a detailed understanding of the processes which regulate the distribution of ozone in the atmosphere is fundamental for correct climate prediction and the prediction of future UV load on the biosphere.

For about 50 years the emission of chlorinated and brominated substances (in particular hydrochlo­rofluorocarbons and halons) due to human activity has resulted in a thinning of the ozone layer. The ozone loss is very low in the tropics and is today roughly 3.5% on a global average. By far the largest ozone loss has occurred every year since about 1980 in the austral spring, during which time roughly two-thirds of the entire ozone column above the Antarctic are lost. This severe ozone depletion is referred to as the “ozone hole”.

Arctic: ozone depletion above all in winter and spring

Today, ozone depletion likewise occurs in most years in late winter and spring above the Arctic. The variation is from year to year greater than in the Antarctic, but the maximum ozone depletion is as a rule lower [link to text Rex: Ozone Layer in the Polar Regions]. The largest amount of ozone depletion in the Arctic to date occurred in the winter of 2010/2011 (Manney et al. 2011), during which time the ozone losses reached the values usually observed in the Antarctic (Fig. 1).

Measurements of the stratospheric ozone concentration are decisive for monitoring the condition of the ozone layer and for a better quantification of the chemical and physical processes which deter­mine the stratospheric ozone concentration. Figure 2 shows a time series of the minimum level of the ozone column above the Arctic polar cap in March. The large variability of the values from year to year and the record loss in 2011 can be clearly seen. The Alfred-Wegener-Institut (AWI) has been carrying out balloon-borne measurements of the ozone layer in Ny-Ålesund on Spitzbergen and at the Neumayer Station in the Antarctic for a long time [link to text Rex: Chemical Ozone Losses].

Model simulations of the chemical and physical processes in the ozone layer in the stratosphere have become an important component of climate research. Within ESKP the models CLaMS and ATLAS are used by the Helmholtz-Gemeinschaft in order to analyse processes and make limited predictions together with the different Helmholtz centres using measurements. To predict the future development of the ozone layer in a changing climate, extensive, numerically very complex models are required (so-called chemistry-climate models or Earth system modules). In particularly cold future Arctic winters, for example 2011, there exists the danger of a strong thinning of the ozone layer above densely populated areas in spring.

G. Bernhard, G. Manney, V. Fioletov, J.-U. Grooß, A. Heikkilä, B. Johnsen, T. Koskela, K.   Lakkala, R. Müller, C. L. Myhre, M. Rex (2012) [The Arctic] Ozone and UV radiation [in “State of the Climate in 2011”]. Bull. Amer. Meteor. Soc., 93 (7), S129-S132Manney, G. L., M. L. Santee, M. Rex, N. J. Livesey, M. C. Pitts, P. Veefkind, E. R. Nash, I. Wohltmann, R. Lehmann, L. Froidevaux, L. R. Poole, M. R. Schoeberl, D. P. Haffner, J. Davies, V. Dorokhov, H. Gernandt, B. Johnson, R. Kivi, E. Kyrö, N. Larsen, P. F. Levelt, A. Makshtas, C. T. McElroy, H. Nakajima, M. C. Parrondo, D. W. Tarasick, P. von der Gathen, K. A. Walker, N. S. Zinoviev, Unprecedented Arctic ozone loss in 2011, (2011), Nature, 478, 7370, 469.

R. Müller, J.-U. Grooß, C. Lemmen, D. Heinze, M. Dameris, G. Bodeker (2008) Simple measures of ozone depletion in the polar stratosphere, 8, Atmos. Chem. Phys., 251–264.