• Gunther Seckmeyer, Darius Pissulla, Merle Glandorf, Diamantino Henriques, Bjorn Johnsen, Ann Webb, Anna-Maria Siani, Alkis Bais, Berit Kjeldstad, Colette Brogniez, Jacqueline Lenoble, Brian Gardiner, Peter Kirsch, Tapani Koskela, Jussi Kaurola, Beate Uhlmann, Harry Slaper, Peter den Outer, Michal Janouch, Peter Werle, Julian Gröbner, Bernhard Mayer, Alain de la Casiniere, Stana Simic, and Fernanda Carvalho.
• Institute of Meteorology and Climatology, Leibniz University of Hannover, Hannover, Germany. seckmeyer@muk.uni-hannover.de
• Photochem. Photobiol. 2008 Jan 1; 84 (1): 172-9.

AbstractThe diurnal and annual variability of solar UV radiation in Europe is described for different latitudes, seasons and different biologic weighting functions. For the description of this variability under cloudless skies the widely used one-dimensional version of the radiative transfer model UVSPEC is used. We reconfirm that the major factor influencing the diurnal and annual variability of UV irradiance is solar elevation. While ozone is a strong absorber of UV radiation its effect is relatively constant when compared with the temporal variability of clouds. We show the significant role that clouds play in modifying the UV climate by analyzing erythemal irradiance measurements from 28 stations in Europe in summer. On average, the daily erythemal dose under cloudless skies varies between 2.2 kJ m(-2) at 70 degrees N and 5.2 kJ m(-2) at 35 degrees N, whereas these values are reduced to 1.5-4.5 kJ m(-2) if clouds are included. Thus clouds significantly reduce the monthly UV irradiation, with the smallest reductions, on average, at lower latitudes, which corresponds to the fact that it is often cloudless in the Mediterranean area in summer.

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