Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 1 2008 10.5194/acpd-8-3357-2008 http://www.atmos-chem-phys-discuss.net/8/3357/2008/ http://www.atmos-chem-phys-discuss.net/8/3357/2008/acpd-8-3357-2008.html http://www.atmos-chem-phys-discuss.net/8/3357/2008/acpd-8-3357-2008.pdf 3357 3381 2008-02-18 Modelling UV irradiances on arbitrarily oriented surfaces: effects of sky obstructions M. Hess P. Koepke Peter.Koepke@lmu.de Meteorological Institute of the L.-M. University, Munich, Germany A method is presented to calculate UV irradiances on inclined surfaces that additionally takes into account the influence of sky obstructions caused by obstacles such as mountains, houses, trees, or umbrellas. Thus the method allows calculating the impact of UV radiation on biological systems, such as for instance the human skin or eye, in any natural or artificial environment. The method, a combination of radiation models, is explained and the correctness of its results is demonstrated. The effect of a natural skyline is shown for an Alpine ski area, where the UV irradiance even on a horizontal surface may increase due to reflection at snow by more than 10%. In contrast in a street canyon the irradiance on a horizontal surface is reduced down to 30% in shadow and to about 75% for a position in the sun. Arola A., et al.: Assessment of four methods to estimate surface UV radiation using satellite data, by comparison with ground measurements from four stations in Europe, J. Geophys. Res., 107(D16), 4333, doi:10.1029/2001JD000462, 2002. Bais, A., Lubin, D., Arola, A., Bernhard, G., Blumthaler, M., Chubarova, N., Erlick, C., Gies, H. P., Krotkov, N., Lantz, K., Mayer, B., McKenzie, R. L., Piacentini, R.D., Seckmeyer, G., Slusser, J. R., and Zerefos, C. 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