Comparison of Models Used for UV Index Calculations

Peter Koepke*¹, Alkiviadis Bais², Dimitrios Balis², Michael Buchwitz³, Hugo De Backer⁴, Xavier de Cabo⁵, Pierre Eckert⁶, Paul Eriksen⁷, Didier Gillotay⁸, Anu Heikkilä⁹, Tapani Koskela⁹, Bozena Lapeta¹⁰, Zenobia Litynska¹⁰, Jeronimo Lorente⁵, Bernhard Mayer¹¹, Anne Renaud¹², Ansgar Ruggaber¹, Günther Schauberger¹³, Gunther Seckmeyer¹¹, Peter Seifert¹, Alois Schmalwieser¹³, Harry Schwander¹, Karel Vanicek¹⁴ and Mark Weber³

*To whom correspondence should be addressed at: Meteorol. Inst., Theresienstr. 37, D-80333 Muenchen, Germany. Fax: ++49 89 23944381; e-mail: peter.koepke@lrz.uni-muenchen.de

ABSTRACT

Eighteen radiative transfer models in use for calculation of UV index are compared with respect to their results for more than 100 cloud-free atmospheres, which describe present, possible future and extreme conditions. The comparison includes six multiple-scattering spectral models, eight fast spectral models and four empirical models. Averages of the results of the six participating multiple-scattering spectral models are taken as a basis for assessment. The agreement among the multiple-scattering models is within +/-0.5 UV index values for more than 80% of chosen atmospheric parameters. The fast spectral models have very different agreement, between +/-1 and up to 12 UV index values. The results of the empirical models agree reasonably well with the reference models but only for the atmospheres for which they have been developed. The data to describe the atmospheric conditions, which are used for the comparison, together with the individual results of all participating models and model descriptions are available on the Internet: http://www.meteo.physik.uni-muenchen.de/strahlung/cost/.