COMPARISON OF MODELS USED FOR UV INDEX CALCULATIONS

Eighteen radiative transfer models in use for calculation of UV index are compared with respect to their results for more than 100 cloud-fre e atmospheres, which describe present, possible future and extreme con ditions. The comparison includes six multiple-scattering spectral mode ls, eight fast spectral models and four empirical models. Averages of the results of the six participating multiple-scattering spectral mode ls are taken as a basis for assessment. The agreement among the multip le-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 r esults of the empirical models agree reasonably well with the referenc e models but only for the atmospheres for which they have been develop ed. The data to describe the atmospheric conditions, which are used fo r the comparison, together with the individual results of all particip ating models and model descriptions are available on the Internet: /ww w.meteo.physik.uni-muenchen.de/strahlung/cost/.