| Summary: | Measurements of broadband UVA and erythemal UVB solar radiation are carried out at Jungfraujoch High Alpine Research Station (3576 m a.s.l., Switzerland) and in Innsbruck (577 m a.s.l., Austria) since 1981. Under clear sky conditions, the altitude effect of daily totals of global (direct and diffuse) radiation results in 9 ± 2 %/1000 m (UVA) respectively 18 ± 2 %/1000 m (UVB) in summer and in 11 ± 5 %/1000 m (UVA) and 23 ± 6 %/1000 m (UVB) in winter. This measured altitude dependence is compared with the calculated altitude effect obtained by application of Green's radiation model. This model allows the calculation of spectral UV intensities as a function of solar elevation, ozone amount, turbidity, altitude a.s.l., and albedo. A seasonal variation of the altitude effect of daily totals is caused by alterations of solar elevations, albedo, and turbidity within the year. Thus, no generally applicable number can be given for the altitude effect. The range of the calculated altitude effect is 9 to 24 %/1000 m (broadband UVA) and 13 to 36 %/1000 m (erythemal UVB). The measured altitude effect is approximately in agreement with Green's radiation model, applying standard model conditions.
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