Variability of spectral solar ultraviolet irradiance in an Alpine environment

Seven spectroradiometers measured simultaneous surface UV irradiances at si x different sites in the vicinity of Garmisch-Partenkirchen, Germany, durin g spring 1999. The measured clear-sky radiance variability between the site s was analyzed with respect to altitude, aerosol optical depth, solar zenit h angle, effective albedo, and tropospheric ozone. For conditions of low ae rosol loading the increase of irradiance per 1000 m altitude difference was 9% at 400 nm, 20% at 320 nm, and 30% at 300 nm in this season. Effective a lbedo differences of 0.15, 0.29, and 0.65 were found between the snow-cover ed stations and the snow-free ground station with the higher effective albe do values determined at the two mountain stations. Clean continental aeroso l with a single-scatter albedo of 0.95 were observed during this campaign. The measurements and the observed variations between the sites should enabl e more accurate modeling studies to be performed for an Alpine environment.