Spectral UV measurements over Europe within the Second European Stratospheric Arctic and Midlatitude Experiment activities

In the frame of the Second European Stratospheric Arctic and Midlatitude Experiment an intensive program of spectral measurements of global solar UV radiation was organized at several European sites, extending from middle latitudes to the Arctic Circle, in March 1995. Before starting the intensive measurements, a 2-day intercomparison was performed at each site with a traveling spectrophotometer to ensure consistency and comparability between the instruments and their measurements during the period of the study. The collected data were used to investigate the variability of solar ultraviolet irradiances at high and middle latitudes during a period of considerably varying ozone levels. The ratio of the UV erythemal irradiance to UVA irradiance was used to exclude the interference of clouds and other wavelength independent factors. Finally, a simple statistical analysis of the data showed that the variability of UV erythemal dose due to clouds can be at least of similar importance to that induced by the variability of total ozone.