1ST SOUTHERN-HEMISPHERE INTERCOMPARISON OF MEASURED SOLAR UV SPECTRA

Three UV spectroradiometers from the National Institute of Water and Atmospheric Research (NIWA) New Zealand, the Fraunhofer Institute (IFU) Germany, and the Australian Radiation Laboratory (ARL) Australia were intercompared at Lauder NZ on 23 February 1993. Over the spectral range 290-400 nm, the agreement between the IFU and NIWA instruments was better than 5%. At noon on this day, the irradiances measured by all three instruments agreed within +/- 10%, except at wavelengths shorter than 300 nm, where the ARL instrument gave higher readings. At larger solar zenith angles (SZA) the differences at short wavelengths were more pronounced, and at wavelengths above 300 nm the ARL measurements were systematically lower. The reasons for these differences are discussed. Having established the differences between the sets of instrumentation, spectra of maximum clear sky UV irradiances observed by these groups in New Zealand, Australia, and Europe are compared. The erythemally weighted irradiance observed in Melbourne Australia was the highest (0.35 W m-2. Respective maxima for Lauder NZ and for Neuherberg Germany were 85% and 66% of that in Australia. Differences are larger for DNA-weighted UV.