GUV long-term measurements of total ozone column and effective cloud transmittance at three Norwegian sites

Abstract. Measurements of total ozone column and effective cloud transmittance have been performed since 1995 at the three Norwegian sites Oslo/Kjeller, Andoya/Tromso and in Ny-Alesund (Svalbard). These sites are a subset of 9 stations included in the Norwegian UV monitoring network, which uses GUV multi-filter instruments and is operated by DSA and NILU. The network includes unique data sets of high time-resolution measurements that can be used for a for broad range of atmospheric and biological exposure studies. Comparison of the 25-year records of GUV (global sky) total ozone measurements with Brewer direct sun measurements show that the GUVs provide valuable supplements to the more standardized ground-based instruments. The GUVs can fill in missing data and extend the measuring season at sites with reduced staff and/or characterized by harsh environmental conditions, such as Ny-Alesund. Also, a harmonized GUV can easily be moved to more remote/unmanned locations and provide independent total ozone column datasets. The GUV in Ny-Alesund captured well the Arctic ozone hole in March/April 2020, whereas the GUV in Oslo recorded a mini ozone hole in December 2019 with total ozone values below 200 DU. For all the three Norwegian stations there is a slight increase in total ozone from 1995 until today. Measurements of GUV effective cloud transmittance in Ny-Alesund indicate that there has been a significant change in albedo during the past 25 years, most likely resulting from increased temperatures and Arctic ice melt in the area surrounding Svalbard.