Erythemal UV observations at Belsk, Poland, in the period 1976–2008: Data homogenization, climatology, and trends

Measurements of erythemal irradiance have been carried out continuously at Belsk since May 1975. We present a homogenization procedure of the UV time series for the period of 1976-2008. Long-term oscillations discovered in the homogenized data set agree with those extracted from the reconstructed UV data for all-sky and clear-sky conditions. The UV climatology was established and the UV variability was determined. Positive UV trends were found for the period of 1976-2008 in the annual mean (5.6±0.9% per decade), in the seasonal mean for the warm subperiod of the year (April-October, 5.5±1.0% per decade), and in monthly means (˜2-9% per decade). A satisfactory agreement between the trend extracted from the homogenized ground-based data and that found in satellite UV data for Belsk (1979-2008) supports the reliability of satellite trend analyses over wider areas during snowless periods.