Radiation measurements at the Pallas-Sodankylä Global Atmosphere Watch station — diurnal and seasonal cycles of ultraviolet, global and photosynthetically-active radiation

We present time series of solar ultraviolet radiation (UVR), global radiation, and photosynthetically-active radiation (PAR) measurements from the Pallas-Sodankyla Global Atmosphere Watch (GAW) station at Sodankyla for the period 1990–2013. Measurements were performed both in an open area and in the surrounding boreal forest, which had a total leaf area index of 3.6. We present a method to homogenize multifilter radiometer UV time series. Using this method, the relative mean differences between the multifilter radiometer and the reference spectroradiometer were 5% for UVB and erythemally-weighted dose rates, for all sky conditions and solar zenith angles (SZA) smaller than 60° during the period 2008–2012. Our results show that daily doses measured in the forest were four times smaller than those measured in the nearby open area. Maximum UVB (280–320 nm) and UVA (320–400 nm) daily doses of 75.0 kJ m–2 and 1.74 MJ m–2, respectively, were measured during the period of multifilter radiometer measurements, 2002–2012. The maximum daily sum of global radiation during the years 2000–2010 was 31.4 MJ m–2, measured in 2010. The maximum PAR during 2000–2012 was 1830 μmol m–2 s–1, measured in 2000. For the entire period of spectral UV measurements, 1990–2013, a maximum UV index of 6 was measured in 2011 and 2013.