Radiation measurements at the Pallas-Sodankyla 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-Sodanlcyld 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 degrees 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 (320-100 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 mu mol 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.