Arctic Snow and Diurnal Changes in Albedo

Local snow albedo on ultraviolet (UVA, UVB, erythemally weighted UV) and visible (VIS) region, at wavelengths of photosynthetically active radiation (PAR, 400-700 nm), has been measured in at Sodankylä (67 o N, 26 o E, 179 m a.s.l.) during the spring of 2007. SL501 and NILU-UV radiometers at 2 m height were used. The data were logged at 1-min intervals. The measurement period covered accumulation and melting of snow. The accumulation of snow was up to 68 cm. The surface layer thickness varied from 0.5 to 35 cm with the snow grain size between 0.2 and 2.5 mm. According to SL501 results, the midday erythemally weighted UV albedo ranged from 0.6 to 0.8 in the accumulation period, and from 0.5 to 0.7 during melting. During the snow melt period, under cases of an almost clear sky and variable cloudiness, an unexpected diurnal decrease of 0.05 in erythemal albedo soon after midday, and recovery thereafter, was detected. This diurnal decrease in albedo was found to be asymmetric with respect to solar midday, thus possibly indicating a change in the properties of the snow. Independent NILU-UV results on UVA and UVB confirm these findings. In addition, in some cases diurnal asymmetry in albedo (with or without diurnal decrease and recovery) was observed. The results are discussed in context of corresponding Antarctic results, too.