Spectral albedo of seasonal snow during intensive melt period at Sodankylä, beyond the Arctic Circle

We have measured spectral albedo, as well as ancillary parameters, of seasonal European Arctic snow at Sodankyla, Finland (67 degrees 22' N, 26 degrees 39' E). The springtime intensive melt period was observed during the Snow Reflectance Transition Experiment (SNORTEX) in April 2009. The up-welling and downwelling spectral irradiance, measured at 290-550 nm with a double monochromator spectroradiometer, revealed albedo values of similar to 0.5-0.7 for the ultraviolet and visible range, both under clear sky and variable cloudiness. During the most intensive snowmelt period of four days, albedo decreased from 0.65 to 0.45 at 330 nm, and from 0.72 to 0.53 at 450 nm. In the literature, the UV and VIS albedo for clean snow are similar to 0.97-0.99, consistent with the extremely small absorption coefficient of ice in this spectral region. Our low albedo values were supported by two independent simultaneous broadband albedo measurements, and simulated albedo data. We explain the low albedo values to be due to (i) large snow grain sizes up to similar to 3 mm in diameter; (ii) meltwater surrounding the grains and increasing the effective grain size; (iii) absorption caused by impurities in the snow, with concentration of elemental carbon (black carbon) in snow of 87 ppb, and organic carbon 2894 ppb, at the time of albedo measurements. The high concentrations of carbon, detected by the thermal-optical method, were due to air masses originating from the Kola Peninsula, Russia, where mining and refining industries are located.