Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 1 2008 10.5194/acpd-8-4155-2008 http://www.atmos-chem-phys-discuss.net/8/4155/2008/ http://www.atmos-chem-phys-discuss.net/8/4155/2008/acpd-8-4155-2008.html http://www.atmos-chem-phys-discuss.net/8/4155/2008/acpd-8-4155-2008.pdf 4155 4198 2008-02-29 UV albedo of arctic snow in spring O. Meinander outi.meinander@fmi.fi A. Kontu K. Lakkala A. Heikkilä L. Ylianttila M. Toikka Finnish Meteorological Institute, P.O. BOX 503, 00101 Helsinki, Finland Radiation and Nuclear Safety Authority, P.O. Box 14, 00881, Helsinki, Finland Toikka Engineering Ltd., Hannuntie 18, 02360 Espoo, Finland The relevance of snow for climate studies is based on its physical properties, such as high surface reflectivity. Surface ultraviolet (UV) albedo is an essential parameter for various applications based on radiative transfer modeling. Here, new continuous measurements of the local UV albedo of natural Arctic snow were made at Sodankylä (67.37° N, 26.63° E, 179 m a.s.l.) during the spring of 2007. The data were logged at 1-min intervals. 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. The midday erythemally weighted UV albedo ranged from 0.6 to 0.8 in the accumulation period and 0.5–0.7 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 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 indicating a change in the properties of the snow. Independent UV albedo results with two different types of instruments confirm these findings. The measured temperature of the snow surface was below 0°C on the following mornings. 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