Abstract
Abstract. 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°22'N, 26°39'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 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 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. Hence, the reversible diurnal change, evident for ~1–2 h, could be explained by the daily metamorphosis of the surface of the snowpack, in which the temperature of the surface increases, melting some of the snow to liquid water, after which the surface freezes again.
Highlights
The relevance of snow for climate variability and change is based on its physical properties, such as high surface reflectivity, i.e., albedo (IPCC, 2007)
Surface UV albedo is an essential parameter for various applications based on radiative transfer (RT) modeling, including various satellite retrieval algorithms
On the basis of our experience, the spectral responses of SL501 sensors may change in time, and the responses should be determined on a regular basis, preferably every year or every second year
Summary
The relevance of snow for climate variability and change is based on its physical properties, such as high surface reflectivity, i.e., albedo (IPCC, 2007). The albedo of snow may decrease because of anthropogenic soot (Wiscombe and Warren, 1980; Warren and Wiscombe, 1980) and aging and melting (Wiscombe and Warren, 1980; Blumthaler and Ambach, 1988; Wuttke et al, 2006). More radiation is absorbed, and the melting of the snow may increase due to this albedo feedback mechanism (e.g., Bony et al, 2006). The UV albedo for a surface with snow is high, and due to multiple reflections affects downwelling radiation (Bais and Lubin, 2007). Surface UV albedo is an essential parameter for various applications based on radiative transfer (RT) modeling, including various satellite retrieval algorithms. Current satellite UV algorithms demand better information on UV albedo, especially for land when covered by snow (e.g., Arola et al, 2003, Tanskanen and Manninen, 2007)
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