The impact of snow specific surface area and clouds on snow albedo - Investigations made at Kohnen Station, Antarctica, during summer 2013/2014

Johannes.Freitag [ at ]


Albedo is known to be one of the most important factors determining near-surface polar energy fluxes in Polar Regions and is therefore a key component in both global and regional climate models. Albedo is, however, highly variable and it is of great interest to incorporate albedo variability into models for reliable prognoses. Instead of assuming constant albedo values, this is achieved by incorporating albedo parameterizations into models. To understand the processes that influence albedo is therefore crucial. As the albedo is determined by the scattering of incoming radiation within the upper cm of snow the link between surface albedo and snow grain size is studied. During the austral summer of 2013/2014 a field campaign was conducted at Kohnen Station (75° 00’ S, 0° 04’E) in which broadband albedo and Specific Surface Area (SSA), as a measure of grain size, were investigated simultaneously for the first time for December and January in Antarctica. Kohnen Station is located on the East Antarctic Plateau and is characterized by low precipitation. In this work four data sets gained during the campaign were analyzed: 1) broadband albedo, 2) SSA, 3) synoptic observations (clouds and precipitation), 4) images of the snow surface. It was found that the two main influencing factors on seasonal albedo development are clouds in the lowest cloud layer and variations in SSA. Overcast conditions, defined by 100 % clouds in the lowest cloud layer result in an albedo increase of around 3%. A similar albedo increase is provoked when SSA increases by 18 m2/kg. During the austral summer 2013/2014 SSA increases in this order of magnitude were observed after precipitation events. Besides clouds and SSA, albedo is influenced by the solar zenith angle(SZA). Clear sky diurnal albedo decreased during the morning and evening hours although increasing SZA have a contrary effect. An explanation for this bias is that an increase in shade on the snow surface may result in an albedo decrease for low SZA. A first attempt was made to extract shade amounts from surface images and it was found that increasing shade amount correlate well with decreasing clear sky albedo. Based on the outcomes of this study it can be concluded that the crucial factors to include into albedo parameterizations for the East Antarctic Plateau are SSA and cloud amount.

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Belke Brea, M. (2015): The impact of snow specific surface area and clouds on snow albedo - Investigations made at Kohnen Station, Antarctica, during summer 2013/2014 , Master thesis, University of Bremen.

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