Surface albedo measurements over Antarctic sites in summer

Abstract

[1] Surface albedo data from several Antarctic sites were compared to determine spatial and temporal variability in albedo. The highest degree of variability was observed at Hells Gate Station on the Ross Sea coast. The temperature close to the melting point and the reduced katabatic winds during summer allowed a strong metamorphism of the snow. At Neumayer, a coastal station by the Weddell Sea, snowfall and drifting snow were more frequent, and the surface albedo was constantly high. The albedo increased by an average of 0.07 from clear days to days with snowfall and overcast sky. Surprisingly, the hourly variation in albedo at Hells Gate Station showed a trend similar to the one observed at Neumayer Station and at Dome Concordia Station on the high plateau, when only those days with fresh snow at the surface were considered. The albedo steadily decreased during the day for solar zenith angles less than 80°. Snow metamorphism, sublimation during the day, and refreezing and/or crystal formation/precipitation during the night can explain the observed trend. To represent the daily trend in albedo over ice and fresh snow, we propose two parameterizations, which can be easily applied over other Arctic and Antarctic sites in summer. Small-and large-scale surface roughness elements can result in distortion in the measured albedo. The data at Reeves Névé Station show the effect produced on the albedo by changing slightly the sampling area immediately over a sastruga.

Albedo over rough snow and ice surfaces

“…Consequently, several studies have assessed the spatiotemporal variations in surface albedo using ground-based measurements (e.g., Arendt, 1999;Brock, 2004;Brock et al, 2000;Pirazzini, 2004), albedo data derived from satellite data (Dumont et al, 2012;Klok et al, 2003;Stroeve et al, 2006) or terrestrial photography (Corripio, 2004;Dumont et al, 2011).…”

“…One decisive factor for the representativeness is the "macroscopic" roughness of the surface, which has a strong effect on the surface albedo (Warren et al, 1998;Zhuravleva and Kokhanovsky, 2011). Although this effect has been extensively quantified over sastrugis and crevasses (Hudson and Warren, 2007;Kuchiki et al, 2011;Leroux and Fily, 1998;Pfeffer and Bretherton, 1987;Warren et al, 1998), its effect over penitentes (spike formations of snow and ice up to several meters high; Lliboutry, 1953), typical of several high altitude mountain glaciers and snow fields, remains less understood and limited to individual measurements. For example, Corripio and Purves (2005) and Kotlyakov and Lebedeva (1974) noted albedo reductions of 8-10 % over penitentes.…”

“…Secondly, multiple reflections between the walls cause light trapping in the trough. In this framework Pfeffer and Bretherton (1987) define the effective albedo that differs from the flat surface albedo (i.e., albedo of a flat surface with identical surface material properties and illumination conditions) due to light trapping within crevasses, whereas the flat surface albedo differs from the material albedo (i.e., albedo when the incident radiation has a incidence angle of 0 • ) due to changes in the zenith angle of incoming radiation. The concept of effective albedo is useful as it combines both the surface properties of the material and the light trapping due to multiple reflections.…”

“…The concept of effective albedo is useful as it combines both the surface properties of the material and the light trapping due to multiple reflections. Pfeffer and Bretherton (1987) developed a radiative transfer model to simulate that, depending on the opening angle, crevasses reduce the effective albedo up to 0.4. Furthermore, they show that the opening angle of the crevasse determines the differences between effective albedo and flat surface albedo as smaller opening angles (i.e., steeper walls) result in stronger albedo reductions.…”

“…Although the use of radiative transfer models (Cathles et al, 2011(Cathles et al, , 2014Fortuniak, 2007;Helbig et al, 2009;Pfeffer and Bretherton, 1987) allows quantifying the effect of surface topography on effective albedo, their use in energy balance models remains limited (e.g., Corripio and Purves, 2005) as the exact rough topography often remains unknown. Instead albedo measurements derived from hemispherical shortwave radiation sensors or remote sensing data are typically used as effective albedos in the energy balance models (Corripio and Purves, 2005;Pellicciotti et al, 2008;Winkler et al, 2009).…”