Effects of solar elevation and cloudiness on snow albedo at the South Pole

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Abstract
Upward and downward fluxes of shortwave radiation (0.285 < λ < 2.8 μm) measured at Amundsen‐Scott Station (South Pole) during the summers of 1975, 1976, and 1977 are analyzed to determine effective surface albedos as functions of cloudiness (N) and solar elevation angle (A). For nonovercast conditions (N ≤ 0.25) the albedo decreases linearly from 0.97 at A ≲ 2° to a minimum of 0.83 ± .005 for A ≳ 20°. With near overcast conditions (N ≳ 0.7), linear decrease is also found from 0.93 at A < 2° to 0.84 ± 0.005 for A > 18°. The nonovercast results are compared with albedos reported for other Antarctic plateau stations. The higher values at the South Pole are attributed to slower rates of surface snow metamorphosis there due to lower maximum sun elevations and absence of diurnal radiative flux and temperature cycles. Arguments are presented to resolve conflicting reports that cloudiness both increases and decreases the snow albedo, and our results show that the effect of clouds depends on the solar elevation angle.