Measurements of Diurnal Variations in Snow Albedo on Lemon Creek Glacier, Alaska

Abstract

Two Eppley pyrheliometers were used to measure incoming and reflected sun and sky radiation over a saturated, melting snowpack. Albedo values computed from these measurements varied strongly, not only with snow surface conditions, but also diurnally with the angle of the sun, and from clear to cloudy skies. On clear days minimum albedo in the afternoon was approximately 35 per cent less than the maximum in early morning; a secondary maximum occurred at sunset. Also, midday albedos were higher under cloudy skies than under clear skies. These variations appear to relate primarily to changes in angle of incident radiation, and secondarily to changes in the physical structure of the snow surface. Spectral changes in incident radiation are also a possible factor.

The Diurnal Hysteresis of Snow Albedo

“…Several authors have reported the fact that snow albedo may exhibit hysteresis; the albedo in the morning being higher than in the afternoon for identical solar elevation (e.g. Hubley, 1955). We consider here several different reports of this effect and present some previously unpublished results.…”

The interpretation of albedo measurements on a snowcovered slope

“…These effects are coupled to the surface temperature and the energy budget and have therefore a phase lag with respect to solar elevation [2,3 ]. Errors in measurement, increasing with the lower energy available at low sun elevation and lacking corrections for the deviation from exact "cosine-law" response of the sensors can produce further falsification of measured albedo.…”

Problems of determining snow albedo for the high arctic: Research note

“…Albedo has commonly been reported to vary inversely with solar elevation on clear days (Barkstrom, 1972;Hubley, 1955;Langleben, 1968;Nkemdirim 1972). This daily cycle for snow may be caused by the variation in the specular reflection component with sun angle, snow metamorphism during the day or instrumental error, particularly a deviation of the pyranometer response from the cosine law (Dirmhirn and Eaton, 1975).…”