The Albedo Decay of Prairie Snows

Abstract

Daily albedos of snow were measured between November and April, 1969?87, and were analyzed to determine the decay rate between snowfalls. The data essentially represent the snow accumulation season because the analysis was limited to days when snow depth and albedo were at least 10.2 cm and 50%. These two criteria served to limit, if not eliminate, the snowmelt period or any effect of the underlying surface. In the 18 winters a total of 232 individual runs (days between snowfalls) of albedo decay varying from 1 to 21 days in duration were found and analyzed. The major result of this study was that none of the factors considered in the aging process of snow (temperature, heat sums, sunshine, solar altitude, and time) could be used individually to successfully predict the albedo decay of single runs. A relatively strong relationship, however, was found between the mean albedos and the number of days since the last measurable snowfall; r2 = 0.84 and 0.86 for the linear and exponential equations, respectively, of all 232 runs between November and April. This was greatly superior to that found for the relationship with heat sums, which by their very nature include time as a factor. Thus, within the limits imposed upon the albedo data used, it was found that during the snow accumulation period the mean albedo decay between snowfalls can be successfully predicted only by the number of days in that interval. The mean decay rates for all months and combinations of months were generally described equally as well by linear trends as by exponential trends, in contrast to the exponential decay usually depicted. The mean linear decay rate of the December through February period was less than 1% per day in contrast to the November, March, and April linear rates that were 2.4, 2.9, and 3.3% per day, respectively. The mean albedo on the day following a snowfall greater than a trace averaged about 80% during the November?April period.