Historical Albedo Values at St. Paul Minnesota, 1969–85

Abstract

Incoming and reflected hemispheric radiation were measured at St. Paul over four different surfaces (sod, alfalfa, soybeans, and green peas) for a combined total of 5778 days between 21 November 1969–31 December 1985. Statistical summaries of the calculated mean daily albedos of all surfaces are shown for mouths, seasons and years. There are, in effect, three albedo seasons: the high albedo mason with snow cover (December-February), the low albedo season (April-October), and transitions between the two that occur in March and November. The 1east variation was associated with the low albedo season, increasing from a median value of 18% in April to 24% in October. The median monthly values for the high albedo season ranged between 74%-77%. The greatest variation in albedo values occurred in March and was due to the surface varying between extremes of a fresh snow cover and a bare soil with standing water. Of the four climate seasons, only winter (December-February) was markedly different from the others. The winter median was 77% compared to a 20%–24% median albedo of the other seasons. The summer standard deviation was about one-fifth that of the other three seasons. The distribution of albedo values was such that caution must be exercised in the application of the usual statistical measures. Only summer (June-August) exhibited a distribution close to that of a normal one; the mean and median annual values 36% and 24%, respectively, emphasize the degree of nonnormality.

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