A Three-Year Study of Net Radiation at St. Paul, Minnesota

Abstract

This study is based upon net radiation measurements made with a Suomi-type ventilated net radiometer. The average annual net radiation was 36,247 ly for the study period 1 April 1964–31 March 1967. April–October showed positive net radiation totals, November–February negative net radiation totals, and March had positive net radiation totals in two of the three years studied. Only fourteen days with all negative net radiation and two days with all positive net radiation occurred in the three-year period. Average daily time of positive net radiation ranged from 244 min in January to 749 min in June. Although positive net radiation exceeded negative net radiation an average of 36,247 ly per year, negative or null net radiation was recorded 63% of the time. The ratio of net radiation to incoming solar radiation varied widely during the year. However, from May–August the ratio ranged only from 0.45–0.54 for any one month during the three years and averaged 0.50. Monthly net radiation values calculated by the method described by Sellers were within 10% or less of the measured values for all but two months. Budyko's calculated annual value of ∼35,000 ly also agreed favorably with the average measured value.