An empirical method for estimating long‐wave radiation exchanges in the British Isles

Abstract From radiation measurements at Kew Observatory (tabulated by Lönnqvist), the effective emissivity of the atmosphere ε, defined as the ratio of incoming long‐wave radiation to black‐body radiation at screen temperature, can be related to optical path m (cm) by With standard deviation ± 0·018. The relation between m and surface vapour pressure e (mb) found from Belasco's (1952) air mass analysis is giving almost the same as Brunt's equation from Benson data. Net long‐wave radiation L over short grass can be calculated from where c is fractional cloudiness; σ T A is black‐body radiation at screen temperature; Δ L 1 is a correction for the difference between T A and cloud‐base temperature; and Δ L 2 for the difference between T A and surface radiative temperature. From Roach's Kew data, Δ L 1 = – 18 cal cm −2 day −1 and Δ L 2 varies with season from – 12 cal cm −2 day −1 (December) to + 20 cal cm −2 day −1 (June). Throughout the British Isles, annual mean L with c = 0 is close to – 200 cal cm −2 day −1 , and for real values of c Estimated annual net (total) radiation is 29 k cal cm −2 with little variation over the British Isles.