Day‐time long‐wave radiation from the sky

Six months of records of the hemispheric flux F of long‐wave radiation at Aspendale, Victoria, are analysed. A day‐time correction to Swinbank's formula for the radiation from clear skies is established, and this correction is probably applicable also to other more accurate formulae which include a term dependent on screen level humidity. It varies with time of day and season, but is of the order of − 3 mW cm −2 on summer afternoons. The correction is applied to all‐weather data, and at Aspendale the average long‐wave radiation at the ground due to clouds is found to be 0.6 mW cm −2 /tenth of cloud cover. The mean value of F under cloudy skies is sensibly constant throughout the day, and is not greatly influenced by the diurnal variation of screen temperature.