Sky Cover Influence on Total Hemispheric Radiation During Daylight Hours

Abstract

Effects of sky cover variations on daylight total hemispheric radiation were determined from measurements made at Columbia, Mo. Total hemispheric radiation was measured by a Beckman and Whitley radiometer, solar radiation by an Eppley pyrheliometer, and sky cover by photoelectric scanning of whole-sky negatives. Regressions were calculated relating values of incoming radiation during daylight hours to sky cover. Daily total hemispheric radiation was expressed using values of sky cover and the amount of radiation received at the top of the atmosphere. Average hourly hemispheric and downward solar radiation received during daylight hours was expressed as functions of the second power of sky cover, except for large solar zenith angles. Decreases in total hemispheric radiation with increasing sky cover were attributed mainly to decreases in values of the incoming solar radiation component.