The Empirical Relation between Solar Radiation and Hours of Sunshine

Abstract

The variation with latitude of the regression parameters a and b in the conventional equation of Ångström type Q/QA=a+bn/N between total solar radiation on a horizontal surface (Q) and hours of bright sunshine (n) has been examined. It has been shown that the slope of the relationship b is effectively constant, while the threshold value a is a function of latitude. An empirical relationship leading to the Angström equation at each latitude & over the range 0° 60° is derived and is shown to give values in reasonable accord with previous experience. It is Q/QA2.09 cos +0.52 n/N.