Estimating incident terrestrial radiation under all atmospheric conditions

Abstract

To apply a complete energy balance to the computation of evaporation or snowmelt, radiation data are necessary. At present there is a reasonably adequate network of incident solar radiation stations. However, a network of all‐wave radiometers does not exist. It is therefore evident that to apply the energy budget technique to hydrological problems, incident long‐wave radiation has to be estimated. An empirical equation is developed by which incident long‐wave radiation can be computed from observations of surface air temperature, vapor pressure, and incident solar radiation. Based on comparisons of estimated and observed incident long‐wave radiation at six locations, the following conclusions seem warranted: (1) The equation should give results comparable within a few percent on a long‐term basis (six months or longer); (2) For any specific atmospheric condition, there seems to be no tendency for the equation to over or under compute or to give increased scatter; (3) When data for periods of six‐months or more were analyzed, correlation coefficients of approximately 0.90 were obtained between computed and observed daily radiation values.