Surface and atmospheric controls on the heating coefficient

Measurements of the surface radiation budgets for three surfaces—grass, soil and a cornfield—are used to evaluate the ‘heating coefficient’β, and its componentsβ _↑(=dL _↑/dR _n ) andβ _↓(=dL _↓/dR _n ). This resolution permits an analysis of the sensitivity of β to surface and atmospheric influences.β _↑ is shown, both theoretically and empirically, to be determined by surface properties. For grass and soil, the parameter functions as an index of surface desiccation.β _↓ values are large (even under clear conditions) and variable, accounting for part of the variance in β and the anomalously small and negative values reported in the literature.β _↓ values for cloudy conditions may be larger or smaller than those for clear skies. It is concluded that, unless a predictive procedure can be developed forβ _↓, the Monteith and Szeicz model is of limited use for the routine estimation of net radiation.