The regression of net radiation upon solar radiation
Tóm tắt
A number of studies have sought to relate net radiation over natural surfaces to incoming global radiation. Several deficiencies are noted in interpretation of the simple regression models used for this purpose in the past. A modification proposed for correction of these deficiencies introduces a new longwave exchange coefficient, λ, that relates the change in net longwave radiation to the change in net shortwave radiation. This coefficient is a conceptual improvement of β, the surface heating coefficient that has gained some acceptance. The definition of a unique λ for various surfaces is shown to be the same problem faced by past studies that have sought to develop a unique regression equation over each surface. The coefficient λ may serve as an index of the surface properties that govern the dissipation of absorbed global radiation. We recognize that this index is also affected by environmental characteristics. Interpretation of the index is demonstrated for three types of surfaces under cloudless skies: a desert, a forest, and an irrigated crop. Further consideration of the coefficient λ reveals that the apparent success of regression relations linking net and global radiation may often be attributed to negligible variation of longwave exchange rather than to the soundness of a particular regression model.
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Tài liệu tham khảo
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