MATHEMATICALLY INTEGRABLE PARAMETERIZATION OF CLEAR-SKY BEAM AND GLOBAL IRRADIANCES AND ITS USE IN DAILY IRRADIATION APPLICATIONS

A simple parameterized clear-sky short-wave irradiance model is derive d from a detailed two-band physical model presented earlier, The input s for the parameterized model (called PSIM) are the solar elevation, t he amount of precipitable water(w), the Angstrom turbidity coefficient (beta), the station's pressure (or its altitude), and the zonal surfa ce albedo (for which a simple submodel is provided for North America). PSIM is intended to give accurate irradiance estimates in any atmosph eric condition whenever w < 5 cm and beta < 0.45. The parameterization uses a function of solar elevation that is integrable with time, so t hat a parameterized daily irradiation model (called DIM) is also obtai ned. The seasonal variations of the daily clear-sky beam and global ir radiations are presented for different combinations of w, beta, and la titude. It is possible to use these irradiation estimates in different applications when dealing with solar energy or climatology. For examp le, a simple way to derive the mean monthly apparent solar elevation o r air mass is given. It is also suggested that the original Angstrom's equation (to derive the average global irradiation from the fraction of possible sunshine) be used more extensively with DIM. Finally, it i s demonstrated (using data from Albany, NY) that the monthly average b eam irradiation may be obtained with a very simple equation from the f raction of possible sunshine and DIM, yielding more accurate estimates than the existing best-performing method.