Angströn-Prescott Coefficients for Estimating Solar Radiation in Rio Grande do Sul

Abstract The objective of this study was determine the coefficients b0 and b1 of the Angströn-Prescott equation for several locations in the State of Rio Grande do Sul using solar radiation data measured with electronic pyranometers and sunshine duration data measured with a analytical sunshine recorder and map theses coefficients for the entire state. Solar radiation data, measured by electronic pyranometer, and sunshine data, measured with a conventional Campbell-Stokes sunshine recorder in the Automatic and Conventional Weather Stations of the National Institute of Meteorology, respectively, for 13 locations across the state, were used. The values of the coefficients b0 and b1 were determined through linear regression analysis between solar radiation ratio and sunshine ratio for data grouped monthly and annually. Maps with the spatial variability of the coefficients across the State were built using the Cressman objective interpolation analysis. The coefficients b0 and b1 of the Angströn-Prescott equation were updated for the 13 locations across the State and for other locations they can be estimated from maps. The coefficient b0 decreases during winter and increases during summer whereas the coefficient b1 is greater during winter and spring months.