The reference evapotranspiration (ETo) is dependent on the amount of energy available in the environment, being solar radiation (SR) as an important variable in its estimation. This study was carried out in order to determine the coefficients "a" and "b" of the Angstron-Prescott equation for Seropédica, Rio de Janeiro State, Brazil, and to evaluate their effects on the SR and ETo estimation. Measures of global solar radiation and effective number of hours of sunshine were used from station Ecology Fund (83741 - INMET) for the period of 2000 to 2007. The coefficients were determined by linear regression analysis for the entire period and monthly and yearly periods. Using the calculated coefficients and those proposed by FAO (0.25 and 0.50) SR and ETo were estimated and evaluated their performance. The average monthly coefficients "a" ranged from 0.232 to 0.299 and "b" from 0.397 to 0.504. Annual mean coefficients "a" and "b" were 0.295 and 0.417, and for general period were 0.282 and 0.433, respectively. The best performance observed for the estimated SR and ETo was obtained when the monthly coefficients of the equation Angströn-Prescott were adopted.
solar radiation; sunshine; weather station; Penman-Monteith
