Estimativas da radiação solar direta normal através de um modelo parametrizado, na ausência de nuvens

Abstract

The hourly and daily of direct radiation under cloudless skies are estimated for Januaria, State of Minas Gerais, Brazil, using the parameterization Model C presented by Iqbal (1983). This model takes into account absorption of radiation by molecules such a O3, H2O and the uniformly mixed gases. Attenuation by Rayleigh scattering and aerosol extinction are included. Aerosol attenuation is calculated through of the visibility atmospheric. The input parameters include the ozone content, visibility, hourly temperature, pressure and relative humidity data. Measured values of the direct solar radiation from May through July 1992 were used to validate the model. The hourly and daily values for the Model compared very well with measured values for clear days, showing an accuracy better than 1 per cent for daily values and 4 per cent for hourly values in the main radiation period (9-16 hours). The parameterization of the transmitance of the various atmospheric constituents are also analyzed. Results are presented to show the effect of variation of water vapor content and visibility.