estimating the solar radiation in mashhad:the optimal empirical method vs. seven temporal scales

the solar radiation received by earth surface is one of the most applicable parameter that is so important in hydrology, agriculture, meteorology and climatological modeling. because of very expensive instrument for measuring the radiation, researchers suggested many different experimental equations to estimate this parameter in different climate. seven models which are calibrated for semi-arid climate of mashhad were used to find the optimum model for this area. these models are angstrom–prescott suggested by fao, calibrated model of angstrom–prescott by khalili and rezaei sadr (1 and 2), calibrated model of angstrom–prescott by alizadeh and khalili, linear regression model of alizadeh and khalili, sabbagh model and glover and mcculoch. results show that in daily scale the calibrated model of angstrom–prescott by khalili and rezaei sadr including atmospheric water vapor spectrum is the best model in mashhad’s climate where ، ، and . also in this scale, the calibrated model of angstrom–prescott by khalili and rezaei sadr and linear regression model of alizadeh and khalili are in the second and third order respectively. it is also found that in the monthly scale, the glover and mcculoch model is the best one where ، ، and .