Calibration of Angstrom- Prescott Coefficients for Selected Stations of Khorasan-e Razavi Province

The solar radiation reached to the Earth surface is an important parameter in thermal balance of the Earth- Atmosphere system. In this study, the Black and Allen models were used for estimating daily global solar radiation reached to the Earth surface and the atmosphere upper layer, respectively. The estimated radiation at ground level by Black model was compared with the Pyranometer data at Mashhad station. The results showed that there was little difference between the amount of radiation measured with Pyranometer and the estimated one by the Black model. Then the coefficients of Angstrom-Prescott model for Mashhad station, was calibrated. In the next stage, the obtained results were compared with the Angstrom-Prescott models that had been proposed in previous researches for Mashhad station. The results showed that the developed model in this study had a high accuracy. Root mean squared error values for the model proposed here by authors, Alizadeh and Khalili and FAO were obtained 4.57, 4.61 and 5.02 MJ M-2 day-1, respectively. Then, the Angstrom-Prescott coefficients at other stations of Khorasan Razavi Province were calibrated using values obtained by the Black and Allen relations. Finally, the obtained radiation values on a horizontal surface on ground level using ordinary Kriging were mapped. The results of the mapping of radiation showed that the southern areas of the province had more potential from the view of receiving solar radiation.