Calibrating the ?ngstr?m-Prescott Model with Solar Radiation Data Collected over Long and Short Periods of Time over the Tibetan Plateau

As the coefficients of the angstrom ngstrom-Prescott model is site-dependent, the sparsity of radiation stations in regions like the Tibetan Plateau (TP) presents challenges for model calibration. Due to the unique climate and the clean air conditions over the TP, it might be feasible to calibrate the angstrom ngstrom-Prescott model with short-term observations from scientific expeditions. To test this hypothesis, we used various datasets with different lengths at four stations, together with 435 daily radiations measured during a scientific expedition at Banga in the central TP from 2014 to 2015, to calibrate the angstrom ngstrom-Prescott model. We found that calibration with a 1-year data length resulted in model performances comparable to those with a 20-year data length. Analysis of the expedition observations showed that the monthly average daily radiation ranged from 15.2 MJ/m(2)d in December 2014 to 26.5 MJ/m(2)d in July 2015, with an average value of 20.6 MJ/m(2)d. When this set of expedition data was used for calibration, the angstrom ngstrom-Prescott model performed well with an NSE (Nash-Sutcliffe efficiency) of 0.820. If no data were available for calibration, the coefficients of the angstrom ngstrom-Prescott model could also be directly calculated by parameterization methods established with calibrations at the other radiation stations. In this situation, the LiuJD method performed the best with the highest NSE of 0.792, followed by the LiuXY method with an NSE of 0.764. The FAO method performed poorly with an NSE of 0.578, while the Gopinathan method performed the worst with the lowest NSE of 0.218. Thus, the best strategy to calibrate the angstrom ngstrom-Prescott model in the Tibetan Plateau is to use data from local observations, even if collected over short periods. When these are not available, the coefficients of the angstrom ngstrom-Prescott model should be calculated using the parameterization method established with calibrations over the Tibetan Plateau.