Reconstruction of daily ultraviolet radiation for nine observation stations in China

The aim of this study was to reconstruct daily ultraviolet (UV) radiation (daily cumulation, similarly hereinafter) for nine observation stations in China, using a radiative transfer model combined with empirical relationships. Measurements of global total solar (G) radiation, UV radiation, and their ratio (UV/G) at the nine stations were analyzed for the period 2006–2011. The daily cloud and aerosol attenuation ratios were defined to quantitatively evaluate the effect of cloud and aerosols on radiation, based on measurements and simulated data under cloudless-sky conditions. A semi-empirical reconstruction method for UV radiation was established at each station using cloud modification factors, and by applying an equation that relates G and UV radiation measurements, as well as their corresponding simulations under cloudless conditions. Daily UV radiation values were reconstructed and compared with ground-based measurements for the nine stations, and the results revealed most of the slope values to be close to one, and the determination coefficients ranged from 89.5 to 95.7 %. The values of mean absolute bias error (MABE) and root-mean-square error (RMSE) were below 15 and 18 % for all stations, respectively, and at most stations were even lower than 10 %. A comparison of monthly measured and reconstructed UV radiation for the nine stations was also performed, revealing the values of MABE and RMSE to be even smaller with values of less than 5 %. According to these results, we conclude that the method established in this study has good applicability and transferability.