Variation characteristics of ultraviolet radiation over the north china plain

In situ measured data of broadband solar radiation (R (s)) and ultraviolet (U (v)) radiation were used to investigate the spatiotemporal variation properties of U (v) radiation and the ratio of U (v) radiation to R (s) over the North China Plain (NCP). Based on the analysis, an empirical model for estimating U (v) radiation under all weather conditions in this region was developed. The results showed that the annual U (v) radiation over the NCP ranges from 0.38-0.52 MJ m(-2) d(-1). The highest value during the study period was recorded at the Changwu site, which is located near the margin of the Loess Plateau, while the lowest value appeared at the station in Beijing. The seasonal variation pattern of the ratio of U (v) radiation to R (s) is similar to that of U (v) radiation; namely, the highest value appears in August and then decreases gradually until the lowest value appears in November. A small increasing trend in the U (v) radiation levels and the ratio of U (v) radiation to R (s) was observed over the NCP. The evaluation results showed that the empirical estimation model can be widely used to estimate U (v) radiation under all atmospheric conditions. The relative error between the modeled and measured daily values were within +/- 15%.