Variation Characteristics of Ultraviolet Radiation in the Sanjiang Plain

The variation characteristics of ultraviolet radiation (UV) in the Sanjiang region of Northeast China were analyzed using radiation data from 2005 to 2011. The temporal variation of the ratio of UV to broadband solar radiation (SR) was also analyzed. The results indicated that the temporal variation characteristics of UV and SR were similar. At the diurnal scale, the highest daily UV value was measured at noon, whereas the lowest was recorded in the morning or night. The highest monthly UV value was recorded in the summer, whereas the lowest in winter. In the Sanjiang region, the annual average daily UV was 0.53 MJ m^-2 d^-1. The variation characteristics of the UV and the ratio of UV to SR were the same. Daily, the highest value of the ratio of UV to SR was recorded at noon, whereas the lowest value was recorded in the morning or night. Yearly, the highest value was recorded in the summer, whereas the lowest in winter. The mean value of the UV to SR ratio was 0.0433 in this observation period of 2005-2011. Furthermore, an empirical equation for estimating the UV was established by using the in situ observations for 2011. The equation parameters include the relative optical air mass and clearness index. The equation can be widely used to obtain the UV from SR measurements. The largest relative error between observed and model UV data was 8.5% and 6.1% for instantaneous and daily values, respectively.