The characteristics of net radiation (R n) (0.3-10 μm) in Lhasa and Haibei in the Tibetan Plateau were analyzed based on long-term in-situ measurements of surface radiation data.The monthly average of daily R n reached a minimum during the winter period followed by an increase until May and then a decline until January.This variation is consistent with solar activity.The annual mean daily total R n values were 0.92 MJ m 2 d 1 and 0.66 MJ m 2 d 1 in Lhasa and Haibei,respectively.A relationship between R n and broadband solar radiation (R s) was demonstrated by a good linear correlation at the two sites.R n can be an accurate estimate from R s.The estimated R n values were similar to the observed values,and the relative deviations between the estimates and measurements of R n were 2.8% and 3.8% in Lhasa and Haibei,respectively.The application of the R n estimating model to other locations showed that it could provide acceptable estimated R n values from the R s data.Furthermore,we analyzed the influence of clouds on R n by different clear index (K s),defined as the ratio of R s to the extraterrestrial solar irradiance on a horizontal surface.The results indicate that more accurate results are associated with increased cloudy conditions.The influence of the albedo was also considered,but its inclusion in the model resulted in only a slight improvement.Because surface albedo is not usually measured,an expression based solely on global solar radiation could be of more extensive use.
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