拉萨紫外辐射特征分析及估算公式的建立

本文利用2005~2010年的辐射观测资料对拉萨地区紫外辐射的时间变化特征及紫外辐射与总辐射比值的变化特征进行了分析,结果表明,紫外辐射与太阳总辐射的变化规律基本一致,日变化表现为正午大、早晚小；季变化特征是夏季6月最大,冬季1月最小.紫外辐射日累积值6年平均为0.87 MJ·m-2·d-1；紫外辐射有逐年递减的趋势.紫外辐射与总辐射比值也存在着明显日变化,表现为正午大、早晚小的规律；其季节变化也是夏季最大,冬季最小.紫外辐射与总辐射比值6年平均为0.0418；紫外辐射与总辐射比值也呈现逐年递减的趋势.利用2010年大气质量数和晴空指数,建立了适合于拉萨紫外辐射估量的公式,估算值的瞬时值与观测值的平均相对误差最大为8.66%,紫外辐射日累积重构值与观测值平均相对误差仅为5.5%.

The Analysis of Variation Characteristics and Establishing of Estimating Equation for Ultraviolet Radiation in Lhasa

The temporal variation of ultraviolet (UV) radiation and the ratio of UV radiation to broadband solar radiation were analyzed in Lhasa using the radiation observations during 2005-2010, the results indicate that the UV radiation has consistent variation characteristics with the solar radiation. The highest value of daily UV radiation was measured at noon while the lowest value occurred in the morning or night, the highest value of monthly UV radiation was measured in June while the lowest value occurred in January. The annual mean daily UV radiation was 0.87 MJ·m^-2·d^-1 during this period, with a decreased trend. The ratio of UV radiation to solar radiation has obvious diurnal variation characteristics, namely, the highest value appeared at noon while the lowest value occurred in the morning or night, the seasonal highest value occurred in summer while the lowest value occurred in winter. The mean ratio of UV radiation to solar radiation was 0.0418, which also has a decreased trend in the six years. Finally, an experimental estimating equation was established by using the optical air mass and the clearness index in 2010. This model can estimat UV radiation with high accuracy at the site where the model was developed. The mean bias error was close to zero, and the relative errors were less than 8.66% and 5.5% for instantaneous and daily UV radiation, respectively.