Badosa Jordi, Calbó Josep, Mckenzie Richard, Liley Ben, González Josep-Abel, Forgan Bruce, Long Charles N
Laboratoire de Météorologie Dynamique (LMD), Ecole Polytechnique, Palaiseau, France.
Photochem Photobiol. 2014 Jul-Aug;90(4):941-51. doi: 10.1111/php.12272. Epub 2014 Apr 17.
Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern-hemisphere mid-latitude site where a 10-years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short-time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%).
评估了云对紫外线指数（UVI）和总太阳辐射（TR）的影响，这些影响是云量和晴朗条件（来自天空图像）以及太阳天顶角（SZA）的函数。这些分析是针对南半球中纬度地区进行的，该地区有一个10年的数据集。结果证实，云对总太阳辐射的削减作用比对紫外线的削减作用更大，特别是在太阳被遮挡的条件下、低云量（<60%）和大太阳天顶角（>60°）的情况下。同样，局部短期增强效应对于总太阳辐射比对紫外线更强，主要出现在太阳可见的条件下、高云量和大太阳天顶角的情况下。开发了两种估算紫外线指数的方法：（1）根据天空成像的云量和晴朗条件进行估算，（2）根据总太阳辐射测量值进行估算。这两种方法都可用于实际应用，不过方法2总体表现最佳，因为总太阳辐射能考虑云的光学特性。方法2估算值相对于测量值的平均绝对（相对）差异为0.17个紫外线指数单位（对于1分钟数据为6.7%）和0.79个标准红斑剂量（SED）单位（对于日积分数据为3.9%）。方法1的结果准确性较低，但仍适用于估算紫外线指数：平均绝对差异为0.37个紫外线指数单位（15%）和1.6个标准红斑剂量单位（8.0%）。
