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首页> 外文期刊>Journal of Applied Meteorology >The Angular Distribution of UV-B Sky Radiance under Cloudy Conditions: A Comparison of Measurements and Radiative Transfer Calculations Using a Fractal Cloud Model
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The Angular Distribution of UV-B Sky Radiance under Cloudy Conditions: A Comparison of Measurements and Radiative Transfer Calculations Using a Fractal Cloud Model

机译：多云条件下UV-B天空辐射的角分布：使用分形云模型进行的测量和辐射传递计算的比较

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摘要

In recent years, global warming concerns have focused attention on cloud radiative forcing and its accurate encapsulation in radiative transfer measurement and modeling programs. At present, this process is constrained by the dynamic movement and inhomogeneity of cloud structure. This study attempts to quantify the UV sky radiance distribution induced by a partial and overcast stratiform cloud field while addressing some of the inherent spatial and temporal errors resulting from cloud. For this purpose, high-quality azimuthally averaged 2-min measurements of erythemal UV-B sky radiance distribution were undertaken by a variable sky-view platform at Hobart, Australia (42.90°S, 147.33°E). Measurements were subsequently compared with Monte Carlo radiative transfer simulations using both a multifractal and plane-parallel homogenous (PPH) cloud field Data were also compared with several empirical parameterizations. Results at solar zenith angles of 30°and 50°show that for overcast conditions, the multifractal model is superior to the PPH model. For broken cloud conditions, the radiance measurements are biased toward higher instances of direct-beam interruption by cloud. This tends to smooth the near-sun sky radiance field whereas the multifractal model under the same conditions continues to exhibit the circumsolar effect, indicating that its performance may be still valid for radiation modeling. An empirical parameterization of the same multifractal model produced similar sky radiance profiles, warranting its use in radiative transfer models.
机译：近年来，全球变暖问题将注意力集中在云辐射强迫及其在辐射传递测量和建模程序中的精确封装上。目前，这一过程受到云结构的动态运动和不均匀性的限制。这项研究试图量化由部分和多云的层状云场引起的紫外线天空辐射分布，同时解决由云引起的一些固有的时空误差。为此，在澳大利亚霍巴特（42.90°S，147.33°E）的可变天空视野平台上对红斑UV-B天空辐射度分布进行了高质量的方位角平均2分钟测量。随后将测量结果与使用多重分形和平面平行均质（PPH）云场的Monte Carlo辐射传输模拟进行了比较。还将数据与几种经验参数化进行了比较。太阳天顶角为30°和50°时的结果表明，在阴天条件下，多重分形模型优于PPH模型。对于破云条件，辐射测量偏向于被云直接光束中断的较高实例。这趋于使近日天空辐射场平滑，而在相同条件下的多重分形模型继续表现出绕太阳效应，表明其性能可能仍对辐射建模有效。相同的多重分形模型的经验参数化产生了相似的天空辐射度剖面，从而保证了其在辐射传递模型中的使用。

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