Surrogate cloud fields generated with the iterative amplitude adapted Fourier transform algorithm
Surrogate cloud fields generated with the iterative amplitude adapted Fourier transform algorithm
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使用迭代幅度自适应傅里叶变换算法生成的替代云场
DOI：
10.1111/j.1600-0870.2006.00160.x
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
A. Macke
中科院分区：
文献类型：
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作者：
V. Venema;S. Meyer;S. G. García;Anke Kniffka;C. Simmer;S. Crewell;U. Löhnert;T. Trautmann;A. Macke
本文提出了一种新的生成二维和三维云场的方法，它与真实的实测云场具有一些重要的统计特性，著名的算法如Fourier方法和Bounded Cascade方法生成具有特定Fourier谱的云场。新的迭代方法可以同时确定感兴趣的参数（例如液态水含量或液态水路径）的功率谱和幅度分布，因此，该方法非常适合于基于测量数据生成云场，并且能够生成破碎云场。这种云场的重要应用是例如闭合研究。该算法可以提供额外的空间约束，这可以减少这种研究所需的测量案例的数量。在这项研究中，通过比较积云和层积云分辨模式的云场与它们的代理场在最低点的辐射特性，以及太阳天顶角为0 °和60 °，来评价该算法对辐射问题的适用性。积云替代云最终与它们所基于的大涡模拟（LES）云相同，除了平移和反射。层积云透过率场和反射率场的均方根差小于辐射收支的0.03%。辐射率和平均光化通量拟合好于2%。这些结果表明，这些LES云很好地描述了从辐射的角度来看，只使用功率谱连同振幅分布。
A new method of generating two-dimensional and three-dimensional cloud fields is presented, which share several important statistical properties with real measured cloud fields.Well-known algorithms such as the Fourier method and the Bounded Cascade method generate fields with a specified Fourier spectrum. The new iterative method allows for the specification of both the power spectrum and the amplitude distribution of the parameter of interest, e.g. the liquid water content or liquid water path. As such, the method is well suited to generate cloud fields based on measured data, and it is able to generate broken cloud fields. Important applications of such cloud fields are e.g. closure studies. The algorithm can be supplied with additional spatial constraints which can reduce the number of measured cases needed for such studies. In this study the suitability of the algorithm for radiative questions is evaluated by comparing the radiative properties of cloud fields from cloud resolving models of cumulus and stratocumulus with their surrogate fields at nadir, and for a solar zenith angle of 0◦ and 60◦. The cumulus surrogate clouds ended up to be identical to the large eddy simulation (LES) clouds on which they are based, except for translations and reflections. The root mean square differences of the stratocumulus transmittance and reflectance fields are less than 0.03% of the radiative budget. The radiances and mean actinic fluxes fit better than 2%. These results demonstrate that these LES clouds are well described from a radiative point of view, using only a power spectrum together with an amplitude distribution.