Aircraft measurements of the solar and infrared radiative properties of cirrus and their dependence on ice crystal shape
Aircraft measurements of the solar and infrared radiative properties of cirrus and their dependence on ice crystal shape
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飞机测量卷云的太阳和红外辐射特性及其对冰晶形状的依赖性
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
A. Baran
中科院分区：
文献类型：
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作者：
P. Francis;J. Foot;A. Baran
我们提出了飞机测量薄卷云的辐射传输特性的苏格兰东海岸1995年11月9日采样。从卷云下方测量了0.87、1.61、3.7、8.55和11.0 μm的下行辐射，从而覆盖了大范围的尺寸参数和冰折射率，并能够推导出卷云光学厚度、有效晶体尺寸和散射相函数的信息。这些量的敏感性，在计算中假设的冰晶形状进行检查，并与原位数据的结果进行比较。我们发现，一个随机的多晶形状产生的有效尺寸是一致的，在所有考虑的波长的原位数据，并在这方面比其他晶体形状的分析表现更好。然而，从0.87 μm辐射中获得的光学厚度远小于从11.0 μm数据中获得的光学厚度，这意味着在太阳波长处的相位函数在整个散射角范围的很大一部分上都是错误的。从实验室测量得出的经验相位函数产生的光学厚度与11.0 μm和原位数据更一致，并且比使用任何模型晶体形状计算的散射辐射的角分布更准确地匹配。反常衍射近似与8.55 μm和11.0 μm处的测量结果符合得很好。
We present aircraft measurements of the radiative transfer properties of thin cirrus cloud sampled off the east coast of Scotland on November 9, 1995. Downwelling radiances were measured from below the cirrus at 0.87, 1.61, 3.7, 8.55, and 11.0 μm, thereby covering a large range of size parameter and ice refractive index and enabling information on cirrus optical thickness, effective crystal size, and scattering phase function to be deduced. The sensitivity of these quantities to the ice crystal shape assumed in the calculations is examined, and the results are compared with in situ data. We find that a randomized polycrystal shape produces effective sizes that are consistent with the in situ data across all wavelengths considered and performs better in this respect than the other crystal shapes analyzed. However, the optical thicknesses retrieved from the 0.87 μm radiances for this shape are considerably less than those derived from the 11.0 μm data, implying that the phase function at solar wavelengths is in error for this shape over a significant portion of the full scattering angle range. An empirical phase function derived from laboratory measurements produces optical thicknesses which are more consistent with the 11.0 μm and in situ data and matches the angular distribution of scattered radiance more accurately than that calculated using any of the model crystal shapes. The anomalous diffraction approximation is found to produce good agreement with the measurements at 8.55 and 11.0 μm for the crystal sizes relevant to the present case study.