Impact of Cirrus Crystal Shape on Solar Spectral Irradiance: A Case Study for Subtropical Cirrus
Impact of Cirrus Crystal Shape on Solar Spectral Irradiance: A Case Study for Subtropical Cirrus
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DOI：
10.1029/2004jd005294
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发表时间：
2005-02
影响因子：
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通讯作者：
M. Wendisch;P. Pilewskie;J. Pommier;S. Howard;P. Yang;A. Heymsfield;C. Schmitt;D. Baumgardner;B. Mayer
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文献类型：
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作者：
M. Wendisch;P. Pilewskie;J. Pommier;S. Howard;P. Yang;A. Heymsfield;C. Schmitt;D. Baumgardner;B. Mayer
[1]利用实测的副热带卷云冰晶粒度分布廓线计算了云上、云下的太阳光谱辐照度。在计算中假设了球形和非球形冰晶习性（柱状、中空、片状、子弹状和聚集体）。模拟结果进行了比较，从美国航天局太阳光谱通量辐射计的辐照度测量。在CRYSTAL-FACE期间，三架飞机收集了微物理和辐射数据。对2002年7月26日和23日两次使命中的两个卷云（光学厚度分别为1和7）进行了详细的研究。对于大多数冰晶习性，卷云上方的下降流和上升流辐射谱的测量值大多可以由辐射模型再现到±5-10%以内。在卷云下面，由于表面的微物理变化沿着飞行轨迹，以及微物理和辐照度测量之间的非最佳搭配，模拟结果与测量的辐照度不一致。晶体的形状特征的影响是重要的光学薄卷云上方的反射辐照度，特别是对于小的太阳天顶角，因为在这种情况下，单散射占主导地位的太阳辐射场。对于中等光学厚度的卷云，增强的多重散射倾向于减少由非球形单次散射引起的特定形状特征。在冰的吸收带内的形状相关的个别非球形冰晶的吸收特性的差异被放大，如果多重散射盛行。此外，它被发现，在云的形状敏感性的下降流的辐射光谱是较大的相比，非球形的影响，上面的卷云反射的辐射。最后，它表明，计算的卷云太阳辐射强迫可以变化高达26%，这取决于冰晶的习惯。
[1] Profiles of in situ measurements of ice crystal size distribution of subtropical cirrus were used to calculate solar spectral irradiances above and below the clouds. Spheres and nonspherical ice crystal habits (columns, hollows, plates, bullets, and aggregates) were assumed in the calculations. The simulation results were compared to irradiance measurements from the NASA Solar Spectral Flux Radiometer. The microphysical and radiation data were collected by three aircraft during CRYSTAL-FACE. Two cirrus cases (optical thickness of about 1 and 7) from two mission dates (26 and 23 July 2002) were investigated in detail. The measured downwelling and upwelling irradiance spectra above the cirrus could mostly be reproduced by the radiation model to within ±5–10% for most ice crystal habits. Below the cirrus the simulations disagreed with the measured irradiances due to surface albedo variability along the flight track, and nonoptimal colocation between the microphysical and irradiance measurements. The impact of shape characteristics of the crystals was important for the reflected irradiances above the optically thin cirrus, especially for small solar zenith angles, because in this case single-scattering dominated the solar radiation field. For the cirrus of moderate optical thickness the enhanced multiple scattering tended to diminish particular shape features caused by nonspherical single-scattering. Within the ice absorption bands the shape-related differences in the absorption characteristics of the individual nonspherical ice crystals were amplified if multiple scattering prevailed. Furthermore, it was found that below the cloud the shape sensitivity of the downwelling irradiance spectra is larger compared to the nonsphericity effects on reflected irradiances above the cirrus. Finally, it was shown that the calculated cirrus solar radiative forcing could vary by as much as 26% depending on the ice crystal habit.