A test of the ability of current bulk optical models to represent the radiative properties of cirrus cloud across the mid- and far-infrared
A test of the ability of current bulk optical models to represent the radiative properties of cirrus cloud across the mid- and far-infrared
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DOI：
10.5194/acp-20-12889-2020
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发表时间：
2020-11-05
影响因子：
6.3
通讯作者：
Pickering, Juliet C.
中科院分区：
文献类型：
--
作者：
Bantges, Richard J.;Brindley, Helen E.;Pickering, Juliet C.
在卷云耦合云 - 辐射实验（CIRCCREX）期间，从英国机载大气测量设施（FAAM）的BAe 146飞机获得的中红外到远红外天底辐射率测量值，被用于评估各种冰云体光学特性模型的性能。通过使用最小化方法，我们发现模拟能够在测量不确定度范围内重现中红外波段的观测光谱，但无法同时匹配远红外频率范围内的观测结果。当同时使用中红外和远红外观测来最小化残差时，性能最佳的模拟与观测之间光谱通量差异的一阶估计表明，中红外和远红外之间存在补偿效应，使得绝对宽带差异<0.7 W m⁻²。然而，单独使用中红外（远红外）观测来匹配光谱会导致大得多的差异，绝对差异达到约1.8（3.1）Wm⁻²。这些结果表明，使用这些微物理模型的模拟可能会给出大致正确的长波辐射综合影响，但这掩盖了光谱误差，对大气加热的垂直分布有隐含影响。它们还意味着，单独应用这些模型对中红外辐射率进行反演时，所选取的卷云光学特性将与远红外辐射率不一致。因此，这些结果凸显了更广泛的远红外观测对于评估以及在必要时改进当前冰体光学模型的潜在益处。
Measurements of mid- to far-infrared nadir radiances obtained from the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 aircraft during the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX) are used to assess the performance of various ice cloud bulk optical property models. Through use of a minimization approach, we find that the simulations can reproduce the observed spectra in the mid-infrared to within measurement uncertainty, but they are unable to simultaneously match the observations over the far-infrared frequency range. When both mid- and far-infrared observations are used to minimize residuals, first-order estimates of the spectral flux differences between the best-performing simulations and observations indicate a compensation effect between the midand far-infrared such that the absolute broadband difference is < 0.7 W m(-2). However, simply matching the spectra using the mid-infrared (far-infrared) observations in isolation leads to substantially larger discrepancies, with absolute differences reaching similar to 1.8 (3.1) Wm(-2). These results show that simulations using these microphysical models may give a broadly correct integrated longwave radiative impact but that this masks spectral errors, with implicit consequences for the vertical distribution of atmospheric heating. They also imply that retrievals using these models applied to mid-infrared radiances in isolation will select cirrus optical properties that are inconsistent with far-infrared radiances. As such, the results highlight the potential benefit of more extensive farinfrared observations for the assessment and, where necessary, the improvement of current ice bulk optical models.