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Ice-crystal absorption: a comparison between theory and implications for remote sensing

机译：冰晶吸收：理论与遥感意义之间的比较

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The problem of the disagreement between cirrus crystal sizes determined remotely and by in situ measurements is shown to be due to inappropriate application of Mie theory. We retrieved the absorption optical depth at 8.3 and 11.1 μm from 11 tropical anvil cirrus clouds, using data from the High Resolution Infrared Radiation Sounder (HIRS). We related the absorption optical depth ratio between the two wavelengths to crystal size (the size was defined in terms of the crystal median mass dimension) by assuming Mie theory applied to ice spheres and anomalous diffraction theory (ADT) applied to hexagonal columns, hexagonal plates, bullet rosettes, and aggregates (polycrystals). The application of Mie theory to retrievals yielded crystal sizes approximately one third those obtained with ADT. The retrievals of crystal size by use of HIRS data are compared with measurements of habit and crystal size obtained from in situ measurements of tropical anvil cirrus particles. The results of the comparison show that ADT provides the more realistic retrieval. Moreover, we demonstrate that at infrared wavelengths retrieval of crystal size depends on assumed habit. The reason why Mie theory predicts smaller sizes than ADT is shown to result from particle geometry and enhanced absorption owing to the capture of photons from above the edge of the particle (tunneling). The contribution of particle geometry to absorption is three times greater than from tunneling, but this process enhances absorption by a further 35%. The complex angular momentum and T-matrix. methods are used to show that the contribution to absorption by tunneling is diminished as the asphericity of spheroidal particles is increased. At an aspect ratio of 6 the contribution to the absorption that is due to tunneling is substantially reduced for oblate particles, whereas for prolate particles the tunneling contribution is reduced by 50% relative to the sphere. # 1998 Optical Society of America OCIS codes: 010.0010, 010.2940, 280.0280, 290.4020.
机译：远程确定的和通过原位测量确定的卷云晶体尺寸之间不一致的问题被证明是由于米氏理论的不适当应用。我们使用高分辨率红外辐射探测器（HIRS）的数据，从11种热带铁砧卷云中检索了8.3和11.1μm的吸收光学深度。通过假设将Mie理论应用于冰球，将异常衍射理论（ADT）应用于六方柱，六边形板，我们将两个波长之间的吸收光学深度比与晶体尺寸（尺寸由晶体中位质量尺寸定义）相关联，子弹状花环和聚集体（多晶体）。 Mie理论在反演中的应用产生的晶体尺寸约为ADT所获得晶体尺寸的三分之一。将利用HIRS数据获取的晶体尺寸与习惯和晶体尺寸的测量结果进行比较，这些习惯和晶体尺寸是从热带铁砧卷云粒子的原位测量中获得的。比较结果表明，ADT提供了更现实的检索。此外，我们证明了在红外波长下晶体尺寸的恢复取决于假定的习惯。 Mie理论预测尺寸比ADT小的原因被证明是由于粒子的几何形状和吸收的增强，这归因于从粒子边缘上方捕获光子（隧穿）。粒子几何形状对吸收的贡献比隧道效应大三倍，但此过程将吸收进一步提高了35％。复角动量和T矩阵。方法被用来表明，随着球状颗粒非球面度的增加，隧穿对吸收的贡献减小。在纵横比为6的情况下，对于扁圆颗粒，由于隧穿而对吸收的贡献显着降低，而对于扁长颗粒，相对于球体，隧穿的贡献降低了50％。 ＃1998美国光学学会OCIS代码：010.0010、010.2940、280.0280、290.4020。

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