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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Representation of a nonspherical ice particle by a collection of independent spheres for scattering and absorption of radiation: 2. Hexagonal columns and plates - art. no. 4448
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Representation of a nonspherical ice particle by a collection of independent spheres for scattering and absorption of radiation: 2. Hexagonal columns and plates - art. no. 4448

机译：通过收集散射和吸收辐射的独立球体来表示非球形冰粒：2.六角柱和板-艺术。没有。 4448

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1] A cloud of nonspherical ice particles may be represented in radiation models by a collection of spheres, in which the model cloud contains the same total volume of ice and the same total surface area as the real cloud but not the same number of particles. The spheres then have the same volume-to-area (V/A) ratio as the nonspherical particle. In previous work this approach was shown to work well to represent randomly oriented infinitely long circular cylinders for computation of hemispherical reflectance, transmittance, and absorptance. In this paper the results have been extended to hexagonal columns and plates using a geometric optics technique for large particles and finite-difference-time-domain theory (FDTD) for small particles. The extinction efficiency and single-scattering coalbedo for these prisms are closely approximated by the values for equal-V/A spheres across the ultraviolet, visible, and infrared from 0.2 to 25 mum wavelength. Errors in the asymmetry factor can be significant where ice absorptance is weak, at visible wavelengths for example. These errors are greatest for prisms with aspect ratios close to 1. Errors in hemispheric reflectance, absorptance, and transmittance are calculated for horizontally homogeneous clouds with ice water paths from 0.4 to 200,000 g m(-2) and crystal thicknesses of 1 to 400 mum, to cover the range of crystal sizes and optical depths from polar stratospheric clouds (PSCs) through cirrus clouds to surface snow. The errors are less than 0.05 over most of these ranges at all wavelengths but can be larger at visible wavelengths because of the ideal shapes of the prisms. The method was not tested for, and is not expected to be accurate for, angle-dependent radiances. [References: 26
机译：1]在辐射模型中，非球形冰颗粒云可以由一组球表示，其中模型云包含的冰总量和真实表面积与真实云相同，但颗粒数量不相同。球体的体积/面积比（V / A）与非球形粒子相同。在以前的工作中，该方法被证明可以很好地代表随机取向的无限长圆柱体，以计算半球反射率，透射率和吸收率。本文使用几何光学技术将结果扩展到六角形柱和板，适用于大颗粒，适用于小颗粒的时域有限差分时域理论（FDTD）。这些棱镜的消光效率和单散射煤层气被波长范围为0.2至25的紫外线，可见光和红外光的等V / A球体的值近似逼近。在冰吸收率较弱的地方，例如在可见光波长下，不对称系数的误差可能很大。这些误差对于纵横比接近1的棱镜来说最大。半球形反射率，吸收率和透射率的误差是针对水平均质云计算的，其冰水路径为0.4至200,000 gm（-2），晶体厚度为1至400μm，涵盖从极地平流层云（PSC）到卷云到地表雪的晶体大小和光学深度的范围。在所有波长下，在大多数这些范围内的误差均小于0.05，但由于棱镜的理想形状，在可见光波长下的误差可能更大。该方法未经测试，并且对于与角度相关的辐射也未必准确。 [参考：26

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