Understanding effective diameter and its application to terrestrial radiation in ice clouds
Understanding effective diameter and its application to terrestrial radiation in ice clouds
复制标题
了解有效直径及其在冰云地面辐射中的应用
DOI：
--
复制
发表时间：
2010
期刊：
影响因子：
--
通讯作者：
B. Baker
中科院分区：
文献类型：
--
作者：
D. Mitchell;R. Lawson;B. Baker
摘要。云的“有效直径”或“有效半径”本质上是云的粒径分布（PSD）体积除以其投影面积，被广泛应用于大气辐射传输、气候模拟和遥感等领域。这源于这样一个假设，即PSD的光学性质可以用它们的有效直径、D e和云水含量（CWC）来唯一地描述，因此称为D e -CWC假设。这项研究挑战了这一假设，表明虽然D e -CWC假设对液态云似乎普遍有效，但在以下区域，它似乎不太有效：(1)吸收主要不是PSD冰水含量（IWC）或PSD投影面积的函数，以及(2)波共振（即光子隧穿）对吸收有显著贡献的区域。当D e D e -CWC假设最不可靠时，这两个区域往往在陆地波长上强烈重合。仅用D e和IWC来处理光学性质可能会导致窗口区域陆地辐射的吸收和消光系数以及单次散射反照率分别误差高达24%，26%和20%。窗区外的吸收和消光误差可达33%和42%。这些误差的大小和符号可随波长迅速变化，这可能在气候模拟、遥感和其他与辐射波长依赖性有关的应用中产生重大误差。当D e -CWC假设失效时，冰云光学性质似乎取决于D e、IWC和PSD形状。基于历史PSD测量的气候模型和遥感算法中的光学特性参数化可能由于先前未知的PSD误差而出现误差（例如，由于采样期间较大的冰颗粒在探针入口管上破碎而存在冰伪影）。最近开发的云探测器旨在减轻这种破碎问题。在给定的温度（和/或IWC）和云类型下使用真实的PSD形状可以最大限度地减少冰光学参数化和遥感算法中与PSD形状相关的误差。虽然使用两种冰光学方案（Yang等人，2005年的数据库和修正的反常衍射近似，或MADA）来研究这个主题，但使用MADA可以对D e -IWC假设的局限性进行物理理解。相对于其他光学过程，MADA允许人们近似光子隧穿对吸收的贡献，这揭示了关于D e -IWC假设的部分误差可能与隧穿有关。通过将剩余误差与大块冰中由于吸收而产生的辐射穿透深度（Δ L）联系起来，用D e和Δ L描述了D e -IWC假设最弱的区域。
Abstract. The cloud property known as "effective diameter" or "effective radius", which in essence is the cloud particle size distribution (PSD) volume at bulk density divided by its projected area, is used extensively in atmospheric radiation transfer, climate modeling and remote sensing. This derives from the assumption that PSD optical properties can be uniquely described in terms of their effective diameter, D e , and their cloud water content (CWC), henceforth referred to as the D e -CWC assumption. This study challenges this assumption, showing that while the D e -CWC assumption appears generally valid for liquid water clouds, it appears less valid for ice clouds in regions where (1) absorption is not primarily a function of either the PSD ice water content (IWC) or the PSD projected area, and (2) where wave resonance (i.e. photon tunneling) contributes significantly to absorption. These two regions often strongly coincide at terrestrial wavelengths when D e D e -CWC assumption appears poorest. Treating optical properties solely in terms of D e and IWC may lead to errors up to 24%, 26% and 20% for terrestrial radiation in the window region regarding the absorption and extinction coefficients and the single scattering albedo, respectively. Outside the window region, errors may reach 33% and 42% regarding absorption and extinction. The magnitude and sign of these errors can change rapidly with wavelength, which may produce significant errors in climate modeling, remote sensing and other applications concerned with the wavelength dependence of radiation. Where the D e -CWC assumption breaks down, ice cloud optical properties appear to depend on D e , IWC and the PSD shape. Optical property parameterizations in climate models and remote sensing algorithms based on historical PSD measurements may exhibit errors due to previously unknown PSD errors (i.e. the presence of ice artifacts due to the shattering of larger ice particles on the probe inlet tube during sampling). More recently developed cloud probes are designed to mitigate this shattering problem. Using realistic PSD shapes for a given temperature (and/or IWC) and cloud type may minimize errors associated with PSD shape in ice optics parameterizations and remote sensing algorithms. While this topic was investigated using two ice optics schemes (the Yang et al., 2005 database and the modified anomalous diffraction approximation, or MADA), a physical understanding of the limitations of the D e -IWC assumption was made possible by using MADA. MADA allows one to approximate the contribution of photon tunneling to absorption relative to other optical processes, which reveals that part of the error regarding the D e -IWC assumption can be associated with tunneling. By relating the remaining error to the radiation penetration depth in bulk ice (Δ L ) due to absorption, the domain where the D e -IWC assumption is weakest was described in terms of D e and Δ L .
使用中纬度冰水含量、体积消光系数和总太阳光学深度的原位估计来测试卷云冰晶的集合模型
DOI：
10.1016/j.jqsrt.2009.02.021
发表时间：
2009
影响因子：
2.3
作者：
Baran A
通讯作者：
Baran A