Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy
Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy
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DOI：
10.5194/tc-8-2255-2014
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发表时间：
2014-01-01
期刊：
影响因子：
5.2
通讯作者：
du Roscoat, S. Rolland
中科院分区：
文献类型：
--
作者：
Calonne, N.;Flin, F.;du Roscoat, S. Rolland
我们开展了一项研究，以监测温度梯度变质过程中雪的微观结构和物理性质随时间的演变：将雪板在冷室中沿垂直方向承受恒定温度梯度3周，并定期采样，以便使用X射线显微断层扫描获得一系列三维（3-D）图像。然后根据这一系列 3D 图像计算出大量属性：密度、比表面积、相关长度、平均曲率和高斯曲率分布、空气和冰的曲折度、有效导热率和固有渗透率。只要有可能，就特别注意评估沿垂直和水平方向的这些特性，并推导出定义为垂直值与水平值之比的各向异性系数。研究了这些特性的时间演化及其各向异性系数，表明在实验过程中出现了强烈的各向异性行为。然后，将大部分计算出的雪物理特性与基于雪密度的两种分析估计（自洽估计和球体稀层）进行比较，并通过相关长度确定微观结构的尺寸和各向异性。这些模型只需要基本的微观结构信息，无需任何拟合参数即可为我们的实验提供相当好的性能和各向异性系数估计。我们的结果强调了微观结构和物理特性之间的相互作用，表明仅使用密度等各向同性参数无法准确描述受到温度梯度影响的雪的物理特性，需要更精细的信息。此外，这项研究构建了温度梯度下雪特性演变的详细数据库，可以用作微观或宏观尺度的雪变质作用模型的指导和验证工具。
We carried out a study to monitor the time evolution of microstructural and physical properties of snow during temperature gradient metamorphism: a snow slab was subjected to a constant temperature gradient in the vertical direction for 3 weeks in a cold room, and regularly sampled in order to obtain a series of three-dimensional (3-D) images using X-ray microtomography. A large set of properties was then computed from this series of 3-D images: density, specific surface area, correlation lengths, mean and Gaussian curvature distributions, air and ice tortuosities, effective thermal conductivity, and intrinsic permeability. Whenever possible, specific attention was paid to assess these properties along the vertical and horizontal directions, and an anisotropy coefficient defined as the ratio of the vertical over the horizontal values was deduced. The time evolution of these properties, as well as their anisotropy coefficients, was investigated, showing the development of a strong anisotropic behavior during the experiment. Most of the computed physical properties of snow were then compared with two analytical estimates (self-consistent estimates and dilute beds of spheroids) based on the snow density, and the size and anisotropy of the microstructure through the correlation lengths. These models, which require only basic microstructural information, offer rather good estimates of the properties and anisotropy coefficients for our experiment without any fitting parameters. Our results highlight the interplay between the microstructure and physical properties, showing that the physical properties of snow subjected to a temperature gradient cannot be described accurately using only isotropic parameters such as the density and require more refined information. Furthermore, this study constitutes a detailed database on the evolution of snow properties under a temperature gradient, which can be used as a guideline and a validation tool for snow metamorphism models at the micro- or macroscale.