The Influence of Atmospheric Conditions on Thermomechanical Processes and Proprieties of Snow

在陆地环境中，冰存在于其相变温度附近。因此，地面上的雪是一种热力学活性物质，具有不断变化的颗粒状结构。积雪的微观结构几乎影响了其所有的热机械和光学性能。我们将更好地确定控制近地表变质作用的耦合环境参数，并将随后的形态与雪强度(对雪崩潜力很重要)和陆地/大气界面的能量平衡联系起来。我们将把现场、实验室和数值模拟结合起来。这三个研究假设是：由于自然大气边界条件发生的微观结构变化可以在实验室环境中复制并测量得到的热力性质；雪的各向异性形态可以量化并与导热系数和力学性质有关；过程驱动的微观结构可以根据热输入推断。实地研究将在现有的两个阿尔卑斯山研究地点进行。现场气象数据将指示强加的实验室条件，以准确复制自然环境和随后的变质过程。通过模拟观测到的自然条件，将在最先进的寒冷气候模拟室中开发重要的微观结构。我们将开发辐射再结晶、表面灰化生长和昼夜再结晶的近表面变质实验方案。理论方面包括开发微结构组构张量、非平衡热力学分析变质作用和地形模拟。将导出一个组构张量来描述热力相关的各向异性方向形态，这种形态是由于变质作用而形成的。基于温度梯度引起的微观结构，我们将使用熵产生极值的概念来评估热传递。单个热传递过程(传导、扩散、对流)的贡献趋向于最有效的累积热传递(有效导热系数)。综上所述，这些技术将被用来分析和经验地量化这种热诱导的织物进化及其对雪的有效材料特性的后续影响。我们将测量热机械性能，包括导热系数、渗透阻力、剪切/正常强度和体积性能。将在实地研究中采用考虑地形和地形热物性的现有热力模型，以评估空间变异性。我们将与USFS国家雪崩中心合作，协助其向雪地安全从业者提供信息、新发展和技术的使命。此外，我们将与当地的USFS雪崩中心对接，研究如何最好地将积雪的热模拟用于实际应用。与当地滑雪区雪上安全团队的互动为这个团队提供了一个机会，让他们参与到他们感兴趣的领域的科学研究中。然后，他们将继续与该领域的同事分享他们的发现，扩大影响。

Ice exists near its phase change temperature in the terrestrial environment. Consequently, snow on the ground is a thermodynamically active material with a granular structure that is continuously changing. The snowpack microstructure influences virtually all of its thermo-mechanical and optical properties. We will better determine the coupled environmental parameters governing near surface metamorphism and tie the consequent morphology to snow strength (important to avalanche potential) and energy balance at the terrestrial/atmosphere interface. We will integrate field, laboratory and numerical modeling. The three research hypotheses are: microstructural changes that occur due to natural atmospheric boundary conditions can be replicated in a laboratory environment and the resulting thermo-mechanical properties measured; anisotropic morphology of snow can be quantified and related to thermal conductivity and mechanical properties; process driven microstructure can be deduced based on thermal input. Field studies will be carried out at two existing alpine research sites. Field meteorological data will dictate imposed laboratory conditions to accurately replicate the natural environment and consequent metamorphic processes. Important microstructure will be developed in the state-of-the-art Cold Climate Simulation Chamber through simulation of observed natural conditions. We will develop near surface metamorphism laboratory protocols for radiation recrystallization, surface hoar growth and diurnal recrystallization. Theoretical aspects include developing a microstructure fabric tensor, non-equilibrium thermodynamics analyzing metamorphism and terrain modeling. A fabric tensor to describe thermo-mechanically relevant anisotropic directional morphology, which develops due to metamorphism, will be derived. Entropy production extremum concepts will be used to evaluate heat transport based on microstructure resulting from imposed temperature gradients. The contributions of the individual heat transfer processes (conduction, diffusion, convection) tend toward the most efficient cumulative heat transport (effective thermal conductivity). Taken together, these techniques will be used to analytically and empirically quantify this thermally-induced evolution in fabric and its subsequent effect on snow's effective material properties. We will measure thermo-mechanical properties, including; thermal conductivity, penetration resistance, shear/normal strength and bulk properties. An existing thermal model accounting for topography and terrain thermal properties will be implemented in field studies to assess spatial variability. We will work with the USFS National Avalanche Center to assist its mission to provide information, new developments and technology to snow safety practitioners. Additionally we will interface with the local USFS avalanche center to investigate how best to exploit thermal modeling of the snowcover for practical application. Interaction with a local ski area snow safety team provides an opportunity for this group to be involved in a scientific study in a field in which they have an intense interest. They will then go on to share their findings with colleagues in the field, expanding the impact.