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

Montana State University, Bozeman MT

Investigators

Abstract

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.