Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Metamorphism of dry snow as a result of temperature gradient and excess vapor density(Montana State University - Bozeman, College of Engineering, 1982) Adams, Edward EaganA heat conduction equation to determine the temperature profile in a snowpack is developed. The magnitude of temperature gradient tends to increase as the snow surface is approached, with local minimums through high snow density layers and local maximums above and below these layers. Calculations are made which determine the excess vapor density over the ice grain surfaces which border the pore space. In the presence of a temperature gradient faceted crystals will develop near the top of the pore, as ice is sublimated off of the surfaces in the lower region. Necks will deteriorate most readily, causing an overall weakening of the snowpack. There will be a reduction in the percentage of rounded grains as the faceted form develops. The process is enhanced at warmer temperature and larger temperature gradients. Temperature and excess vapor density are known to determine the habit of ice crystals grown in air. The model predicts excess vapor densities in the snowpack which are similar to those which exist in the atmosphere. Comparison of crystal habits predicted by the model are in good agreement with experimental evidence, when the pore geometry and temperature conditions are specified.Item Analytical and experimental study of radiation-recrystallized near-surface facets in snow(Montana State University - Bozeman, College of Engineering, 2004) Morstad, Blake Walden; Chairperson, Graduate Committee: Edward E. AdamsA study on the formation of radiation recrystallized near-surface facets in snow was performed experimentally in an environmental chamber. This recrystallization occurs when surface snow metamorphoses into faceted crystals that result from absorbed solar radiation coupled with cooling effects from longwave and turbulent fluxes. The environmental chamber utilized a metal-halide lamp to mimic solar radiation, which penetrates the snow adding thermal energy at depth. In addition, the ceiling was cooled to simulate a cold sky, thus inducing a net longwave radiation loss at the snow surface. Turbulent flux parameters, including relative humidity and wind velocity were measured. Forty-centimeter thick snow samples with insulated sides were placed in the -10 C chamber on a constant temperature plate also at -10 C. The study focused on the significance of radiation balance and snow density on the recrystallization of snow near the surface. Imposed constant boundary conditions led to formation of facets of varying size at and near the snow surface. Faceting was observed when applied solar flux between 350 - 1100W/m2 was combined with longwave and turbulent exchange for snow with densities below 300 kg/m3. To better understand the governing processes and to extend the number of scenarios a thermodynamic model was used to extrapolate upon the experimental results. The model incorporated meteorological inputs and calculated a snowpack temperature profile based on relevant snow parameters. Conclusions from both experimental and model analysis show radiation and snow density to be significant factors in radiation recrystallized near-surface facets.