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Browsing by Author "Greene, Ethan M., author"

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    Simulation of alpine snow distributions in the northern Colorado Rocky Mountains using a numerical snow-transport model
    (Colorado State University. Libraries, 1999) Greene, Ethan M., author
    Two methodologies for simulating winter snow distributions in alpine terrain are presented. First, a numerical snow-transport model (SnowTran-3D) is driven from direct meteorological observations, and second, SnowTran-3D is driven from a regional atmospheric model (ClimRAMS). In each case the simulated snow distributions are compared to observed snow depth transects within two alpine sites in the Northern Colorado Rocky Mountains, Rocky Mountain National Park, and Medicine Bow Mountains. The atmospheric conditions at these sites are characterized by persistent westerly winds with average speeds of 13 m/s, which is significantly greater than the threshold for snow transport (approximately 5 m/s). Consequently, snow redistribution by wind is the dominate component in this environment. Drift features in these areas form around rocks, alpine vegetation, and small and large topographic variations. The model successfully simulated the large-scale snow drifts, but due to the relatively coarse resolution of the vegetation and topographic data inputs (30 m), the model was unable to reproduce some of the smaller scale snow drift features. The model built large drifts in the upper regions of the east facing cirques in Rocky Mountain National Park, in regions where large perennial snow fields are observed. The model results support the theory that snow transport by wind is an important factor in sustaining these snow fields.
  • Thumbnail Image
    ItemOpen Access
    Simulation of alpine snow distributions in the northern Colorado Rocky Mountains using a numerical snow-transport model
    (Colorado State University. Libraries, 1999) Greene, Ethan M., author
    Two methodologies for simulating winter snow distributions I alpine terrain are presented. First, a numerical snow-transport model (SnowTran-3D) is driven from direct meteorological observations, and second, SnowTran-3D is driven from a regional atmospheric model (ClimRAMS). In each case the simulated snow distributions are compared to observed snow depth transects within two alpine sites in the Northern Colorado Rocky Mountains, Rocky Mountain National Park, and Medicine Bow Mountains. The atmospheric conditions at these sites are characterized by persistent westerly winds with average speeds of 13 m/s, which is significantly greater than the threshold for snow transport (approximately 5 m/s). Consequently, snow redistribution by wind is the dominate component in this environment Drift features in these areas form around rocks, alpine vegetation, and small and large topographic variations. The model successfully simulated the large-scale snow drifts, but due to the relatively coarse resolution of the vegetation and topographic data inputs (30 m), the model was unable to reproduce some of the smaller scale snow drift features. The model built large drifts in the upper regions of the east facing cirques in Rocky Mountain National Park, in regions where large perennial snow fields are observed. The model result support the theory that snow transport by wind is an important factor in sustaining these snow fields.
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    ItemOpen Access
    The thermophysical and microstructural effects of an artificial ice layer in natural snow under kinetic growth metamorphism
    (Colorado State University. Libraries, 2007) Greene, Ethan M., author; Smith, Freeman, advisor; Elder, Kevin, advisor
    The macrostructure of a seasonal snow cover evolves with each new weather event. With wind and precipitation, layers of snow coat the old snow surface and the microstructure within these layers develops as a function of the environmental conditions. The thermal, mechanical and optical properties of snow are highly dependent on its microstructure. Many researchers have investigated metamorphism in homogenous snow, but little is known of snow metamorphism at the interface of two layers. In this study I observe the thermal and microstructural evolution of layered and non-layered samples of natural snow in kinetic growth metamorphism. The layered samples contain a 4 mm thick ice layer, which creates a large gradient in thermal conductivity and porosity. I collected samples of natural snow with a density range of 150-290 kg m-3 from the mountains of northern Colorado. In a cold laboratory, I subjected paired, treatment (layered) and control (non-layered), samples to a vertical temperature gradient of 60-110 K m-1 for a period of 5 days. During the experiment I measured the heat flux at the boundaries and the temperature profile within the sample. At the end of each experiment I cast the snow samples and performed serial sectioning and three-dimensional reconstruction of the snow microstructure. I also used the thermophysical data and microstructural data to simulate the evolution of the microstructure and the thermal state at the end of the experiment. The temperature profiles show snow in a steady-state thermal environment. There is no consistent signal from the ice layer in the temperature data. The microstructure within the snow samples undergoes a dramatic change during the experiments. In the control samples vertical chains of faceted and hollow particles develop and are responsible for transporting most of the thermal energy in the sample. Faceted structures grow off the bottom of the ice layer, while the upper surface erodes and becomes smooth and round. The presence of the ice layer affects thermal, mechanical and optical properties of the snow, these effects occur within several particles of the interface and would be difficult to detect with standard field techniques.