Item: Modeling variation of surface hoar and radiation recrystallization across a slope
Title: Modeling variation of surface hoar and radiation recrystallization across a slope
Proceedings: International Snow Science Workshop, Davos 2009, Proceedings
Authors: E. Adams, L. McKittrick, A. Slaughter, P. Staron, R. Shertzer, D. Miller, T. Leonard, D. McCabe, I. Henninger, D. Catharine, M. Cooperstein and K. Laveck, Department of Civil Engineering, Montana State University, Bozeman, MT USA 59717
Abstract: Faceted ice crystals (plane faced grains) are frequently observed in investigations of slab snow avalanches. Morphologies of this sort can develop while near the snow surface. When subsequently buried, these faceted crystals may form a weak interface layer leading to an avalanche. For this reason, researchers at Montana State University in collaboration with snow safety personnel from the Yellowstone Club Ski Patrol have been investigating environmental conditions associated with near surface metamorphism. Two meteorological stations were used to correlate conditions with daily observations of grain structure at the snow surface. The field sites, one with a northern the other with a southern exposure, are meadows of 30o slope surrounded by trees and rock. In addition, radiation recrystallization and surface hoar morphologies have been replicated in the laboratory by simulating natural conditions. An energy balance model was used to estimate variations in near surface temperature conditions. LIDAR data was used to produce digital elevation maps at a one meter spatial scale. The model accounts for thermal properties of the vegetation and rock outcropping as well as snow, sun position, shadowing and surface to surface or surface with sky radiation. The modelling emphasis presented is on days when radiation recrystallization and surface hoar were observed. Based on field and laboratory results metamorphic development is assumed to be driven by the magnitude of the near surface temperature gradient in the case of radiation recrystallization and mass deposition for that of surface hoar. Calculation of these indicators reveals a spatial variation in the metamorphism across the slopes.
Keywords: snow, metamorphism, near surface faceting, surface hoar
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