Item: Experimental study of radiation-recrystallized near-surface facets in snow
Title: Experimental study of radiation-recrystallized near-surface facets in snow
Proceedings: Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming
Authors: B.W. Morstad, Western Transportation Institute & Department of Mechanical Engineering, Montana State University, Bozeman, Montana, USA, E.E. Adams, L.R. McKittrick, Department of Civil Engineering, Montana State University, Bozeman, Montana, USA
Abstract: An experimental study on the formation of radiation recrystallized near-surface facets in snow was performed in an environmental chamber. This form of recrystallization occurs when surface snow metamorphoses into faceted crystals that result from absorbed solar radiation coupled with cooling effects from long wave and turbulent energy exchanges. The environmental chamber utilized a metalhalide 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 long wave 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 the 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 350−1140 W/m2 was combined with long wave and turbulent exchange for snow with densities ranging from 170 to 410 kg/m3. To better understand the governing processes and to extend the number of scenarios evaluated, 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 experimental analysis show radiation and snow density to be significant factors in radiation recrystallized near-surface facets.
Keywords: near-surface faceting, kinetic growth, metamorphism, radiation balance
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