Analytical and experimental study of radiation-recrystallized near-surface facets in snow
Morstad, Blake Walden
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A 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.