Experimental and analytical study of radiation-recrystallized near-surface facets in snow

Radiation recrystallization occurs when surface snow metamorphoses into faceted crystals due to a radiation exchange that can occur near the surface of a snowpack. In particular, large temperature gradients and associated vapor pressure gradients can occur near the surface when absorbed solar radiation is coupled with cooling effects from longwave radiation and turbulent fluxes.An experimental study on the formation of radiation-recrystallized near-surface facets in snow was performed in an environmental chamber. A metal-halide lamp was used to mimic solar radiation, which penetrates the snow allowing thermal energy to be absorbed at depth. In addition, the ceiling was cooled to simulate a cold sky, thus inducing a net longwave radiation loss at the snow surface. Air temperature in the chamber was maintained at − 10 °C, while turbulent flux parameters, including relative humidity and wind velocity, were measured. Forty centimeter thick snow samples with insulated lateral sides were placed in the chamber on a constant temperature plate also at − 10 °C.The study focused on the significance of radiation exchange and snow density on recrystallization near the snow surface. Imposed boundary conditions led to the formation of facets of varying size at and near the snow surface. Faceting was observed when an applied solar flux between 350 and 1100 W/m2 was combined with longwave and turbulent exchanges for snow with densities ranging from 170 to 410 kg/m3.To better understand the dominant factors, a thermodynamic model was used to extrapolate from the experimental results. The model incorporated meteorological inputs and was used to calculate a snowpack temperature profile using relevant snow parameters. Both experimental and model analyses indicate that radiation exchange and snow density are significant factors in the growth of radiation-recrystallized near-surface facets in snow.