Abstract
ABSTRACTEvery winter, snowy landscapes are smoothed by snow deposition in calm conditions (no wind). In this study, we investigated how vertically falling snow attenuates topographic relief at horizontal scales less than or approximately equal to snow depth (e.g., 0.1–10 m). In a set of three experiments under natural snowfall, we observed the particle-scale mechanisms by which smoothing is achieved, and we examined the cumulative effect at the snowpack scale. The experiments consisted of (a) a strobe-light box for tracking the trajectories of snowflakes at deposition, (b) allowing snow to fall through a narrow gap (40 mm) and examining snow accumulation above and below the gap, and (c) allowing snow to accumulate over a set of artificial surfaces. At the particle scale, we observed mechanisms enhancing (bouncing, rolling, ejection, breakage, creep, metamorphism) and retarding (interlocking, cohesion, adhesion, sintering) the rate of smoothing. The cumulative effect of these mechanisms is found to be driven by snowpack surface curvature, introducing a directional bias in the lateral transport of snow particles. Our findings suggest that better quantification of the mechanisms behind smoothing by snow could provide insights into the evolution of snow depth variability, and snow-vegetation interactions.
Highlights
Two of the most remarkable, and widely appreciated effects of snow are its ability to alter the color and the nature of the surface on which it falls
We explore the mechanisms that produce lateral movement of snow particles during natural snowfall in the absence of wind, and the resulting changes in surface geometry produced by these mechanisms as snow builds up
Kuroiwa and others (1967), reporting on their studies of the micromeritical properties of snow, examined the angle of repose of snow that had fallen vertically from a hopper. Finding that this angle increased with increasing snow temperature, they attributed the difference to increasing cohesive forces between particles produced as the liquid-like layer on the snow particles increased in thickness (Faraday, 1850; Sazaki and others, 2012)
Summary
Two of the most remarkable, and widely appreciated effects of snow are its ability to alter the color and the nature of the surface on which it falls. They had come close to an understanding that the immediate fate of a snow particle falling onto a surface is determined by a force balance between the kinetic energy of the incoming particle (A or E in Fig. 2), which is a function of its mass and velocity, its coefficient of restitution (a material property of ice), which determines if and how far it will bounce, and the cohesive and interlock forces that tend to immobilize a particle when it lands These cohesive forces are produced either by the viscous suction of the liquid-like layer (F1), the mechanical interlocking of snow particles (F2), a combination of both, or perhaps static attraction (Schmidt and others, 1999)
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