Saltation of snow

Abstract

Saltation of snow, the transport of snow in periodic contact with and directly above the snow surface, is governed by the atmospheric shear forces applied to the erodible snow surface, the nonerodible surface, and the moving snow particles. Empirical data measured over a snow-covered plain suggest functions for parameters important to the apportionment of atmospheric shear forces; the aerodynamic roughness height during saltation, the mean horizontal velocity of saltating particles, and the efficiency of the saltation process. The resulting mass transport expression shows an approximately linear increase in snow saltation transport rate with friction velocity, in agreement with the measurements presented. The expression is sensitive to the cohesion of the snow surface, as indexed by the threshold wind speed, that wind speed at which transport ceases; for wind speeds well above the threshold condition, higher threshold wind speeds correspond to higher transport rates. An adaptation of the expression allows calculation of the mass concentration of saltating snow from measured data and the transport rate of saltating snow from the mean wind speed at 10 m height. Application of the transport rate expression using measured wind speeds, directions, and weather observations demonstrates that the directional component of annual saltating snow transport does not always correspond with wind direction frequency. INTRODUCTION Redistribution of surface snow by wind transport signifi-cantly affects the winter microclimate, snow cover accumulation, and hence snowmelt runoff patterns in cold, windswept regions. Several authors suggest that a large component of the mass flux of wind-transported snow travels in saltation, which is the horizontal movement of particles in curved trajectories, which are near to and periodically impact the surface [Dyunin, 1967; Male, 1980; Schmidt, 1986]. Saltating snow particles are ice particles changing in form from both sublimation and abrasion. $chmidt's [1981] observations show particles approximating spheroids with mean diameters of 200 /am, and a range of diameters from approximately 10/xm to several hundred micrometers. They are assumed to have the density of ice. Saltating snow differs significantly from saltation of other materials in that the "bed" is not a layer of rounded particles but is a cohesive matrix of bonded crystals which are metamorphosed by the impact of saltating particles and the vapor transfer during ventilation. Saltating snow particles are derived from shattered surface snow crystals, and Schmidt [1980] has shown that the intercrystal bond strength, "cohesion," is a much more important parameter than crystal size in calculating the force required to eject a crystal. Particle impact is expected to result in rebound, with a shattering and reestablishment of bonds in the matrix and a "splashing" of crystals from the matrix. Schmidt, 1986] link greater cohesion to higher threshold wind speeds for transport. The threshold wind speed indexes the atmospheric shear stress not av...

Inhomogeneous precipitation distribution and snow transport in steep terrain

“…In this transport mode the snow grains follow ballistic trajectories and return to the surface, possibly rebounding or ejecting other grains. For the mass flux in saltation, many investigators [Bagnold, 1941;Takeuchi, 1980;Pomeroy and Gray, 1990] have made efforts to find empirical relations based on measurements and physical considerations. Only more recently, numerical models have been developed [McEwan and Willets, 1991;Shao and Li, 1999;Nemoto and Nishimura, 2004] which take into account the microscopic processes of aerodynamic entrainment, particle-bed collisions, particle motion and particlewind feedback.…”

Hydrologic vulnerability to climate change of the Mandrone glacier (Adamello-Presanella group, Italian Alps)

“…The retreat of Alpine glaciers has been proved with direct measurement of their annual mass balances since the 1960s, as reported for instance by Kaser et al [47]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 …”

“…The mean bias of simulated vs. measured ablation in the July to August monitoring period was -2% and the RMSE was 159 mm compared to a mean measured value of 848 mm. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 …”

“…To consider the effect of avalanches and gravitational snow transport [11] a 5% increase of the interpolated snow water equivalent was adopted, as estimated on the basis of the area of the steepest mountain slopes surrounding the glacier. The influence of snow transport by wind [22,50,65] was neglected, instead. Summer specific mass balance from the 1 st of April to the 30 th of September of each year, was computed, instead, by simulation of the mass and energy balance with the distributed hydrological model PDSLIM (Fig.…”

High resolution snow distribution data from complex Arctic terrain: a tool for model validation

“…The detailed study of drifting snow showed that saltation and suspension are the major transport modes (Budd et al, 1966;Pomeroy and Gray, 1990). The wind has to reach a certain threshold velocity before the snow particles loosen from the surface (Schmidt, 1980).…”