Snow particle characteristics in the saltation layer

Christof Gromke,Benjamin Walter,Stefan Horender,Michael Lehning

doi:10.3189/2014jog13j079

Abstract

AbstractShadowgraphy was employed to study snow saltation in boundary-layer wind tunnel experiments with fresh, naturally deposited snow. The shadowgraphy method allowed for a temporally and spatially high-resolution investigation of snow particle characteristics within a measurement area of up to 50 mm × 50 mm. Snow particle size and number characteristics, and their variation with height in the saltation layer, were analysed. The following observations and findings were made for the saltation layer: (1) the particle number decreases exponentially with height, (2) the mean particle diameter is fairly constant, with a very slight tendency to decrease with height, (3) the maximum particle diameter decreases linearly with height, and (4) the snow particle size distribution can be adequately described by gamma probability density functions. The shape and scale parameters of the gamma distribution were found to vary systematically, though only slightly, with height over ground and between experiments with different snowpack characteristics.

Highlights

Saltation is an important transport mechanism in drifting snow and is considered to accomplish the bulk of snow mass transport (e.g. Kind, 1990)
The fraction of saltation of the total snow mass transport depends on the wind shear velocity at the surface and on the wind speed above ground
SUMMARY AND CONCLUSION Snow particle size characteristics in the saltation layer were investigated with shadowgraphy in wind tunnel experiments

Summary

Introduction

Saltation is an important transport mechanism in drifting snow and is considered to accomplish the bulk of snow mass transport (e.g. Kind, 1990). Liston and Sturm (1998) estimate that for shear velocities below $0.45 m s–1 the transport of snow by saltation is larger than that by turbulent suspension. Apart from its relative importance in the total snow mass transport and more fundamentally, saltation constitutes a lower boundary condition for drifting snow when saltating particles are entrained by turbulent eddies and enter into suspension Radok, 1968; Pomeroy, 1989; Xiao and others 2000) For this reason, insights into particle dynamics and characteristics in the saltation layer play an important role for the understanding and modelling of the snow transport in turbulent suspension

Methods

Results

Conclusion