Direct Measurement Of Shear Stress During Snow Saltation

Abstract

Wind-tunnel experiments were carried out to measure the shear stressduring snow saltation. Shear stress acting on the snow surface, measured directly with a newly developed drag meter system, revealedthat the shear stress increased with the development ofsaltation. This result supports Owen's hypothesis that the saltationlayer acts as an increased roughness to the flow above the saltationlayer, leading to an increase in surface shear stress. To investigate the contribution of the grain borne shear stressτg and the fluid shear stress τf to the increment of the total shear stress τtotal, τg was calculated from the loss of horizontal momentum of saltating snowparticles. Since τg is the largest contribution to theincrement of τtotal, the collision of thesaltating particles is dominant for the shear stressmodification. The results qualitatively support the numericalsimulation reported by McEwan and Willetts.