Item: Particle size dependence of horizontal snow mass flux in drifting snow
Title: Particle size dependence of horizontal snow mass flux in drifting snow
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: Konosuke Sugiura and Norikazu Maen, Frontier Observational Research System for Global Change, Tokyo, Institute of Low Temperature Science, Hokkaido University, Sapporo
Abstract: For understanding the drifting snow structure on sattating particles with particle size distribution over the loose surface, wind tunnel experiments were carried out at friction velocities, U., 0.15, 0.23,0.30,0.39 ms-1 (reference wind speeds of 4,6,8, 10 ms-1). The air temperature was kept at -15-e' to avoid rapid sintering between snow particles. Disintegrated particles of natural compact snow, an arithmetical mean of which was 0.36 mm, were used. The number flux of drifting snow particles was measured with a snow particle counter at the leeward end at five heights of 16, 21, 31, 41 and 61 mm above the snow surface. The horizontal snow mass flux of each particle diameter, qd' decreased exponentially with increasing height, and could be described as qd=Adexp(-Bdz), where z is the height, Act is the horizontal snow mass flux of each particle diameter at the surface (z = 0), and Bdis the gradient of flux decay of each particle diameter. The reciprocal of Bd is a measure of saltation height at each particle diameter. The obtained results are as follows: (1) Ad increased with increase in particle diameter and friction velocity in general. The dependence on friction velocity varied with particle diameter, that is Ad increased with friction velocity at larger particles, but at smaller particles Ad was independent of friction velocity due to random turbulence effects. (2) A dimensionless parameter of each particle diameter, ~, was introduced as ~=Bd/(U.2/2gt1, where g is the acceleration due to gravity, and (u.2/2g) is the scaling height. ~ was independent of friction velocity at larger particles, and approached a constant value 0.1-0.3 (~==0.2) characterizing the saltation height. This indicates that we can estimate a universal height (==5(u.2/2g)) at which the horizontal mass flux virtually diminishes in a saltation layer. (3) The total snow transport rate, Qd' was calculated at each particle diameter by integrating qd from the surface to the infinity. The dimensionless total snow transport rate of each particle diameter, QdgPa-1u.-3, where Pa is the density of air, varied with increasing particle diameter, and was found to increase more rapidly than the theoretical estimates by Bagnold (1941) and Owen (1964).
Keywords: drifting snow, wind tunnel, saltation, mass flux
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