Saltation-layer structure of drifting snow observed in wind tunnel

Abstract

Abstract The saltation-layer structure of drifting snow was investigated using the wind tunnel in a cold room. Experiments were conducted under various snow-temperature and wind-speed conditions over loose and hard snow covers. Snow was seeded at the upwind end of the wind tunnel. Mass-flux profiles of drifting snow were measured with a snow-particle counter. The theoretical expression for the mass flux of saltating sand (Kawamura, 1948) was fitted to the measured profiles, and two parameters in the theoretical expression, saltation height h 0 and mass flux at the surface q 0 , were determined. The main results are as follows: (1) In the case of hard snow cover, snow particles are hardly ejected and drifting snow is maintained by the seeded snow. The value of h 0 linearly increases with wind speed and decreases with snow temperature, and q 0 decreases with wind speed and is in proportion to seeding rate. (2) In the case of loose snow cover, erosion occurs under high-wind conditions and the contribution of the ejected snow particles to drifting snow is remarkable. The h 0 linearly increases with wind speed, but its value is smaller than the value over hard snow cover. Due to erosion, q 0 increases with wind speed. Snowdrift transport rate and q 0 do not change with seeding rate under low-wind conditions, because the drifting snow is saturated. Under high-wind conditions, however, both snowdrift transport rate and q 0 slightly increase with seeding rate.