Measurements Of Blowing Snow, Part Ii: Mass And Number Density Profiles And Saltation Height At Franklin Bay, Nwt, Canada

摘要

Blowing snow is a frequent and significant winter weather event, and there is currently a need for more observations and measurements of blowing snow, especially in arctic and subarctic environments. This paper is the second part in a two part series studying blowing snow in Churchill, Manitoba, and Franklin Bay, NWT. In this part, the development and use of a camera system to measure the relative blowing snow density profile near the snow surface is described. This system has been used, along with standard meteorological instruments and optical particle counters, during a field campaign at Franklin Bay, NWT. A best-fit to the mass density profile in the saltation layer is derived, assuming a half-normal distribution of the vertical ejection velocity of saltating particles. Within the saltation layer, the observed vertical profile of mass density is found to be proportional to the function exp(- 0.61z/h), where h is the average height of the saltating particles. For the range of conditions studied, h varies from 1.0 to 10.4 mm, while the extent of the saltation layer varies from 17 to over 85 mm. There is a weak correlation between h and the square of friction velocity. There are weak negative correlations between h and temperature and relative humidity. No correlation is seen between h and the snow age. At greater heights, z > 0.2 m, the blowing snow density varies according to a power law (p_s ∝ z~(- γ)), with a negative exponent 0.5 < γ < 3. Between these saltation and suspension regions, results suggest that the blowing snow density decreases following a power law with an exponent possibly as high as γ≈8.