Wind transport of snow

Physically-based expressions describing the flow of blowing snow are developed and presented. The equations calculate the mass transport of snow as saltating (near-surface) and suspended (above the surface) flow and the rate of sublimation of snow in transport. Measurements of the vertical gradient of blowing snow mass flux, wind-speed, air temperature and humidity in the surface boundary-layer are used to calibrate the expressions. Blowing snow mass flux is measured with an opto-electronic particle detector, developed for this study. The relationships describing saltation are developed from a steady-state balance of shear stresses exerted among the atmosphere, snow surface and particles and are calibrated using field measurements of horizontal mass flux within a few centimetres of the snow surface. The mass flux of snow transported in saltation shows an approximately linear increase with wind-speed. Steady-state turbulent diffusion theory is used to develop relationships which describe suspended blowing snow and which are calibrated from field measurements of the horizontal mass flux at heights from near the surface to two metres. The mass flux of snow transported in suspension is greater than that in saltation and shows an exponential increase with the wind-speed. Sublimation of blowing snow is calculated based on a consideration of heat and water vapour fluxes at the particle surface. Sublimation rates increase exponentially with wind-speed and increase by an order of magnitude as the air temperature increases form {dollar}-{dollar}35{dollar}spcirc{dollar}C to {dollar}-{dollar}1{dollar}spcirc{dollar}C or the relative humidity decreases from 95% to 40%.; The expressions are compiled in a mass-balance model, termed the Prairie Blowing Snow Model, which calculates the horizontal mass flux and sublimation rate of blowing snow and the erosion rate at the surface. The Model uses standard meteorological station measurements and terrain data as inputs. The unobstructed distance over which snow is transported is shown to be an important parameter affecting the surface erosion rate. For distances less than 500 m the erosion rate is controlled by the magnitude of the horizontal mass flux, while for greater distances the sublimation rate is the controlling factor.