Studies of blowing snow and its impact on the atmospheric surface layer.

摘要

In January - May of 2004 as a part of the Canadian Arctic Shelf Exchange Study experiment, an on-ice camp and a meteorological measurement site were established on first-year landfast ice. Standard meteorological and turbulent flux measuring instrumentation was complimented with a set of sensors dedicated to the detection of airborne particles and measurements of various parameters of snow transport. Snow cover probing and manual observations at the ship meteorological station and on the ice were performed on schedule according to the activities plan. Photoelectric particle detectors, designed and fabricated at York University, Toronto, were installed at various heights above the snow surface and provided continuous information on snow particle flux during this period.;The aerodynamic roughness length z0 m for snow covered seasonal ice was derived from pairs of wind speed and temperature profiles measured during the experiment. Its median value is 0.001 m with variations that span two orders of magnitude. This value is valid for flow with friction velocity u* greater than 0.35 m s -1 and less than 0.7 m s-1 (maximum encountered). No dependency of roughness length on suspended snow particle density in the reported range of u* was revealed. The Maximum Likelihood approach is at the base of our profile fitting procedure. The effect of random measurement errors on the result of fitting is examined.;The quantitative assessment of the particle load in the multicomponent flow requires proper instruments to measure mass or volume fraction of individual constituents. Three generations of photo-electronic counters have been developed. The first two variants only counted particles without sizing them. The third variant has an ability to measure the time-of-flight of the particle through the sensor field of view. This time can be converted into estimates of the particle size if certain assumptions are made. Calibration procedures are developed that allow for accurate estimation of the minimum detected particle diameters depending on both the particle position in the sampling volume and its speed.;Drifting or blowing of snow in the course of the experiment was detected for 40% of the time. The criteria for blowing snow event was to last at least one hour and be separated from the previous event by greater than one hour. These criteria resulted in identification of 32 events. We propose a method of prediction of the threshold wind speed that has to be attained for blowing to begin. The method is different for three types of snow surface forming processes: solid precipitation, hoarfrost deposition and wind hardening.