High Frequency Near-Surface Snow Transport Response to Alpine Turbulence

Blowing snow is a temporally variable natural process closely coupled with atmospheric boundary layer (ABL) turbulence that influences the volume, rate, and location of spring snowmelt runoff, as well as the growth and ablation of small mountain glaciers. However, relating snow transport to ABL turbulence is increasingly difficult as snow behaves as inertial particles near the surface that do not follow wind streamlines, redistributing wind kinetic energy through particle transport and bed collision. Including blowing snow in hydrological and atmospheric models in cold regions and mountainous terrain requires a clear knowledge of the scales of turbulence relevant to snow transport at the snow surface, the active region of snow erosion and deposition. Snow entrainment and transport responds to wind fluctuations on sub-second timescales, and upscaling to coarser temporal and spatial scales is problematic, especially in complex terrain.

This research focuses on quantifying the importance of high frequency gusts to blowing snow transport near the snow surface. A field experiment in the Canadian Rockies has collected high frequency snow particle motion data using high-speed photography of a laser-illuminated cross section of blowing snow. This novel approach is supplying data capable of bridging the gap between high frequency wind events and snow particle response through Particle Tracking Velocimetry (PTV). Compared against 3D sonic anemometer wind measurements, eddy structures relevant for snow transport have been investigated. The role of different quadrant generators of surface Reynolds stress as well as the spectral coherence between wind and blowing snow signals are examined. It appears that sweep events are extremely important in initiating erosion of snow particles from the snowpack.