10.3 Intermittency of Aeolian Snow Transport and its Dependence on Flow and Snow-Bed Properties

Wednesday, 22 June 2016: 4:30 PM
Bryce (Sheraton Salt Lake City Hotel)
Michael Lehning, WSL Institute for Snow and Avalanche Research SLF Davos and CRYOS EPFL, Davos Dorf, Switzerland; and E. Paterna, P. Crivelli, S. Horender, F. Comola, and M. G. Giometto

Saltation of snow is one of the fascinating physics problems, for which dynamics are almost entirely determined by fluid – solid interactions at the flow – bed interface. The fluid – particle interactions involve small scales, which may be as small as the particle diameters (10-3 m) and certainly not larger than larger turbulent eddies at the surface or streamers (10-1 m). These small-scale interactions are inaccessible to both, conventional measurement setups as well as conventional flow modeling such as RANS or LES. Yet they determine on much larger scales reaching 106 m, how large ice sheets, glaciers, snow covers and sea ice develop over time. Parameterizations of saltation using mean quantities are used in large-scale models but often lack generality given that a huge variety of drifting snow surface conditions exists. Recent progress in measurement techniques as well as numerical modeling allows a more fundamental understanding of the small-scale interaction. Therefore, this contribution shows on the basis of a combination of wind tunnel measurements with numerical modeling, how much of the intermittency of snow mass fluxes can be attributed to turbulence and how much is caused by the snow properties and a self-organization of the saltation system. The measurements reveal the existence of two regimes of interaction. A coupling of the mass flux from the wind is observed in weak saltation and an effective decoupling of the mass flux from the wind in strong saltation. Model simulations are used to show how model choices of flow – particle – bed interactions (aerodynamic entrainment, rebound, splash) influence mass flux dynamics. Limitations of current model descriptions are assessed and interpreted with respect to process representation in larger-scale models.
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