On Shear-Driven Ventilation of Snow |
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Authors: | Andrew Clifton Costantino Manes Jean-Daniel Rüedi Michele Guala Michael Lehning |
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Institution: | (1) Swiss Federal Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, Davos Dorf, 7260, Switzerland;(2) University of Northern British Columbia, Prince George, BC, Canada |
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Abstract: | A series of experiments have been made in a wind tunnel to investigate the ventilation of snow by shear. We argue that the
zero-plane displacement can be used as a convenient indicator of ventilation, and that this can be obtained from measurements
of mean velocity profiles in conditions of zero pressure gradient. Measurements made over a natural snow surface show a zero-plane
displacement depth of less than 5 mm, but practical considerations preclude extensive use of snow for these measurements.
Instead, the influence of permeability is investigated using reticulated foams in place of snow. We demonstrate that the foam
and snow have similar structure and flow-relevant properties. Although the surface of the foam is flat, the roughness lengths
increase by two orders of magnitude as the permeability increases from 6 × 10−9 to 160 × 10−9 m2. The zero-plane displacement for the least permeable foams is effectively zero, but more than 15 mm for the most permeable
foams. Our data compare well to the few studies available in the literature. By analogy to conditions over snow surfaces,
we suggest that shear-driven ventilation of snow is therefore limited to the upper few millimetres of snow surfaces. |
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Keywords: | Boundary-layer meteorology High latitudes Porous media Snow Ventilation Zero-plane displacement |
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