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research article

Radar measurements of blowing snow off a mountain ridge

Walter, Benjamin
•
Huwald, Hendrik
•
Gehring, Josué  
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June 3, 2020
The Cryosphere

Modelling and forecasting wind-driven redistribution of snow in mountainous regions with its implications on avalanche danger, mountain hydrology or flood hazard is still a challenging task often lacking in essential details. Measurements of drifting and blowing snow for improving process understanding and model validation are typically limited to point measurements at meteorological stations, providing no information on the spatial variability of horizontal mass fluxes or even the vertically integrated mass flux. We present a promising application of a compact and low-cost radar system for measuring and characterizing larger-scale (hundreds of metres) snow redistribution processes, specifically blowing snow off a mountain ridge. These measurements provide valuable information of blowing snow velocities, frequency of occurrence, travel distances and turbulence characteristics. Three blowing snow events are investigated, two in the absence of precipitation and one with concurrent precipitation. Blowing snow velocities measured with the radar are validated by comparison against wind velocities measured with a 3D ultra-sonic anemometer. A minimal blowing snow travel distance of 60–120m is reached 10–20% of the time during a snow storm, depending on the strength of the storm event. The relative frequency of transport distances decreases exponentially above the minimal travel distance, with a maximum measured distance of 280 m. In a first-order approximation, the travel distance increases linearly with the wind velocity, allowing for an estimate of a threshold wind velocity for snow particle entrainment and transport of 7.5–8.8m/s, most likely depending on the prevailing snow cover properties. Turbulence statistics did not allow a conclusion to be drawn on whether low-level, low-turbulence jets or highly turbulent gusts are more effective in transporting blowing snow over longer distances, but highly turbulent flows are more likely to bring particles to greater heights and thus influence cloud processes. Drone-based photogrammetry measurements of the spatial snow height distribution revealed that increased snow accumulation in the lee of the ridge is the result of the measured local blowing snow conditions.

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Type
research article
DOI
10.5194/tc-14-1779-2020
Author(s)
Walter, Benjamin
Huwald, Hendrik
Gehring, Josué  
Bühler, Yves
Lehning, Michael  
Date Issued

2020-06-03

Published in
The Cryosphere
Volume

14

Start page

1779

End page

1794

Note

This work is distributed under the Creative Commons Attribution 4.0 License.

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

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Available on Infoscience
June 3, 2020
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/169072
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