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  4. The Importance of Near-Surface Winter Precipitation Processes in Complex Alpine Terrain
 
research article

The Importance of Near-Surface Winter Precipitation Processes in Complex Alpine Terrain

Gerber, Franziska  
•
Mott, Rebecca
•
Lehning, Michael  
2019
Journal of Hydrometeorology

In this study, near-surface snow and graupel dynamics from formation to deposition are analyzed using WRF in a large-eddy configuration. The results reveal that a horizontal grid spacing of ≤50 m is required to resolve local orographic precipitation enhancement, leeside flow separation, and thereby preferential deposition. At this resolution, precipitation patterns across mountain ridges show a high temporal and spatial variability. Simulated and observed event-mean snow precipitation across three mountain ridges in the upper Dischma valley (Davos, Switzerland) for two precipitation events show distinct patterns, which are in agreement with theoretical concepts, such as small-scale orographic precipitation enhancement or preferential deposition. We found for our case study that overall terrain–flow–precipitation interactions increase snow accumulation on the leeward side of mountain ridges by approximately 26%–28% with respect to snow accumulation on the windward side of the ridge. Cloud dynamics and mean advection may locally increase precipitation on the leeward side of the ridge by up to about 20% with respect to event-mean precipitation across a mountain ridge. Analogously, near-surface particle–flow interactions, that is, preferential deposition, may locally enhance leeward snow precipitation on the order of 10%. We further found that overall effect and relative importance of terrain–flow–precipitation interactions are strongly dependent on atmospheric humidity and stability. Weak dynamic stability is important for graupel production, which is an essential component of solid winter precipitation. A comparison to smoothed measurements of snow depth change reveals a certain agreement with simulated precipitation across mountain ridges.

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Type
research article
DOI
10.1175/JHM-D-18-0055.1
Author(s)
Gerber, Franziska  
Mott, Rebecca
Lehning, Michael  
Date Issued

2019

Published in
Journal of Hydrometeorology
Volume

20

Start page

177

End page

196

Subjects

Atmosphere

•

Cool season

•

Orographic effects

•

Small scale processes

•

Topographic effects

•

Snowfall

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
CRYOS  
Available on Infoscience
March 1, 2019
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/154988
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