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Terrain and drift influences on snow surface aerodynamics
A. Clifton1, K. C. Leonard1, C. Manes2, M. Lehning1.
1. SLF Davos, Switzerland2. Politecnico di Torino, Turin, Italy
AGU Fall Meeting 2010C11C-02
Surface aerodynamics
• Interaction of boundary layer and surface
• Log law framework– Friction velocity (m/s)– Roughness length (m)
0.5 1 1.5 2 2.5 3 3.5 4 4.50
0.5
1
1.5
2
2.5
0.3 m/s, 1 mmIncreased friction velocity (0.5 m/s)Increased roughness (10 mm)Both increase (0.5 m/s, 10 mm)
Speed [m/s]
Z [m]
Relevant processes
Anything that alters momentum transfer• Drift• Crystal structure• Snow metamorphosis• Surface forms• Local terrain
Wind tunnel measurements
Wind tunnel measurements
Wind tunnel measurements
Clifton, A., Rüedi, J.-D., Lehning, M. (2006).Snow saltation threshold measurements in a drifting snow wind tunnel.J. Glaciol., 52(179), 585-596. DOI: 10.3189/172756506781828430
Alpine test site measurements
• Fluxes of momentum, heat and water vapour– Sonic anemometer and
fast hygrometer– Concurrent surface
observations– 3 months of
observations– 5m measurement height
Stössel, F., M. Guala, C. Fierz, C. Manes, and M. Lehning (2010)Micrometeorological and morphological observations of surface hoar dynamics on a mountain snow cover.Water Resour. Res., 46, W04511. DOI: 10.1029/2009WR008198.
Alpine test site measurements
• Fluxes of momentum, heat and water vapour– Sonic anemometer and
fast hygrometer– Concurrent surface
observations– 3 months of
observations– 5m measurement height
Davos 3 km
Stössel, F., M. Guala, C. Fierz, C. Manes, and M. Lehning (2010).Micrometeorological and morphological observations of surface hoar dynamics on a mountain snow cover.Water Resour. Res., 46, W04511. DOI: 10.1029/2009WR008198.
Alpine test site measurements
• Fluxes of momentum, heat and water vapour– Sonic anemometer and
fast hygrometer– Concurrent surface
observations– 3 months of
observations– 5m measurement height
Davos 3 km
Stössel, F., M. Guala, C. Fierz, C. Manes, and M. Lehning (2010).Micrometeorological and morphological observations of surface hoar dynamics on a mountain snow cover.Water Resour. Res., 46, W04511. DOI: 10.1029/2009WR008198.
Williams Field, Antarctica
Williams Field, Antarctica
Commercial widget counter
York U. particle counter(P. Taylor)
Williams Field, AntarcticaWillie Field AWSAntarctic Automatic Weather Station Program AMRC, SSEC, UW-Madison
Williams Field, Antarctica
Role of snow structure
Clifton, A., C. Manes, J.-D. Ruedi, M. Guala, and M. Lehning (2008)On shear-driven ventilation of snow. Boundary-Layer Meteorol., 126, 249-261.
DOI: 10.1007/s10546-007-9235-0.
Images courtesy M. Schneebeli, SLF
1 mm
New snow Polyester foam
Results
Wind tunnel, without drift
Results
Hydraulically smooth wall
Wind tunnel (no drift)
Results
Wind tunnel, sustained drift
Wind tunnel (no drift)
Smooth wall
Results
Drifting sand, soil, waves over open water (Owen, 1960)
Wind tunnel (no drift)
Smooth wall
Wind tunnel (drift)
Results
William Field, without drift
Wind tunnel (no drift)
Smooth wall
Wind tunnel (drift)
Drifting sandand soil
Results
Williams Field, with sustained drift(neutral conditions only)
Wind tunnel (no drift)
Smooth wall
Wind tunnel (drift)
Drifting sandand soil
Williams Field(no drift)
Results
Alpine test site, all data(neutral conditions & NW flows only)
Wind tunnel (no drift)
Smooth wall
Wind tunnel (drift)
Drifting sandand soil
Williams Field(no drift)
Williams Field (drift)
Results
Revised Davenport ClassificationDavenport (2000)
Wind tunnel (no drift)
Smooth wall
Wind tunnel (drift)
Drifting sandand soil
Williams Field(no drift)
Williams Field (drift)
Alpine Site(all data)
ResultsDavenport
Classification
Wind tunnel (no drift)
Smooth wall
Wind tunnel (drift)
Drifting sandand soil
Williams Field(no drift)
Williams Field (drift)
Alpine Site(all data)
Conclusions
• Log law is a useful analogy near the ground
Conclusions
• Log law is a useful analogy near the ground• Roughness length of ‘snow’ is a function of– Friction velocity– Drift rates (increase or decrease)– Surface features (increase)– Fetch (increase)
Conclusions
• Log law is a useful analogy near the ground• Roughness length of ‘snow’ is a function of– Friction velocity– Drift rates (increase or decrease)– Surface features (increase)– Fetch (increase)
• Next steps– Wind and drift profiles coupled with surface
characterization