1. Terrain and drift influences on snow surface aerodynamics A. Clifton 1, K. C. Leonard 1, C. Manes 2, M. Lehning 1. 1.SLF Davos, Switzerland 2.Politecnico di Torino, Turin, Italy AGU Fall Meeting 2010 C11C-02

2. Surface aerodynamics Interaction of boundary layer and surface Log law framework – Friction velocity (m/s) – Roughness length (m)

3. Relevant processes Anything that alters momentum transfer Drift Crystal structure Snow metamorphosis Surface forms Local terrain

4. Wind tunnel measurements

6. 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

7. 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.

8. 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.

9. 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.

10. Williams Field, Antarctica

11. Commercial widget counter York U. particle counter (P. Taylor)

12. Williams Field, Antarctica Willie Field AWS Antarctic Automatic Weather Station Program AMRC, SSEC, UW-Madison

13. Williams Field, Antarctica

14. 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 snowPolyester foam

15. Results Wind tunnel, without drift

16. Results Hydraulically smooth wall Wind tunnel (no drift)

17. Results Wind tunnel, sustained drift Wind tunnel (no drift) Smooth wall

18. Results Drifting sand, soil, waves over open water (Owen, 1960) Wind tunnel (no drift) Smooth wall Wind tunnel (drift)

19. Results William Field, without drift Wind tunnel (no drift) Smooth wall Wind tunnel (drift) Drifting sand and soil

20. Results Williams Field, with sustained drift (neutral conditions only) Wind tunnel (no drift) Smooth wall Wind tunnel (drift) Drifting sand and soil Williams Field (no drift)

21. Results Alpine test site, all data (neutral conditions & NW flows only) Wind tunnel (no drift) Smooth wall Wind tunnel (drift) Drifting sand and soil Williams Field (no drift) Williams Field (drift)

22. Results Revised Davenport Classification Davenport (2000) Wind tunnel (no drift) Smooth wall Wind tunnel (drift) Drifting sand and soil Williams Field (no drift) Williams Field (drift) Alpine Site (all data)

23. Results Davenport Classification Wind tunnel (no drift) Smooth wall Wind tunnel (drift) Drifting sand and soil Williams Field (no drift) Williams Field (drift) Alpine Site (all data)

24. Conclusions Log law is a useful analogy near the ground

25. 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)

26. 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