Field Evidence for the Upwind Velocity Shift at the Crest of Low Dunes
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Flow that is topographically forced by hills and sand dunes accelerates on the upwind (stoss) slopes and reduces on the downwind (lee) slopes. This secondary wind regime, however, possesses a subtle effect, reported here for the first time from field measurements of near-surface wind velocity over a low dune: the wind velocity close to the surface reaches its maximum upwind of the crest. Our field measurements show that this upwind phase shift of velocity with respect to topography is found to be in quantitative agreement with the prediction of hydrodynamical linear analysis for turbulent flows with first-order closures. This effect, together with sand transport spatial relaxation, is at the origin of the mechanisms of dune initiation, instability and growth.
KeywordsDunes Flow over a hill Turbulence Velocity shift
BA and PC are grateful to F. Charru for stimulating discussions. The help of H. Elbelrhiti, L. Kabiri and L. Olver has been very welcome for the field work. We thank ANR Zephyr grant \(\#\)ERCS0718 for funding.
- Benalla M, Alem M, Rognon P, Desjardins R, Hilali A, Khardi A (2003) Les dunes du Tafilalet (Maroc): dynamique éolienne et ensablement des palmeraies. Sciences et changements planétaires/Sécheresse 14:73–83Google Scholar
- McLean SR (1990) The stability of ripples and dunes. Earth Sci Rev 29:131–144Google Scholar
- Weng WS, Hunt JCR, Carruthers DJ, Warren A, Wiggs GFS, Linvingstone I, Castro I (1991) Air flow and sand transport over sand dunes. Acta Mech 2:1–22Google Scholar