Boundary-Layer Meteorology

, Volume 148, Issue 1, pp 195–206 | Cite as

Field Evidence for the Upwind Velocity Shift at the Crest of Low Dunes

Article

Abstract

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.

Keywords

Dunes Flow over a hill Turbulence Velocity shift 

Notes

Acknowledgments

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.

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Laboratoire de Physique et Mécanique des Milieux Hétérogènes (PMMH)UMR 7636, CNRS, ESPCI, Univ. Paris Diderot, Univ. P.M. CurieParisFrance
  2. 2.School of Geography and the EnvironmentOxford University Centre for the EnvironmentOxfordUK

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