Measurements of Drag Coefficients and Roughness Length at a Sea-Beach Interface

H. F. Vugts Institute of Earth Sciences, Department of Meteorology, Free University Amsterdam, The Netherlands

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F. Cannemeijer Institute of Earth Sciences, Department of Meteorology, Free University Amsterdam, The Netherlands

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Abstract

During unstable conditions the drag coefficient of the surf zone and the roughness length of a sand beach have been measured. It is concluded from ∼100 half-hour profiles that the drag coefficient under unstable conditions over the surf zone is the same as over the ocean. For wind speeds <6 m s−1 the roughness length of a sand beach is of the same order of magnitude as for the surf zone. For wind speeds >8 m s−1 the roughness length of a sand beach is ∼10 times higher than the value measured below 6 m s−1. This jump is related to aeolian sand transport at high wind speeds.

Abstract

During unstable conditions the drag coefficient of the surf zone and the roughness length of a sand beach have been measured. It is concluded from ∼100 half-hour profiles that the drag coefficient under unstable conditions over the surf zone is the same as over the ocean. For wind speeds <6 m s−1 the roughness length of a sand beach is of the same order of magnitude as for the surf zone. For wind speeds >8 m s−1 the roughness length of a sand beach is ∼10 times higher than the value measured below 6 m s−1. This jump is related to aeolian sand transport at high wind speeds.

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