Observation and estimation of Lagrangian, Stokes and Eulerian currents induced by wind and waves at the sea surface - Archive ouverte HAL
Preprints, Working Papers, ... Year : 2009

Observation and estimation of Lagrangian, Stokes and Eulerian currents induced by wind and waves at the sea surface

Abstract

The surface current response to winds is analyzed in a two-year time series of a 12 MHz (HF) Wellen Radar (WERA) off the West coast of France. The measured currents, with tides filtered out, are of the order of 1.0 to 1.8% of the wind speed, in a direction 10 to 40 degrees to the right of the wind. This Lagrangian current can be decomposed as the vector sum of a quasi-Eulerian current U_E, representative of the top 1 m of the water column, and a part of the wave-induced Stokes drift Uss at the sea surface. Here Uss is estimated with an accurate numerical wave model, thanks to a novel parameterization of wave dissipation processes. Using both observed and modelled wave spectra, Uss is found to be very well approximated by a simple function of the wind speed and significant wave height, generally increasing quadratically with the wind speed. Focusing on a site located 100 km from the mainland, the estimated contribution of Uss to the radar measurement has a magnitude of 0.6 to 1.3% of the wind speed, in the wind direction, a fraction that increases with wind speed. The difference U_E of Lagrangian and Stokes contributions is found to be of the order of 0.4 to 0.8% of the wind speed, and 45 to 70 degrees to the right of the wind. This elatively weak quasi-Eulerian current with a large deflection angle is interpreted as evidence of strong near-surface mixing, likely related to breaking waves.
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Dates and versions

hal-00331675 , version 1 (20-10-2008)
hal-00331675 , version 2 (19-02-2009)
hal-00331675 , version 3 (02-04-2009)
hal-00331675 , version 4 (09-04-2009)

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Fabrice Ardhuin, Louis Marié, Nicolas Rascle, Philippe Forget, Aaron Roland. Observation and estimation of Lagrangian, Stokes and Eulerian currents induced by wind and waves at the sea surface. 2009. ⟨hal-00331675v4⟩
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