Swell dissipation by induced atmospheric shear stress

Type Article
Date 2014-10-06
Language English
Author(s) Perignon Yves1, Ardhuin FabriceORCID2, Cathelain M.1, Robert M.1
Affiliation(s) 1 : Ecole Centrale de Nantes, Lab Hydrodynam Energet & Environm Atmospher, Nantes, France.
2 : CNRS, IFREMER, Lab Oceanog Spatiale, Brest, France.
Source Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-10-06 , Vol. 119 , N. 10 , P. 6622-6630
DOI 10.1002/2014JC009896
WOS© Times Cited 8
Keyword(s) swell, dissipation, shear, turbulent
Abstract Observations of swell dissipation across oceans reveal a significant loss of energy that can be the result of many of processes. Among these candidate mechanisms, this paper examines the properties of the viscous air-sea boundary layer driven by swells in order to characterize the induced atmospheric flow regime and its associated viscous dissipation over swells. A series of 3-D numerical experiments is carried out with a RANS model and appropriate turbulence closure. These experiments reveal a laminar to turbulent transition in the near free-surface region for a common range of characteristic amplitudes and periods of swells under stationary conditions. At low Reynolds number, laminar conditions prevail and computed decay rates conform to the analytical formulation μν of the Stokes interfacial boundary layer for this problem. The turbulent regimes are characterized as well, and the new decay rates follow a nondimensional relation [inline image] above [inline image] (e.g., amplitude larger than 1.1 m for a 14 s monochromatic wave period). Typical decay rates are up to 4 times above the laminar values, which is a factor 10 less than the largest rates estimated for oceanic conditions. A sensitivity analysis is finally conducted to evaluate the influence of the stationary hypothesis. It demonstrates a short setup length and low relative variations of the unsteady decay rates for laminar, transitioning and developed turbulent conditions, which confirms the evaluation of steady decay rates.
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