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The Relationship of Near‐Surface Flow, Stokes Drift and the Wind Stress
Author(s) -
Clarke Allan J.,
Van Gorder Stephen
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc014102
Subject(s) - stokes drift , stokes number , swell , stokes wave , physics , buoy , wind stress , eulerian path , mechanics , surface wave , geology , breaking wave , atmospheric sciences , optics , wave propagation , turbulence , thermodynamics , lagrangian , mathematical physics , oceanography , reynolds number
Abstract Many years of simultaneous hourly buoy wind and directional wave spectra data in the Gulf of Mexico and the Pacific were used to estimate Stokes drift and u * e w where u * = (magnitude of the local windstress/water density) 1/2 and e w is a unit vector in the direction of the local wind. Stokes drift and u * e w were strongly vectorally correlated, the two vectors on average being within a few degrees of one another. This result remained valid even when there was evidence of remotely forced swell. Extension of the observed wave spectra above 0.35 Hz to the u * ‐dependent wave breaking frequency shows that typically the e ‐folding scale of the Stokes drift with depth is less than 1.8 m, much smaller than the Ekman layer e ‐folding scale. Therefore, there is negligible induced Eulerian cancellation of the Stokes drift, and the surface particle movement is governed by the Eulerian velocity + | u Stokes | e w . Taking into account wave spreading, | u Stokes | typically ranges from about 3 to 13 cm/s. Thus, the Stokes drift, which can be estimated directly from the wind stress, is an order one contributor to the surface transport of particles.