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Dynamics of Langmuir circulation in oceanic surface layers

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dc.contributor.author Gnanadesikan, Anand
dc.date.accessioned 2012-11-19T21:22:52Z
dc.date.available 2012-11-19T21:22:52Z
dc.date.issued 1994-09
dc.identifier.uri http://hdl.handle.net/1912/5566
dc.description Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1994 en_US
dc.description.abstract This work investigates whether large-scale coherent vortex structures driven by wave-current interaction (Langmuir circulation) are responsible for maintaining the oceanic mixed layer. Langmuir circulations dominate the near-surface vertical transport of momentum and density when the characteristic scale for forcing (defined as the Craik-Leibovich instability parameter γCLS) is stronger than the characteristic scale for diffusive decay γdiff. Since the wave-current forcing is concentrated near the surface both terms depend on the cell geometry. Cells with long wavelengths penetrate more deeply into the water column. These cells grow more slowly than the fastest growing mode for most cases, but always dominate the solution in the absence of Coriolis forces. In the presence of Coriolis forces, the horizontal wavelength and thus the depth of penetration are limited. When a cell geometry is found such that γCLS » γdiff, the current profile produced by small-scale diffusion is unstable to Langmuir cells and the cells replace small-scale diffusion as the dominant vertical transport mechanism for momentum and density. The perturbation crosscell shear is predicted to scale as γCLS. Such a scaling is observed during two field experiments. The observed velocity profile during these experiments is more sheared than predicted by a model which implicitly assumes instantaneous mixing by large eddies, but less sheared than predicted by a model which assumes small-scale mixing by near-isotropic turbulence. The latter profile is unstable to Langmuir cells when waves are present. The inclusion of cells driven by wave-current interaction explains the failure of the mixed layer to restratify on two days with high waves and low wind. Wave-current interaction introduces a small but efficient source of energy for transporting density which goes as the surface stress times the Stokes drift. en_US
dc.description.sponsorship The Office of Naval Research supported me throughout graduate school, first as an ONR Graduate Fellow. and later as a research assistant under the Surface Waves Processes Program (ONR Grant N00014-90-J-1495). en_US
dc.format.mimetype application/pdf
dc.language.iso en_US en_US
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en_US
dc.relation.ispartofseries WHOI Theses en_US
dc.subject Ocean circulation en_US
dc.subject Oceanic mixing en_US
dc.title Dynamics of Langmuir circulation in oceanic surface layers en_US
dc.type Thesis en_US
dc.identifier.doi 10.1575/1912/5566


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