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Rapid mixed layer depening by the combination of Langmuir and shear instabilities : a case study

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dc.contributor.author Kukulka, Tobias
dc.contributor.author Plueddemann, Albert J.
dc.contributor.author Trowbridge, John H.
dc.contributor.author Sullivan, Peter P.
dc.date.accessioned 2010-12-29T15:15:27Z
dc.date.available 2011-05-01T08:24:37Z
dc.date.issued 2010-11
dc.identifier.citation Journal of Physical Oceanography 40 (2010): 2381-2400 en_US
dc.identifier.uri http://hdl.handle.net/1912/4290
dc.description Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 2381-2400, doi:10.1175/2010JPO4403.1. en_US
dc.description.abstract Langmuir circulation (LC) is a turbulent upper-ocean process driven by wind and surface waves that contributes significantly to the transport of momentum, heat, and mass in the oceanic surface layer. The authors have previously performed a direct comparison of large-eddy simulations and observations of the upper-ocean response to a wind event with rapid mixed layer deepening. The evolution of simulated crosswind velocity variance and spatial scales, as well as mixed layer deepening, was only consistent with observations if LC effects are included in the model. Based on an analysis of these validated simulations, in this study the fundamental differences in mixing between purely shear-driven turbulence and turbulence with LC are identified. In the former case, turbulent kinetic energy (TKE) production due to shear instabilities is largest near the surface, gradually decreasing to zero near the base of the mixed layer. This stands in contrast to the LC case in which at middepth range TKE production can be dominated by Stokes drift shear. Furthermore, the Eulerian mean vertical shear peaks near the base of the mixed layer so that TKE production by mean shear flow is elevated there. LC transports horizontal momentum efficiently downward leading to an along-wind velocity jet below LC downwelling regions at the base of the mixed layer. Locally enhanced vertical shear instabilities as a result of this jet efficiently erode the thermocline. In turn, enhanced breaking internal waves inject cold deep water into the mixed layer, where LC currents transport temperature perturbation advectively. Thus, LC and locally generated shear instabilities work intimately together to facilitate strongly the mixed layer deepening process. en_US
dc.description.sponsorship This research was supported by the Office of Naval Research through Grants N00014-09-M-0112 (TK) and N00014-06-1-0178 (AP, JT). Author TK also received support from a Woods Hole Oceanographic Institution Cooperative Institute for Climate and Ocean Research Postdoctoral Scholarship. en_US
dc.format.mimetype application/pdf
dc.language.iso en_US en_US
dc.publisher American Meteorological Society en_US
dc.relation.uri http://dx.doi.org/10.1175/2010JPO4403.1
dc.subject Mixed layer en_US
dc.subject Shear structure/flows en_US
dc.subject Wind effects en_US
dc.subject Turbulence en_US
dc.subject Thermocline en_US
dc.subject Internal waves en_US
dc.subject Advection en_US
dc.title Rapid mixed layer depening by the combination of Langmuir and shear instabilities : a case study en_US
dc.type Article en_US
dc.identifier.doi 10.1175/2010JPO4403.1


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