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Shear at the base of the oceanic mixed layer generated by wind shear alignment

TitleShear at the base of the oceanic mixed layer generated by wind shear alignment
Publication TypeJournal Article
Year of Publication2013
AuthorsBrannigan L., Lenn Y.D, Rippeth T.P, McDonagh E., Chereskin TK, Sprintall J
JournalJournal of Physical Oceanography
Date Published2013/08
Type of ArticleArticle
ISBN Number0022-3670
Accession NumberWOS:000323135400016
KeywordsAtmosphere-ocean interaction; circulation; currents; Diapycnal mixing; drake passage; driven; fields; flows; flux; Kelvin-Helmholtz instabilities; Oceanic mixed layer; Shear; Southern Ocean; structure; transition layer; variability

Observations are used to evaluate a simple theoretical model for the generation of near-inertial shear spikes at the base of the open ocean mixed layer when the upper ocean displays a two-layer structure. The model predicts that large changes in shear squared can be produced by the alignment of the wind and shear vectors. A climatology of stratification and shear variance in Drake Passage is presented, which shows that these assumptions are most applicable to summer, fall, and spring but are not highly applicable to winter. Temperature, salinity, and velocity data from a high spatial resolution cruise in Drake Passage show that the model does not predict all large changes in shear variance; the model is most effective at predicting changes in shear squared when it arises owing to near-inertial wind-driven currents without requiring a rotating resonant wind stress. The model is also more effective where there is a uniform mixed layer above a strongly stratified transition layer. Rotary spectral and statistical analysis of an additional 242 Drake Passage transects from 1999 to 2011 confirmed the presence of this shear-spiking mechanism, particularly in summer, spring, and fall when stratification is stronger.

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