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Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment

Liam Brannigan, Yueng-Djern Lenn, Tom P. Rippeth, Elaine McDonagh, Teresa K. Chereskin, Janet Sprintall
2013 Journal of Physical Oceanography  
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
more » ... d 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.
doi:10.1175/jpo-d-12-0104.1 fatcat:6m4frbig7vbazg5lqjvvdp2rua