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

Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment
Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment
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.
Southern Ocean, Atmosphere-ocean interaction, Diapycnal mixing, Shear structure/flows, Oceanic mixed layer, Kelvin-Helmholtz instabilities
0022-3670
1798-1810
Brannigan, Liam
6093fdb8-8cae-42ee-8a10-9ee87288fed3
Lenn, Yueng-Djern
083a4d58-6bfc-4465-bb58-c2493e873d0a
Rippeth, Tom P.
249bf4a1-2416-4d49-b7a2-e1e2e1196219
McDonagh, Elaine
47e26eeb-b774-4068-af07-31847e42b977
Chereskin, Teresa K.
6c297d0b-f5e3-4d38-b308-a5f7023770b9
Sprintall, Janet
b7debd02-ea8a-44c9-b097-c5ac231a1bb2
Brannigan, Liam
6093fdb8-8cae-42ee-8a10-9ee87288fed3
Lenn, Yueng-Djern
083a4d58-6bfc-4465-bb58-c2493e873d0a
Rippeth, Tom P.
249bf4a1-2416-4d49-b7a2-e1e2e1196219
McDonagh, Elaine
47e26eeb-b774-4068-af07-31847e42b977
Chereskin, Teresa K.
6c297d0b-f5e3-4d38-b308-a5f7023770b9
Sprintall, Janet
b7debd02-ea8a-44c9-b097-c5ac231a1bb2

Brannigan, Liam, Lenn, Yueng-Djern, Rippeth, Tom P., McDonagh, Elaine, Chereskin, Teresa K. and Sprintall, Janet (2013) Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment. Journal of Physical Oceanography, 43 (8), 1798-1810. (doi:10.1175/JPO-D-12-0104.1).

Record type: Article

Abstract

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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More information

Published date: August 2013
Keywords: Southern Ocean, Atmosphere-ocean interaction, Diapycnal mixing, Shear structure/flows, Oceanic mixed layer, Kelvin-Helmholtz instabilities
Organisations: Marine Physics and Ocean Climate

Identifiers

Local EPrints ID: 356885
URI: https://eprints.soton.ac.uk/id/eprint/356885
ISSN: 0022-3670
PURE UUID: e8f684e3-0b46-4bd0-8761-7bea68dda429

Catalogue record

Date deposited: 16 Sep 2013 14:18
Last modified: 16 Jul 2019 21:23

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Contributors

Author: Liam Brannigan
Author: Yueng-Djern Lenn
Author: Tom P. Rippeth
Author: Elaine McDonagh
Author: Teresa K. Chereskin
Author: Janet Sprintall

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