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Observation of a large lee wave in the Drake Passage

Observation of a large lee wave in the Drake Passage
Observation of a large lee wave in the Drake Passage
Lee waves are thought to play a prominent role in Southern Ocean dynamics, facilitating a transfer of energy from the jets of the Antarctic Circumpolar Current to microscale, turbulent motions important in water mass transformations. Two EM-APEX profiling floats deployed in the Drake Passage during the Diapycnal and Isopycnal Mixing Experiment (DIMES) independently measured a 120 ± 20-m vertical amplitude lee wave over the Shackleton Fracture Zone. A model for steady EM-APEX motion is developed to calculate absolute vertical water velocity, augmenting the horizontal velocity measurements made by the floats. The wave exhibits fluctuations in all three velocity components of over 15 cm s−1 and an intrinsic frequency close to the local buoyancy frequency. The wave is observed to transport energy and horizontal momentum vertically at respective peak rates of 1.3 ± 0.2 W m−2 and 8 ± 1 N m−2. The rate of turbulent kinetic energy dissipation is estimated using both Thorpe scales and a method that isolates high-frequency vertical kinetic energy and is found to be enhanced within the wave to values of order 10−7 W kg−1. The observed vertical flux of energy is significantly larger than expected from idealized numerical simulations and also larger than observed depth-integrated dissipation rates. These results provide the first unambiguous observation of a lee wave in the Southern Ocean with simultaneous measurements of its energetics and dynamics.
0022-3670
793-810
Cusack, Jesse M.
637e34b0-29b7-43be-8290-51648580db8b
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Smeed, David A.
79eece5a-c870-47f9-bba0-0a4ef0369490
Girton, James B.
83fb0c2f-484c-443b-afca-5342108a5638
Cusack, Jesse M.
637e34b0-29b7-43be-8290-51648580db8b
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Smeed, David A.
79eece5a-c870-47f9-bba0-0a4ef0369490
Girton, James B.
83fb0c2f-484c-443b-afca-5342108a5638

Cusack, Jesse M., Naveira Garabato, Alberto C. and Smeed, David A. et al. (2017) Observation of a large lee wave in the Drake Passage. Journal of Physical Oceanography, 47 (4), 793-810. (doi:10.1175/JPO-D-16-0153.1).

Record type: Article

Abstract

Lee waves are thought to play a prominent role in Southern Ocean dynamics, facilitating a transfer of energy from the jets of the Antarctic Circumpolar Current to microscale, turbulent motions important in water mass transformations. Two EM-APEX profiling floats deployed in the Drake Passage during the Diapycnal and Isopycnal Mixing Experiment (DIMES) independently measured a 120 ± 20-m vertical amplitude lee wave over the Shackleton Fracture Zone. A model for steady EM-APEX motion is developed to calculate absolute vertical water velocity, augmenting the horizontal velocity measurements made by the floats. The wave exhibits fluctuations in all three velocity components of over 15 cm s−1 and an intrinsic frequency close to the local buoyancy frequency. The wave is observed to transport energy and horizontal momentum vertically at respective peak rates of 1.3 ± 0.2 W m−2 and 8 ± 1 N m−2. The rate of turbulent kinetic energy dissipation is estimated using both Thorpe scales and a method that isolates high-frequency vertical kinetic energy and is found to be enhanced within the wave to values of order 10−7 W kg−1. The observed vertical flux of energy is significantly larger than expected from idealized numerical simulations and also larger than observed depth-integrated dissipation rates. These results provide the first unambiguous observation of a lee wave in the Southern Ocean with simultaneous measurements of its energetics and dynamics.

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More information

Accepted/In Press date: 31 January 2017
Published date: 1 April 2017
Organisations: Ocean and Earth Science, Physical Oceanography, National Oceanography Centre, Marine Physics and Ocean Climate

Identifiers

Local EPrints ID: 405536
URI: http://eprints.soton.ac.uk/id/eprint/405536
ISSN: 0022-3670
PURE UUID: d5d2f36f-977c-4ae0-ae66-6f4b3164fe9e
ORCID for Jesse M. Cusack: ORCID iD orcid.org/0000-0003-2065-4397

Catalogue record

Date deposited: 06 Feb 2017 10:28
Last modified: 27 Apr 2022 08:43

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Contributors

Author: Jesse M. Cusack ORCID iD
Author: David A. Smeed
Author: James B. Girton

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