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Observed eddy-internal wave interactions in the Southern Ocean

Observed eddy-internal wave interactions in the Southern Ocean
Observed eddy-internal wave interactions in the Southern Ocean
The physical mechanisms that remove energy from the Southern Ocean’s vigorous mesoscale eddy field are not well understood. One proposed mechanism is direct energy transfer to the internal wave field in the ocean interior, via eddy-induced straining and shearing of preexisting internal waves. The magnitude, vertical structure, and temporal variability of the rate of energy transfer between eddies and internal waves is quantified from a 14-month deployment of a mooring cluster in the Scotia Sea. Velocity and buoyancy observations are decomposed into wave and eddy components, and the energy transfer is estimated using the Reynolds-averaged energy equation. We find that eddies gain energy from the internal wave field at a rate of −2.2 ± 0.6 mW m−2, integrated from the bottom to 566 m below the surface. This result can be decomposed into a positive (eddy to wave) component, equal to 0.2 ± 0.1 mW m−2, driven by horizontal straining of internal waves, and a negative (wave to eddy) component, equal to −2.5 ± 0.6 mW m−2, driven by vertical shearing of the wave spectrum. Temporal variability of the transfer rate is much greater than the mean value. Close to topography, large energy transfers are associated with low-frequency buoyancy fluxes, the underpinning physics of which do not conform to linear wave dynamics and are thereby in need of further research. Our work suggests that eddy–internal wave interactions may play a significant role in the energy balance of the Southern Ocean mesoscale eddy and internal wave fields.
0022-3670
3043-3062
Cusack, Jesse M.
637e34b0-29b7-43be-8290-51648580db8b
Brearley, J. Alexander
74993854-269c-4802-9b30-b3c34da8206d
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Smeed, David A.
2f7e2df1-c899-4d7a-94ef-d47ddb1cc494
Polzin, Kurt L.
2424c950-d9b0-471c-95c0-b7b9d44132a1
Velzeboer, Nick
3b49ab96-6f95-4195-b777-dbc3e025b8e1
Shakespeare, Callum J.
891eb7fc-1465-4536-86a9-8cd8fb6a49aa
Cusack, Jesse M.
637e34b0-29b7-43be-8290-51648580db8b
Brearley, J. Alexander
74993854-269c-4802-9b30-b3c34da8206d
Naveira Garabato, Alberto C.
97c0e923-f076-4b38-b89b-938e11cea7a6
Smeed, David A.
2f7e2df1-c899-4d7a-94ef-d47ddb1cc494
Polzin, Kurt L.
2424c950-d9b0-471c-95c0-b7b9d44132a1
Velzeboer, Nick
3b49ab96-6f95-4195-b777-dbc3e025b8e1
Shakespeare, Callum J.
891eb7fc-1465-4536-86a9-8cd8fb6a49aa

Cusack, Jesse M., Brearley, J. Alexander, Naveira Garabato, Alberto C., Smeed, David A., Polzin, Kurt L., Velzeboer, Nick and Shakespeare, Callum J. (2020) Observed eddy-internal wave interactions in the Southern Ocean. Journal of Physical Oceanography, 50 (10), 3043-3062. (doi:10.1175/JPO-D-20-0001.1).

Record type: Article

Abstract

The physical mechanisms that remove energy from the Southern Ocean’s vigorous mesoscale eddy field are not well understood. One proposed mechanism is direct energy transfer to the internal wave field in the ocean interior, via eddy-induced straining and shearing of preexisting internal waves. The magnitude, vertical structure, and temporal variability of the rate of energy transfer between eddies and internal waves is quantified from a 14-month deployment of a mooring cluster in the Scotia Sea. Velocity and buoyancy observations are decomposed into wave and eddy components, and the energy transfer is estimated using the Reynolds-averaged energy equation. We find that eddies gain energy from the internal wave field at a rate of −2.2 ± 0.6 mW m−2, integrated from the bottom to 566 m below the surface. This result can be decomposed into a positive (eddy to wave) component, equal to 0.2 ± 0.1 mW m−2, driven by horizontal straining of internal waves, and a negative (wave to eddy) component, equal to −2.5 ± 0.6 mW m−2, driven by vertical shearing of the wave spectrum. Temporal variability of the transfer rate is much greater than the mean value. Close to topography, large energy transfers are associated with low-frequency buoyancy fluxes, the underpinning physics of which do not conform to linear wave dynamics and are thereby in need of further research. Our work suggests that eddy–internal wave interactions may play a significant role in the energy balance of the Southern Ocean mesoscale eddy and internal wave fields.

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Accepted/In Press date: 3 July 2020
Published date: 15 October 2020

Identifiers

Local EPrints ID: 445030
URI: http://eprints.soton.ac.uk/id/eprint/445030
ISSN: 0022-3670
PURE UUID: b2c5be32-eff3-4b02-b794-f344f2aae0b8
ORCID for Jesse M. Cusack: ORCID iD orcid.org/0000-0003-2065-4397

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Date deposited: 18 Nov 2020 17:30
Last modified: 25 Nov 2021 17:45

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Contributors

Author: Jesse M. Cusack ORCID iD
Author: J. Alexander Brearley
Author: David A. Smeed
Author: Kurt L. Polzin
Author: Nick Velzeboer
Author: Callum J. Shakespeare

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