Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary
Mesoscale eddies are ubiquitous dynamical features that tend to propagate westward and disappear along ocean western boundaries. Using a multiscale observational study, we assess the extent to which eddies dissipate via a direct cascade of energy at a western boundary. We analyze data from a ship‐ba...
Published in: | Journal of Geophysical Research: Oceans |
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ftnerc:oai:nora.nerc.ac.uk:529023 2023-05-15T17:34:47+02:00 Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary Evans, Dafydd Frajka-Williams, Eleanor Naveira Garabato, Alberto C. Polzin, Kurt L. Forryan, Alexander 2020-11-01 text http://nora.nerc.ac.uk/id/eprint/529023/ https://nora.nerc.ac.uk/id/eprint/529023/1/2020JC016246%20%281%29.pdf https://doi.org/10.1029/2020JC016246 en eng https://nora.nerc.ac.uk/id/eprint/529023/1/2020JC016246%20%281%29.pdf Evans, Dafydd orcid:0000-0002-6328-4093 Frajka-Williams, Eleanor orcid:0000-0001-8773-7838 Naveira Garabato, Alberto C.; Polzin, Kurt L.; Forryan, Alexander. 2020 Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary. Journal of Geophysical Research: Oceans, 125 (11), e2020JC016246. https://doi.org/10.1029/2020JC016246 <https://doi.org/10.1029/2020JC016246> cc_by_4 CC-BY Publication - Article PeerReviewed 2020 ftnerc https://doi.org/10.1029/2020JC016246 2023-02-04T19:51:22Z Mesoscale eddies are ubiquitous dynamical features that tend to propagate westward and disappear along ocean western boundaries. Using a multiscale observational study, we assess the extent to which eddies dissipate via a direct cascade of energy at a western boundary. We analyze data from a ship‐based microstructure and velocity survey, and an 18‐month mooring deployment, to document the dissipation of energy in anticyclonic and cyclonic eddies impinging on the topographic slope east of the Bahamas, in the North Atlantic Ocean. These observations reveal high levels of turbulence where the steep and rough topographic slope modified the intensified northward flow associated with, in particular, anticyclonic eddies. Elevated dissipation was observed both near‐bottom and at mid depths (200–800 m). Near‐bottom turbulence occurred in the lee of a protruding escarpment, where elevated Froude numbers suggest hydraulic control. Energy was also radiated in the form of upward‐propagating internal waves. Elevated dissipation at mid depths occurred in regions of strong vertical shear, where the topographic slope modified the vertical structure of the northward eddy flow. Here, low Richardson numbers and a local change in the isopycnal gradient of potential vorticity (PV) suggest that the elevated dissipation was associated with horizontal shear instability. Elevated mid‐depth dissipation was also induced by topographic steering of the flow. This led to large anticyclonic vorticity and negative PV adjacent to the topographic slope, suggesting that centrifugal instability underpinned the local enhancement in dissipation. Our results provide a mechanistic benchmark for the realistic representation of eddy dissipation in ocean models. Article in Journal/Newspaper North Atlantic Natural Environment Research Council: NERC Open Research Archive Journal of Geophysical Research: Oceans 125 11 |
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Open Polar |
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Natural Environment Research Council: NERC Open Research Archive |
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ftnerc |
language |
English |
description |
Mesoscale eddies are ubiquitous dynamical features that tend to propagate westward and disappear along ocean western boundaries. Using a multiscale observational study, we assess the extent to which eddies dissipate via a direct cascade of energy at a western boundary. We analyze data from a ship‐based microstructure and velocity survey, and an 18‐month mooring deployment, to document the dissipation of energy in anticyclonic and cyclonic eddies impinging on the topographic slope east of the Bahamas, in the North Atlantic Ocean. These observations reveal high levels of turbulence where the steep and rough topographic slope modified the intensified northward flow associated with, in particular, anticyclonic eddies. Elevated dissipation was observed both near‐bottom and at mid depths (200–800 m). Near‐bottom turbulence occurred in the lee of a protruding escarpment, where elevated Froude numbers suggest hydraulic control. Energy was also radiated in the form of upward‐propagating internal waves. Elevated dissipation at mid depths occurred in regions of strong vertical shear, where the topographic slope modified the vertical structure of the northward eddy flow. Here, low Richardson numbers and a local change in the isopycnal gradient of potential vorticity (PV) suggest that the elevated dissipation was associated with horizontal shear instability. Elevated mid‐depth dissipation was also induced by topographic steering of the flow. This led to large anticyclonic vorticity and negative PV adjacent to the topographic slope, suggesting that centrifugal instability underpinned the local enhancement in dissipation. Our results provide a mechanistic benchmark for the realistic representation of eddy dissipation in ocean models. |
format |
Article in Journal/Newspaper |
author |
Evans, Dafydd Frajka-Williams, Eleanor Naveira Garabato, Alberto C. Polzin, Kurt L. Forryan, Alexander |
spellingShingle |
Evans, Dafydd Frajka-Williams, Eleanor Naveira Garabato, Alberto C. Polzin, Kurt L. Forryan, Alexander Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
author_facet |
Evans, Dafydd Frajka-Williams, Eleanor Naveira Garabato, Alberto C. Polzin, Kurt L. Forryan, Alexander |
author_sort |
Evans, Dafydd |
title |
Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
title_short |
Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
title_full |
Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
title_fullStr |
Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
title_full_unstemmed |
Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
title_sort |
mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary |
publishDate |
2020 |
url |
http://nora.nerc.ac.uk/id/eprint/529023/ https://nora.nerc.ac.uk/id/eprint/529023/1/2020JC016246%20%281%29.pdf https://doi.org/10.1029/2020JC016246 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_relation |
https://nora.nerc.ac.uk/id/eprint/529023/1/2020JC016246%20%281%29.pdf Evans, Dafydd orcid:0000-0002-6328-4093 Frajka-Williams, Eleanor orcid:0000-0001-8773-7838 Naveira Garabato, Alberto C.; Polzin, Kurt L.; Forryan, Alexander. 2020 Mesoscale eddy dissipation by a “zoo” of submesoscale processes at a western boundary. Journal of Geophysical Research: Oceans, 125 (11), e2020JC016246. https://doi.org/10.1029/2020JC016246 <https://doi.org/10.1029/2020JC016246> |
op_rights |
cc_by_4 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.1029/2020JC016246 |
container_title |
Journal of Geophysical Research: Oceans |
container_volume |
125 |
container_issue |
11 |
_version_ |
1766133725892968448 |