Planetary-geometric constraints on isopycnal slope in the Southern Ocean
On planetary scales, surface wind stress and differential buoyancy forcing act together to produce isopycnal surfaces that are relatively flat in the tropics/subtropics and steep near the poles, where they tend to outcrop. Tilted isopycnals in a rapidly rotating fluid are subject to baroclinic insta...
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ftnerc:oai:nora.nerc.ac.uk:509723 2023-05-15T18:25:12+02:00 Planetary-geometric constraints on isopycnal slope in the Southern Ocean Jones, Daniel C. Ito, Takamitsu Birner, Thomas Klocker, Andreas Munday, David 2015-12 text http://nora.nerc.ac.uk/id/eprint/509723/ https://nora.nerc.ac.uk/id/eprint/509723/1/jpo-d-15-0034%252E1.pdf en eng American Meteorological Society https://nora.nerc.ac.uk/id/eprint/509723/1/jpo-d-15-0034%252E1.pdf Jones, Daniel C. orcid:0000-0002-8701-4506 Ito, Takamitsu; Birner, Thomas; Klocker, Andreas; Munday, David orcid:0000-0003-1920-708X . 2015 Planetary-geometric constraints on isopycnal slope in the Southern Ocean. Journal of Physical Oceanography, 45 (12). 2991-3004. https://doi.org/10.1175/JPO-D-15-0034.1 <https://doi.org/10.1175/JPO-D-15-0034.1> Publication - Article PeerReviewed 2015 ftnerc https://doi.org/10.1175/JPO-D-15-0034.1 2023-02-04T19:41:01Z On planetary scales, surface wind stress and differential buoyancy forcing act together to produce isopycnal surfaces that are relatively flat in the tropics/subtropics and steep near the poles, where they tend to outcrop. Tilted isopycnals in a rapidly rotating fluid are subject to baroclinic instability. The turbulent, mesoscale eddies generated by this instability have a tendency to homogenize potential vorticity (PV) along density surfaces. In the Southern Ocean (SO), the tilt of isopycnals is largely maintained by competition between the steepening effect of surface forcing and the flattening effect of turbulent, spatially inhomogeneous eddy fluxes of PV. Here we use quasi-geostrophic theory to investigate the influence of a planetary-geometric constraint on the equilibrium slope of tilted density/buoyancy surfaces in the SO. If the meridional gradients of relative vorticity and PV are small relative to β, then quasi-geostrophic theory predicts ds/dz = β/ f0 = cot(ϕ0)/a, or equivalently r ≡ |∂zs/(β/ f0)| = 1, where s is the isopycnal slope, ϕ0 is a reference latitude, a is the planetary radius, and r is the depth-averaged criticality parameter. We find that the strict r = 1 condition holds over specific averaging volumes in a large-scale climatology. A weaker r = O(1) condition for depth-averaged quantities is generally satisfied away from large bathymetric features. We employ the r = O(1) constraint to derive a depth scale to characterize large-scale interior stratification, and we use an idealized sector model to test the sensitivity of this relationship to surface wind forcing. Finally, we discuss the possible implications for eddy flux parameterization and for the sensitivity of SO circulation/stratification to changes in forcing. Article in Journal/Newspaper Southern Ocean Natural Environment Research Council: NERC Open Research Archive Southern Ocean Journal of Physical Oceanography 45 12 2991 3004 |
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Open Polar |
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Natural Environment Research Council: NERC Open Research Archive |
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English |
description |
On planetary scales, surface wind stress and differential buoyancy forcing act together to produce isopycnal surfaces that are relatively flat in the tropics/subtropics and steep near the poles, where they tend to outcrop. Tilted isopycnals in a rapidly rotating fluid are subject to baroclinic instability. The turbulent, mesoscale eddies generated by this instability have a tendency to homogenize potential vorticity (PV) along density surfaces. In the Southern Ocean (SO), the tilt of isopycnals is largely maintained by competition between the steepening effect of surface forcing and the flattening effect of turbulent, spatially inhomogeneous eddy fluxes of PV. Here we use quasi-geostrophic theory to investigate the influence of a planetary-geometric constraint on the equilibrium slope of tilted density/buoyancy surfaces in the SO. If the meridional gradients of relative vorticity and PV are small relative to β, then quasi-geostrophic theory predicts ds/dz = β/ f0 = cot(ϕ0)/a, or equivalently r ≡ |∂zs/(β/ f0)| = 1, where s is the isopycnal slope, ϕ0 is a reference latitude, a is the planetary radius, and r is the depth-averaged criticality parameter. We find that the strict r = 1 condition holds over specific averaging volumes in a large-scale climatology. A weaker r = O(1) condition for depth-averaged quantities is generally satisfied away from large bathymetric features. We employ the r = O(1) constraint to derive a depth scale to characterize large-scale interior stratification, and we use an idealized sector model to test the sensitivity of this relationship to surface wind forcing. Finally, we discuss the possible implications for eddy flux parameterization and for the sensitivity of SO circulation/stratification to changes in forcing. |
format |
Article in Journal/Newspaper |
author |
Jones, Daniel C. Ito, Takamitsu Birner, Thomas Klocker, Andreas Munday, David |
spellingShingle |
Jones, Daniel C. Ito, Takamitsu Birner, Thomas Klocker, Andreas Munday, David Planetary-geometric constraints on isopycnal slope in the Southern Ocean |
author_facet |
Jones, Daniel C. Ito, Takamitsu Birner, Thomas Klocker, Andreas Munday, David |
author_sort |
Jones, Daniel C. |
title |
Planetary-geometric constraints on isopycnal slope in the Southern Ocean |
title_short |
Planetary-geometric constraints on isopycnal slope in the Southern Ocean |
title_full |
Planetary-geometric constraints on isopycnal slope in the Southern Ocean |
title_fullStr |
Planetary-geometric constraints on isopycnal slope in the Southern Ocean |
title_full_unstemmed |
Planetary-geometric constraints on isopycnal slope in the Southern Ocean |
title_sort |
planetary-geometric constraints on isopycnal slope in the southern ocean |
publisher |
American Meteorological Society |
publishDate |
2015 |
url |
http://nora.nerc.ac.uk/id/eprint/509723/ https://nora.nerc.ac.uk/id/eprint/509723/1/jpo-d-15-0034%252E1.pdf |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_relation |
https://nora.nerc.ac.uk/id/eprint/509723/1/jpo-d-15-0034%252E1.pdf Jones, Daniel C. orcid:0000-0002-8701-4506 Ito, Takamitsu; Birner, Thomas; Klocker, Andreas; Munday, David orcid:0000-0003-1920-708X . 2015 Planetary-geometric constraints on isopycnal slope in the Southern Ocean. Journal of Physical Oceanography, 45 (12). 2991-3004. https://doi.org/10.1175/JPO-D-15-0034.1 <https://doi.org/10.1175/JPO-D-15-0034.1> |
op_doi |
https://doi.org/10.1175/JPO-D-15-0034.1 |
container_title |
Journal of Physical Oceanography |
container_volume |
45 |
container_issue |
12 |
container_start_page |
2991 |
op_container_end_page |
3004 |
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1766206474625744896 |