Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean
Downstream of Drake Passage, the Antarctic Circumpolar Current (ACC) veers abruptly northward along the continental slope of South America. This spins down the ACC, akin to the western boundary currents of ocean gyres. During this northward excursion, the mean potential vorticity (PV) increases dram...
Published in: | Journal of Physical Oceanography |
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Language: | English |
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American Meteorological Society
2022
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Online Access: | https://doi.org/10.1175/jpo-d-21-0195.1 https://ora.ox.ac.uk/objects/uuid:16ef3e9b-7aa6-4139-9359-bb52d6fd7ca8 |
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ftuloxford:oai:ora.ox.ac.uk:uuid:16ef3e9b-7aa6-4139-9359-bb52d6fd7ca8 2023-05-15T13:56:55+02:00 Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean Stanley, GJ Marshall, DP 2022-04-13 https://doi.org/10.1175/jpo-d-21-0195.1 https://ora.ox.ac.uk/objects/uuid:16ef3e9b-7aa6-4139-9359-bb52d6fd7ca8 eng eng American Meteorological Society doi:10.1175/jpo-d-21-0195.1 https://ora.ox.ac.uk/objects/uuid:16ef3e9b-7aa6-4139-9359-bb52d6fd7ca8 https://doi.org/10.1175/jpo-d-21-0195.1 info:eu-repo/semantics/openAccess CC Attribution (CC BY) CC-BY Journal article 2022 ftuloxford https://doi.org/10.1175/jpo-d-21-0195.1 2022-10-13T22:06:11Z Downstream of Drake Passage, the Antarctic Circumpolar Current (ACC) veers abruptly northward along the continental slope of South America. This spins down the ACC, akin to the western boundary currents of ocean gyres. During this northward excursion, the mean potential vorticity (PV) increases dramatically (decreases in magnitude) by up to a factor of two along mean geostrophic streamlines on mid-depth buoyancy surfaces. This increase is driven by drag near the continental slope, or by breaking eddies further offshore, and is balanced by a remarkably steady, eddy-driven decrease of mean PV along these northern circumpolar streamlines in the open ocean. We show how two related eddy processes that are fundamental to ACC dynamics — poleward buoyancy fluxes and downward fluxes of eastward momentum — are also concomitant with materially forcing PV to increase on the northern flank of a jet at mid-depth, and decrease on the southern flank. For eddies to drive the required mean PV decrease along northern streamlines, the ACC merges with the subtropical gyres to the north, so these streamlines inhabit the southern flanks of the combined ACC-gyre jets. We support these ideas by analyzing the time-mean PV and its budget along time-mean geostrophic streamlines in the Southern Ocean State Estimate. Our averaging formalism is Eulerian, to match the model’s numerics. The Thickness Weighted Average is preferable, but its PV budget cannot be balanced using Eulerian 5-day averaged diagnostics, primarily because the z-level buoyancy and continuity equations’ delicate balances are destroyed upon transformation into the buoyancy-coordinate thickness equation. Article in Journal/Newspaper Antarc* Antarctic Drake Passage Southern Ocean ORA - Oxford University Research Archive Antarctic Drake Passage Southern Ocean The Antarctic Journal of Physical Oceanography |
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Open Polar |
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ORA - Oxford University Research Archive |
op_collection_id |
ftuloxford |
language |
English |
description |
Downstream of Drake Passage, the Antarctic Circumpolar Current (ACC) veers abruptly northward along the continental slope of South America. This spins down the ACC, akin to the western boundary currents of ocean gyres. During this northward excursion, the mean potential vorticity (PV) increases dramatically (decreases in magnitude) by up to a factor of two along mean geostrophic streamlines on mid-depth buoyancy surfaces. This increase is driven by drag near the continental slope, or by breaking eddies further offshore, and is balanced by a remarkably steady, eddy-driven decrease of mean PV along these northern circumpolar streamlines in the open ocean. We show how two related eddy processes that are fundamental to ACC dynamics — poleward buoyancy fluxes and downward fluxes of eastward momentum — are also concomitant with materially forcing PV to increase on the northern flank of a jet at mid-depth, and decrease on the southern flank. For eddies to drive the required mean PV decrease along northern streamlines, the ACC merges with the subtropical gyres to the north, so these streamlines inhabit the southern flanks of the combined ACC-gyre jets. We support these ideas by analyzing the time-mean PV and its budget along time-mean geostrophic streamlines in the Southern Ocean State Estimate. Our averaging formalism is Eulerian, to match the model’s numerics. The Thickness Weighted Average is preferable, but its PV budget cannot be balanced using Eulerian 5-day averaged diagnostics, primarily because the z-level buoyancy and continuity equations’ delicate balances are destroyed upon transformation into the buoyancy-coordinate thickness equation. |
format |
Article in Journal/Newspaper |
author |
Stanley, GJ Marshall, DP |
spellingShingle |
Stanley, GJ Marshall, DP Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean |
author_facet |
Stanley, GJ Marshall, DP |
author_sort |
Stanley, GJ |
title |
Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean |
title_short |
Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean |
title_full |
Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean |
title_fullStr |
Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean |
title_full_unstemmed |
Why mean potential vorticity cannot be materially conserved in the eddying Southern Ocean |
title_sort |
why mean potential vorticity cannot be materially conserved in the eddying southern ocean |
publisher |
American Meteorological Society |
publishDate |
2022 |
url |
https://doi.org/10.1175/jpo-d-21-0195.1 https://ora.ox.ac.uk/objects/uuid:16ef3e9b-7aa6-4139-9359-bb52d6fd7ca8 |
geographic |
Antarctic Drake Passage Southern Ocean The Antarctic |
geographic_facet |
Antarctic Drake Passage Southern Ocean The Antarctic |
genre |
Antarc* Antarctic Drake Passage Southern Ocean |
genre_facet |
Antarc* Antarctic Drake Passage Southern Ocean |
op_relation |
doi:10.1175/jpo-d-21-0195.1 https://ora.ox.ac.uk/objects/uuid:16ef3e9b-7aa6-4139-9359-bb52d6fd7ca8 https://doi.org/10.1175/jpo-d-21-0195.1 |
op_rights |
info:eu-repo/semantics/openAccess CC Attribution (CC BY) |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.1175/jpo-d-21-0195.1 |
container_title |
Journal of Physical Oceanography |
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1766264524070977536 |