Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere
The baroclinically unstable wind- and buoyancy-driven flow in a zonally reentrant pie-shaped sector on a sphere is numerically modeled and then analyzed using the transformed Eulerian-mean (TEM) formalism. Mean fields are obtained by zonal and time averaging performed at fixed height. The very large...
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| Format: | Article |
| Language: | en_US |
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American Meteorological Society
2010
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| Online Access: | http://hdl.handle.net/1721.1/51813 https://orcid.org/0000-0002-6716-1576 |
| _version_ | 1826196155275411456 |
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| author | Cerovecki, Ivana Plumb, R. Alan Heres, William |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Cerovecki, Ivana Plumb, R. Alan Heres, William |
| author_sort | Cerovecki, Ivana |
| collection | MIT |
| description | The baroclinically unstable wind- and buoyancy-driven flow in a zonally reentrant pie-shaped sector on a sphere is numerically modeled and then analyzed using the transformed Eulerian-mean (TEM) formalism. Mean fields are obtained by zonal and time averaging performed at fixed height. The very large latitudinal extent of the basin (50.7°S latitude to the equator) allows the latitude variation of the Coriolis parameter to strongly influence the flow. Persistent zonal jets are observed in the statistically steady state. Reynolds stress terms play an important role in redistributing zonal angular momentum: convergence of the lateral momentum flux gives rise to a strong eastward jet, with an adjacent westward jet equatorward and weaker multiple jets poleward. An equally prominent feature of the flow is a strong and persistent eddy that has the structure of a Kelvin cat’s eye and generally occupies the zonal width of the basin at latitudes 15°–10°S.
A strongly mixed surface diabatic zone overlies the near-adiabatic interior, within which Ertel potential vorticity (but not thickness) is homogenized along the mean isopycnals everywhere in the basin where eddies have developed (and thus is not homogenized equatorward of the most energetic eastward jet). A region of low potential vorticity (PV) is formed adjacent to the strong baroclinic front associated with that jet and subsequently maintained by strong convective events.
The eddy buoyancy flux is dominated by its skew component over large parts of the near-adiabatic interior, with cross-isopycnal components present only in the vicinity of the main jet and in the surface diabatic layer. Close to the main jet, the cross-isopycnal components are dominantly balanced by the triple correlation terms in the buoyancy variance budget, while the advection of buoyancy variance by the mean flow is not a dominant term in the eddy buoyancy variance budget.
Along-isopycnal mixing in the near-adiabatic interior is estimated by applying the effective diffusivity diagnostic of Nakamura. The effective diffusivity is large at the flanks of the mean jet and beneath it and small in the jet core. The apparent horizontal diffusivity for buoyancy obtained from the flux–gradient relationship is the same magnitude as the effective diffusivity, but the structures are rather different. The diapycnal diffusivity is strongest in the surface layer and also in a convectively unstable region that extends to depths of hundreds of meters beneath the equatorward flank of the main jet. |
| first_indexed | 2024-09-23T10:21:59Z |
| format | Article |
| id | mit-1721.1/51813 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T10:21:59Z |
| publishDate | 2010 |
| publisher | American Meteorological Society |
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| spelling | mit-1721.1/518132022-09-26T17:25:31Z Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere Cerovecki, Ivana Plumb, R. Alan Heres, William Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Plumb, R. Alan Cerovecki, Ivana Plumb, R. Alan The baroclinically unstable wind- and buoyancy-driven flow in a zonally reentrant pie-shaped sector on a sphere is numerically modeled and then analyzed using the transformed Eulerian-mean (TEM) formalism. Mean fields are obtained by zonal and time averaging performed at fixed height. The very large latitudinal extent of the basin (50.7°S latitude to the equator) allows the latitude variation of the Coriolis parameter to strongly influence the flow. Persistent zonal jets are observed in the statistically steady state. Reynolds stress terms play an important role in redistributing zonal angular momentum: convergence of the lateral momentum flux gives rise to a strong eastward jet, with an adjacent westward jet equatorward and weaker multiple jets poleward. An equally prominent feature of the flow is a strong and persistent eddy that has the structure of a Kelvin cat’s eye and generally occupies the zonal width of the basin at latitudes 15°–10°S. A strongly mixed surface diabatic zone overlies the near-adiabatic interior, within which Ertel potential vorticity (but not thickness) is homogenized along the mean isopycnals everywhere in the basin where eddies have developed (and thus is not homogenized equatorward of the most energetic eastward jet). A region of low potential vorticity (PV) is formed adjacent to the strong baroclinic front associated with that jet and subsequently maintained by strong convective events. The eddy buoyancy flux is dominated by its skew component over large parts of the near-adiabatic interior, with cross-isopycnal components present only in the vicinity of the main jet and in the surface diabatic layer. Close to the main jet, the cross-isopycnal components are dominantly balanced by the triple correlation terms in the buoyancy variance budget, while the advection of buoyancy variance by the mean flow is not a dominant term in the eddy buoyancy variance budget. Along-isopycnal mixing in the near-adiabatic interior is estimated by applying the effective diffusivity diagnostic of Nakamura. The effective diffusivity is large at the flanks of the mean jet and beneath it and small in the jet core. The apparent horizontal diffusivity for buoyancy obtained from the flux–gradient relationship is the same magnitude as the effective diffusivity, but the structures are rather different. The diapycnal diffusivity is strongest in the surface layer and also in a convectively unstable region that extends to depths of hundreds of meters beneath the equatorward flank of the main jet. National Science Foundation 2010-02-24T18:15:26Z 2010-02-24T18:15:26Z 2009-05 2008-10 Article http://purl.org/eprint/type/JournalArticle 0022-3670 http://hdl.handle.net/1721.1/51813 Cerovečki, Ivana, R. Alan Plumb, and William Heres. “Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere.” Journal of Physical Oceanography 39.5 (2009): 1133-1149 . ©2009 American Meteorological Society. https://orcid.org/0000-0002-6716-1576 en_US http://dx.doi.org/10.1175/2008jpo3596.1 Journal of Physical Oceanography Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Meteorological Society AMS |
| spellingShingle | Cerovecki, Ivana Plumb, R. Alan Heres, William Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere |
| title | Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere |
| title_full | Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere |
| title_fullStr | Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere |
| title_full_unstemmed | Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere |
| title_short | Eddy Transport and Mixing in a Wind- and Buoyancy-Driven Jet on the Sphere |
| title_sort | eddy transport and mixing in a wind and buoyancy driven jet on the sphere |
| url | http://hdl.handle.net/1721.1/51813 https://orcid.org/0000-0002-6716-1576 |
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