Why Are There Agulhas Rings?

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dc.contributor.authorPichevin, Thierry
dc.contributor.authorNof, Doron
dc.contributor.authorLutjeharms, Johann
dc.date.accessioned2021-10-08T07:08:15Z
dc.date.available2021-10-08T07:08:15Z
dc.date.issued1999
dc.description.abstractThe recently proposed analytical theory of Nof and Pichevin describing the intimate relationship between retroflecting currents and the production of rings is examined numerically and applied to the Agulhas Current. Using a reduced-gravity 11/2-layer primitive equation model of the Bleck and Boudra type the authors show that, as the theory suggests, the generation of rings from a retroflecting current is inevitable. The generation of rings is not due to an instability associated with the breakdown of a known steady solution but rather is due to the zonal momentum flux (i.e., flow force) of the Agulhas jet that curves back on itself. Numerical experiments demonstrate that, to compensate for this flow force, several rings are produced each year. Since the slowly drifting rings need to balance the entire flow force of the retroflecting jet, their length scale is considerably larger than the Rossby radius; that is, their scale is greater than that of their classical counterparts produced by instability. Recent observations suggest a correlation between the so-called Natal Pulse and the production of Agulhas rings. As a by-product of the more general retroflection experiments, the pulse issue is also examined numerically using two different representations for the pulses. The first is a meander pulse (i.e., the pulse is similar to a meander) and the second is a transport pulse. It is shown that, in this model, there is no obvious relationship between the presence of Natal pulses and the production of rings.
dc.identifier.apacitationPichevin, T., Nof, D., & Lutjeharms, J. (1999). Why Are There Agulhas Rings?. <i>Journal of Physical Oceanography</i>, 29(4), 693 - 707. http://hdl.handle.net/11427/34533en_ZA
dc.identifier.chicagocitationPichevin, Thierry, Doron Nof, and Johann Lutjeharms "Why Are There Agulhas Rings?." <i>Journal of Physical Oceanography</i> 29, 4. (1999): 693 - 707. http://hdl.handle.net/11427/34533en_ZA
dc.identifier.citationPichevin, T., Nof, D. & Lutjeharms, J. 1999. Why Are There Agulhas Rings?. <i>Journal of Physical Oceanography.</i> 29(4):693 - 707. http://hdl.handle.net/11427/34533en_ZA
dc.identifier.issn0022-3670
dc.identifier.issn1520-0485
dc.identifier.ris TY - Journal Article AU - Pichevin, Thierry AU - Nof, Doron AU - Lutjeharms, Johann AB - The recently proposed analytical theory of Nof and Pichevin describing the intimate relationship between retroflecting currents and the production of rings is examined numerically and applied to the Agulhas Current. Using a reduced-gravity 11/2-layer primitive equation model of the Bleck and Boudra type the authors show that, as the theory suggests, the generation of rings from a retroflecting current is inevitable. The generation of rings is not due to an instability associated with the breakdown of a known steady solution but rather is due to the zonal momentum flux (i.e., flow force) of the Agulhas jet that curves back on itself. Numerical experiments demonstrate that, to compensate for this flow force, several rings are produced each year. Since the slowly drifting rings need to balance the entire flow force of the retroflecting jet, their length scale is considerably larger than the Rossby radius; that is, their scale is greater than that of their classical counterparts produced by instability. Recent observations suggest a correlation between the so-called Natal Pulse and the production of Agulhas rings. As a by-product of the more general retroflection experiments, the pulse issue is also examined numerically using two different representations for the pulses. The first is a meander pulse (i.e., the pulse is similar to a meander) and the second is a transport pulse. It is shown that, in this model, there is no obvious relationship between the presence of Natal pulses and the production of rings. DA - 1999 DB - OpenUCT DP - University of Cape Town IS - 4 J1 - Journal of Physical Oceanography LK - https://open.uct.ac.za PY - 1999 SM - 0022-3670 SM - 1520-0485 T1 - Why Are There Agulhas Rings? TI - Why Are There Agulhas Rings? UR - http://hdl.handle.net/11427/34533 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34533
dc.identifier.vancouvercitationPichevin T, Nof D, Lutjeharms J. Why Are There Agulhas Rings?. Journal of Physical Oceanography. 1999;29(4):693 - 707. http://hdl.handle.net/11427/34533.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Oceanography
dc.publisher.facultyFaculty of Science
dc.sourceJournal of Physical Oceanography
dc.source.journalissue4
dc.source.journalvolume29
dc.source.pagination693 - 707
dc.source.urihttps://dx.doi.org/10.1175/1520-0485(1999)029<0693:WATAR>2.0.CO;2
dc.subject.otherSea current
dc.subject.otherRing current
dc.subject.otherNumerical method
dc.subject.otherJet(atmosphere, ocean)
dc.subject.otherWestern boundary current
dc.subject.otherExperimental study
dc.subject.otherSensitivity analysis
dc.subject.otherAgulhas current
dc.subject.otherCourant marin
dc.subject.otherCourant annulaire
dc.subject.otherMéthode numérique
dc.subject.otherJet(atmosphère, océan)
dc.subject.otherVeine limite occidentale
dc.subject.otherEtude expérimentale
dc.subject.otherAnalyse sensibilité
dc.subject.otherCourant Agulhas
dc.subject.otherCorriente marina
dc.subject.otherCorriente anular
dc.subject.otherMétodo numérico
dc.subject.otherChorro(atmósfera, océano)
dc.titleWhy Are There Agulhas Rings?
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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