Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory

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dc.contributor.authorTailleux, Rémi
dc.contributor.authorLazar, Alban
dc.contributor.authorReason, C J C
dc.date.accessioned2021-10-08T07:08:15Z
dc.date.available2021-10-08T07:08:15Z
dc.date.issued2005
dc.description.abstractSubducted temperature anomalies have been invoked as a possible way for midlatitudes to alter the climate variability of equatorial regions through the so-called thermocline bridge, both in the Pacific and Atlantic Oceans. To have a significant impact on the equatorial heat balance, however, temperature anomalies must reach the equatorial regions sufficiently undamped. In the oceans, the amplitude of propagating temperature (and salinity) anomalies can be altered both by diabatic (nonconservative) and adiabatic (conservative) effects. The importance of adiabatic alterations depends on whether the anomalies are controlled by wave dynamics or by passive advection associated with density compensation. Waves being relatively well understood, this paper seeks to understand the amplitude variations of density-compensated temperature and salinity anomalies caused by adiabatic effects, for which no general methodology is available. The main assumption is that these can be computed independent of amplitude variations caused by diabatic effects. Because density compensation requires the equality T'/S' = βs/α to hold along mean trajectories, the ratio T'/S' may potentially undergo large amplitude variations if the ratio βs/α does, where a and βsare the thermal expansion and haline contraction coefficients, respectively. In the oceans, the ratio βs/α may decrease by an order-1 factor between the extratropical and tropical latitudes, hut such large variations are in general associated with diapycnal rather than isopycnal motion and hence are likely to be superimposed in practice with diabatically induced variations. To understand the individual variations of T' and S' along the mean streamlines, two distinct theories are constructed that respectively use density/salinity and density/spiciness as prognostic variables. If the coupling between the prognostic variables is neglected, as is usually done, both theories predict at leading order that temperature (salinity) anomalies should be systematically and significantly attenuated (conserved or amplified), on average, when propagating from extratropical to tropical latitudes. Along particular trajectories following isopycnals, however, both attenuation and amplification appear to be locally possible. Assuming that the density/spiciness formulation is the most accurate, which is supported by a theoretical assessment of higher-order effects, the present results provide an amplification mechanism for subducted salinity anomalies propagating equalorward, by which the latter could potentially affect decadal equatorial climate variability through their slow modulation of the equatorial mixed layer, perhaps more easily than their attenuated temperature counterparts. This could be by affecting, for instance, barrier layers by which salinity is known to strongly affect local heat fluxes and heat content.
dc.identifier.apacitationTailleux, R., Lazar, A., & Reason, C. J. C. (2005). Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory. <i>Journal of Physical Oceanography</i>, 35(5), 849 - 864. http://hdl.handle.net/11427/34534en_ZA
dc.identifier.chicagocitationTailleux, Rémi, Alban Lazar, and C J C Reason "Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory." <i>Journal of Physical Oceanography</i> 35, 5. (2005): 849 - 864. http://hdl.handle.net/11427/34534en_ZA
dc.identifier.citationTailleux, R., Lazar, A. & Reason, C.J.C. 2005. Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory. <i>Journal of Physical Oceanography.</i> 35(5):849 - 864. http://hdl.handle.net/11427/34534en_ZA
dc.identifier.issn0022-3670
dc.identifier.issn1520-0485
dc.identifier.ris TY - Journal Article AU - Tailleux, Rémi AU - Lazar, Alban AU - Reason, C J C AB - Subducted temperature anomalies have been invoked as a possible way for midlatitudes to alter the climate variability of equatorial regions through the so-called thermocline bridge, both in the Pacific and Atlantic Oceans. To have a significant impact on the equatorial heat balance, however, temperature anomalies must reach the equatorial regions sufficiently undamped. In the oceans, the amplitude of propagating temperature (and salinity) anomalies can be altered both by diabatic (nonconservative) and adiabatic (conservative) effects. The importance of adiabatic alterations depends on whether the anomalies are controlled by wave dynamics or by passive advection associated with density compensation. Waves being relatively well understood, this paper seeks to understand the amplitude variations of density-compensated temperature and salinity anomalies caused by adiabatic effects, for which no general methodology is available. The main assumption is that these can be computed independent of amplitude variations caused by diabatic effects. Because density compensation requires the equality T'/S' = βs/α to hold along mean trajectories, the ratio T'/S' may potentially undergo large amplitude variations if the ratio βs/α does, where a and βsare the thermal expansion and haline contraction coefficients, respectively. In the oceans, the ratio βs/α may decrease by an order-1 factor between the extratropical and tropical latitudes, hut such large variations are in general associated with diapycnal rather than isopycnal motion and hence are likely to be superimposed in practice with diabatically induced variations. To understand the individual variations of T' and S' along the mean streamlines, two distinct theories are constructed that respectively use density/salinity and density/spiciness as prognostic variables. If the coupling between the prognostic variables is neglected, as is usually done, both theories predict at leading order that temperature (salinity) anomalies should be systematically and significantly attenuated (conserved or amplified), on average, when propagating from extratropical to tropical latitudes. Along particular trajectories following isopycnals, however, both attenuation and amplification appear to be locally possible. Assuming that the density/spiciness formulation is the most accurate, which is supported by a theoretical assessment of higher-order effects, the present results provide an amplification mechanism for subducted salinity anomalies propagating equalorward, by which the latter could potentially affect decadal equatorial climate variability through their slow modulation of the equatorial mixed layer, perhaps more easily than their attenuated temperature counterparts. This could be by affecting, for instance, barrier layers by which salinity is known to strongly affect local heat fluxes and heat content. DA - 2005 DB - OpenUCT DP - University of Cape Town IS - 5 J1 - Journal of Physical Oceanography LK - https://open.uct.ac.za PY - 2005 SM - 0022-3670 SM - 1520-0485 T1 - Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory TI - Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory UR - http://hdl.handle.net/11427/34534 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34534
dc.identifier.vancouvercitationTailleux R, Lazar A, Reason CJC. Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory. Journal of Physical Oceanography. 2005;35(5):849 - 864. http://hdl.handle.net/11427/34534.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Oceanography
dc.publisher.facultyFaculty of Science
dc.sourceJournal of Physical Oceanography
dc.source.journalissue5
dc.source.journalvolume35
dc.source.pagination849 - 864
dc.source.urihttps://dx.doi.org/10.1175/JPO2706.1
dc.subject.othertheoretical studies
dc.subject.othercoupling
dc.subject.otherAmplification
dc.subject.otherattenuation
dc.subject.otherMeridional circulation
dc.subject.otherheat transfer
dc.subject.othersubduction
dc.subject.othersalinity
dc.subject.othertemperature
dc.subject.otheranomalies
dc.subject.otherocean-atmosphere interaction
dc.subject.otherEtude théorique
dc.subject.otherCouplage
dc.subject.otherAtténuation
dc.subject.otherCirculation méridienne
dc.subject.otherTransfert chaleur
dc.subject.otherSubduction
dc.subject.otherSalinité
dc.subject.otherTempérature
dc.subject.otherAnomalie
dc.subject.otherInteraction atmosphère océan
dc.subject.otherAmplificación
dc.titlePhysics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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