Transport driven by eddy momentum fluxes in the Gulf Stream Extension region

Greatbatch, Richard John; Zhai, Xiaoming; Claus, Martin; Czeschel, Lars; Rath, Willi

doi:10.1029/2010gl045473

Cited by 36 publications

(40 citation statements)

References 32 publications

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“…With the longer record of altimeter data that has now become available, a clearer and simpler picture emerges after zonal averaging (bold black line in Figure 6b): the eddies systematically extract westerly momentum from regions to the south and north of the Kuroshio Current and deposit it in the latitude band between 32°N and 35.5°N where the strongest zonalmean zonal flow is situated (see Figure 7 in Greatbatch et al (2010a)). We therefore conclude that, at least in the zonal-mean sense, eddy momentum fluxes in the Gulf Stream and Kuroshio Extensions are not that dissimilar: they both act to strengthen the western boundary current and drive the recirculation gyres to the north and south (Qiu et al, 2008;Greatbatch et al, 2010b).…”

Section: Eddy Momentum Fluxmentioning

confidence: 99%

“…It becomes clear that the eddies systematically extract westerly momentum from both sides of the Gulf Stream and flux it into the Gulf Stream jet in the latitude band between 37°N and 41°N. In doing so, the eddy momentum flux, u'ν', contributes to driving both the northern and southern recirculation gyres of the Gulf Stream (Greatbatch et al, 2010b).…”

Section: Eddy Momentum Fluxmentioning

confidence: 99%

“…Zhai et al, 2004;Hecht et al, 2008;Greatbatch et al, 2010b). The strength of the eddy activity, often measured by the energy carried by the eddies, varies on a variety of time scales ranging from seasonal to decadal (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The annual cycle of surface eddy kinetic energy and its influence on eddy momentum fluxes as inferred from altimeter data

Zhai

2017

som

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Abstract:The annual cycle of surface eddy kinetic energy (EKE) and its influence on eddy momentum fluxes are investigated using an updated record of satellite altimeter data. It is found that there is a phase difference between the annual cycles of EKE in the western boundary current regions and EKE in the interior of the subtropical gyres, suggesting that different mechanisms may be at work in different parts of the subtropical gyres. The annual cycles of EKE averaged in the two hemispheres are found to be of similar magnitude but in opposite phase. As a result, the globally-averaged EKE shows little seasonal variability. The longer record of altimeter data used in this study has brought out a clearer and simpler picture of eddy momentum fluxes in the Gulf Stream and Kuroshio Extensions: eddies in both regions systematically flux westerly momentum into the western boundary current jets. Considerable seasonal variations in eddy momentum fluxes are found in the western boundary current regions, which potentially play an important role in modulating the strength of the western boundary currents and their associated recirculation gyres on the seasonal time scale.

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Section: Eddy Momentum Fluxmentioning

confidence: 99%

Section: Eddy Momentum Fluxmentioning

confidence: 99%

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The annual cycle of surface eddy kinetic energy and its influence on eddy momentum fluxes as inferred from altimeter data

Zhai

2017

som

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“…This might indicate the effect of barotropic instability, for example at the western boundary of the Indian Ocean, and in the Kuroshio and the Gulf Stream regions. However, in the Gulf Stream extension region, the signal is clearly positive, indicating acceleration of the mean current by the eddies (Held and Andrews 1983;Greatbatch et al 2010;Waterman and Jayne 2011), in which the meridional radiation of Rossby waves could play a role (Thompson 1971).…”

Section: A Model Diagnosis In Density Coordinatesmentioning

confidence: 99%

Energetics of the Global Ocean: The Role of Mesoscale Eddies

Aiki

Zhai

Greatbatch

2015

World Scientific Series on Asia-Pacific Weather and Climate

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This article reviews the energy cycle of the global ocean circulation, focusing on the role of baroclinic mesoscale eddies. Two of the important effects of mesoscale eddies are: (i) the flattening of the slope of large-scale isopycnal surfaces by the eddy-induced overturning circulation, the basis for the Gent-McWilliams parametrization; and (ii) the vertical redistribution of the momentum of basic geostrophic currents by the eddy-induced form stress (the residual effect of pressure perturbations), the basis for the Greatbatch-Lamb parametrization. While only point (i) can be explained using the classical Lorenz energy diagram, both (i) and (ii) can be explained using the modified energy diagram of Bleck as in the following energy cycle. Wind forcing provides an input to the mean KE, which is then transferred to the available potential energy (APE) of the large-scale field by the wind-induced Ekman flow. Subsequently, the APE is extracted by the eddy-induced overturning circulation to feed the mean KE, indicating the enhancement of the vertical shear of the basic current. Meanwhile, the vertical shear of the basic current is relaxed by the eddy-induced form stress, taking the mean KE to endow the eddy field with an energy cascade. The above energy cycle is useful for understanding the dynamics of the Antarctic Circumpolar Current. On the other hand, while the source of the eddy field energy has become clearer, identifying the sink and flux of the eddy field energy in both physical and spectral space remains major challenges of present-day oceanography. A recent study using a combination of models, satellite altimetry, and climatological hydrographic data shows that the western boundary acts as a "graveyard" for the westward-propagating eddies.

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“…In energetic western boundary current extensions, mesoscale eddies are thought to play an important role in cross-jet transport of tracers such as heat (e.g., Wunsch 1999;Qiu and Chen 2005;Bishop et al 2013) and momentum (e.g., Hall 1991;Adamec 1998;Greatbatch et al 2010;Waterman et al 2011). Mesoscale eddy activity in the KE region is complex and takes a variety of forms.…”

Section: Introductionmentioning

confidence: 99%

Effects of Eddy Vorticity Forcing on the Mean State of the Kuroshio Extension

Delman

McClean

Sprintall

et al. 2015

Journal of Physical Oceanography

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Eddy-mean flow interactions along the Kuroshio Extension (KE) jet are investigated using a vorticity budget of a high-resolution ocean model simulation, averaged over a 13-yr period. The simulation explicitly resolves mesoscale eddies in the KE and is forced with air-sea fluxes representing the years 1995-2007. A mean-eddy decomposition in a jet-following coordinate system removes the variability of the jet path from the eddy components of velocity; thus, eddy kinetic energy in the jet reference frame is substantially lower than in geographic coordinates and exhibits a cross-jet asymmetry that is consistent with the baroclinic instability criterion of the long-term mean field. The vorticity budget is computed in both geographic (i.e., Eulerian) and jet reference frames; the jet frame budget reveals several patterns of eddy forcing that are largely attributed to varicose modes of variability. Eddies tend to diffuse the relative vorticity minima/maxima that flank the jet, removing momentum from the fast-moving jet core and reinforcing the quasi-permanent meridional meanders in the mean jet. A pattern associated with the vertical stretching of relative vorticity in eddies indicates a deceleration (acceleration) of the jet coincident with northward (southward) quasi-permanent meanders. Eddy relative vorticity advection outside of the eastward jet core is balanced mostly by vertical stretching of the mean flow, which through baroclinic adjustment helps to drive the flanking recirculation gyres. The jet frame vorticity budget presents a well-defined picture of eddy activity, illustrating along-jet variations in eddy-mean flow interaction that may have implications for the jet's dynamics and cross-frontal tracer fluxes.

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Transport driven by eddy momentum fluxes in the Gulf Stream Extension region

Cited by 36 publications

References 32 publications

The annual cycle of surface eddy kinetic energy and its influence on eddy momentum fluxes as inferred from altimeter data

The annual cycle of surface eddy kinetic energy and its influence on eddy momentum fluxes as inferred from altimeter data

Energetics of the Global Ocean: The Role of Mesoscale Eddies

Effects of Eddy Vorticity Forcing on the Mean State of the Kuroshio Extension

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