Does the Ulleung eddy owe its existence to β and nonlinearities?

Arruda, Wilton Zumpichiatti; Nof, Doron; O’Brien, James J.

doi:10.1016/j.dsr.2004.07.014

Cited by 23 publications

(17 citation statements)

References 35 publications

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“…This expression is similar to expressions presented in Arruda et al (2004). The equation's first term represents a rocket force exerted in the domain by the northward current, which corresponds to the thick black NC arrow in Fig.…”

Section: Figsupporting

confidence: 70%

“…Lebedev and Nof 1997;Witter and Gordon 1999;Wainer et al 2000;Lentini et al 2002). The study of Arruda et al (2004) suggests that temporal variations in BC transport upstream of the zone can affect the detachment of intrusion eddies at the BMCZ. The shedding of Agulhas rings and their eventual coalescence with the BC may, through a transoceanic ''domino effect,'' contribute to the observed variability.…”

Section: September 2012mentioning

confidence: 98%

“…Following Arruda et al (2004), it is assumed that c 5 c ' (y) and h 5 h ' (y) when x / '. Because the current thickness at the DFC fronts is zero and c ' 5 0 on the southern side of the current, Eq.…”

Section: Figmentioning

confidence: 99%

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Eddy-Train Encounters with a Continental Boundary: A South Atlantic Case Study

Azevedo

Nof

Mata

2012

Journal of Physical Oceanography

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Satellite altimetry suggests that large anticyclonic eddies (rings) originating from the Agulhas Current retroflection occasionally make their way across the entire South Atlantic Ocean. What happens when these rings encounter a western boundary current? In this work, interactions between a ''train'' of nonlinear lenslike eddies and a Southern Hemisphere continental boundary are investigated analytically and numerically on a b plane. The train of eddies is modeled as a steady double-frontal zonal current with the same vorticity and transport as the eddies themselves. The continental boundary is represented by a vertical wall, which is purely meridional in one case and is tilted with respect to the north in another case. It is demonstrated analytically that the eddy-wall encounter produces an equatorward flow parallel to the continental wall, thus suggesting a weakening of the transport of the associated (poleward flowing) western boundary current upstream of the encounter zone and unchanged transport downstream. A large stationary eddy is established in the contact zone because its b-induced force is necessary to balance the other forces along the wall. The size of this eddy is directly proportional to the transport of the eddy train and the meridional tilt of the wall. These scenarios are in good agreement with results obtained numerically using an isopycnal Bleck and Boudra model.

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Section: Figsupporting

confidence: 70%

Section: September 2012mentioning

confidence: 98%

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Eddy-Train Encounters with a Continental Boundary: A South Atlantic Case Study

Azevedo

Nof

Mata

2012

Journal of Physical Oceanography

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“…A critical coastline slant was defined, below which there is rings shedding and above which there is almost no shedding. Indeed, in the case of a meridionally directed incident current, no eddy detachment has been found in numerical models (Arruda et al, 2004). …”

Section: Theoretical Backgroundmentioning

confidence: 99%

Retroflection from a double-slanted coastline: a model for the Agulhas leakage variability

2010

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Abstract. The Agulhas leakage to the South Atlantic exhibits a strong anti-correlation with the mass flux of the Agulhas Current. When the Agulhas retroflection is in its normal position near Cape Agulhas, leakage is relatively high and the nearby South African coastal slant (angle of derivation from zonal) is very small and relatively invariant alongshore. During periods of strong incoming flux (low leakage), the retroflection shifts upstream to Port Elizabeth or East London, where the coastline shape has a "kink", i.e., the slant changes abruptly from small on the west side, to large (about 55 • ) on the east side. Here, we show that the variability of rings shedding and anti-correlation between Agulhas mass flux and leakage to the South Atlantic may be attributed to this kink.To do so, we develop a nonlinear analytical model for retroflection near a coastline that consists of two sections, a zonal western section and a strongly slanted eastern section. The principal difference between this and the model of a straight slanted coast (discussed in our earlier papers) is that, here, free purely westward propagation of eddies along the zonal coastline section is allowed. This introduces an interesting situation in which strong slant of the coast east of the kink prohibits the formation and shedding of rings, while the almost zonal coastal orientation west of the kink encourages shedding. Therefore, the kink "locks" the position of the retroflection, forcing it to occur just downstream of the kink. Rings are necessarily shed from the retroflection area in our kinked model, regardless of the degree of eastern coast slant. In contrast, a no-kink model with a coastline of intermediate slant indicates that shedding is almost completely arrested by that slant.Correspondence to: D. Nof (nof@ocean.fsu.edu)We suggest that the observed difference in ring-shedding intensity during times of normal retroflection position and times when the retroflection is shifted eastward is due to the change in the retroflection location with respect to the kink. When the incoming flux detaches from the coast north of the kink, ring transport is small; when the flux detaches south of the kink, transport is large. Simple process-oriented numerical simulations are in fair agreement with our analytical results.

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“…ε = βR d /f characterizes the variation of the Coriolis parameter (due to β) at the scale of the eddy's Rossby radius R d (see, e.g. Arruda et al, 2004). In this approximation, we assume that the BE is circular, and that the incoming and outgoing fluxes are geostrophic in the cross-stream direction.…”

Section: Statement Of Problemmentioning

confidence: 99%

The arrested Agulhas retroflection

Nof¹,

Zharkov²,

Ortiz³

et al. 2011

j mar res

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Paleoceanographic proxy data indicate that the Agulhas leakage into the South Atlantic was dramatically reduced during glacial times. In our former papers, we suggested that this was due to a northward shift of the zero wind stress curl that, in turn, forced the retroflection to occur farther north, where the slant of the coastline relative to the north is steep. In the present paper, we propose that strong westerlies (0.4 Pa, implying a wind speed of ∼12 m s −1 at zero degrees centigrade), which were supposedly common during glaciations, can also arrest the leakage. This arrest occurred because the wind stress opposed the momentum flux associated with the retroflection; such an arrest did not require the retroflection to shift in latitude.We use a simple, nonlinear, "reduced gravity" model to show analytically and numerically that, under the above conditions, the eastward wind stress compensates for the zonal westward flow-force associated with the retroflection, thus avoiding the development and shedding of rings. For a nearly zonal wall, westerly winds, and small upper layer thickness along the wall, the arresting wind stress is found, theoretically, to be, τ x = 0.042α 3/2 ρf 0 [(2f 0 Q) 3 /g ] 1/4 , where α is twice the retroflection eddy vorticity, ρ is the water density, Q is the Agulhas Current volume flux, and the remaining notation is conventional. A few words on Stern's contribution to the field of eddiesEddies, the oceanic analogs of tornadoes and hurricanes, were one of Melvin's specialties. In an elegant paper that most people originally referred to as "esoteric" (1974, JMR), Melvin showed that much can be learned about eddies by looking at groups of two adjacent vortices, each spinning in a different direction. For reasons known only to him, he coined this counter-spinning vortex a "Modon". (A modon actually means a collection of cities in Arabic.) Despite the initial skepticism by some (evidently, one editor of a respectable 1.

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Does the Ulleung eddy owe its existence to β and nonlinearities?

Cited by 23 publications

References 35 publications

Eddy-Train Encounters with a Continental Boundary: A South Atlantic Case Study

Eddy-Train Encounters with a Continental Boundary: A South Atlantic Case Study

Retroflection from a double-slanted coastline: a model for the Agulhas leakage variability

The arrested Agulhas retroflection

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