Dynamics of the Leeuwin Current: Part 1. Coastal flows in an inviscid, variable-density, layer model

Furue, Ryo; McCreary, Julian P.; Benthuysen, Jessica A.; Phillips, Helen E.; Bindoff, Nathaniel L.

doi:10.1016/j.dynatmoce.2013.03.003

Cited by 44 publications

(39 citation statements)

References 30 publications

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“…The first is the Indonesian Throughflow (ITF), which raises sea level north of Australia; the higher sea level extends southward along the WA coast through the propagation of coastally trapped waves, thereby establishing a zonal-pressure-gradient field that drives the LC (e.g., Godfrey and Ridgway 1985;Kundu and McCreary 1986). The second is near-surface, eastward flow across the interior of the SIO [section 1a(3)], which bends southward at the WA coast to form the LC Thompson 1987;Weaver andMiddleton 1989, 1990;Furue et al 2013;Benthuysen et al 2014;Lambert et al 2016). A general result from the second mechanism is that a southward-flowing LC can be produced, provided the onshore interior transport is large enough to overwhelm offshore Ekman drift driven by the prevailing southerly winds.…”

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confidence: 95%

“…The LC is clearly defined in all the sections as the region of negative flow (blue shading) adjacent to the continental slope above 200 m. Very near the coast where D , 100 m, the equatorward-flowing Ningaloo (228-248S) and Capes (298-348S) Currents (Fig. 3), which are driven by the southerly alongshore winds Pearce and Pattiaratchi 1999;Woo et al 2006;Furue et al 2013), are also visible, although their accuracy is dubious. For one thing, error of the geostrophic calculation is not small in shallow waters (Fig.…”

Section: ) Vertical Structurementioning

confidence: 99%

“…Finally, the LUC is linked to the westward, subsurface flows in the interior of the SIO, with LUC water diverging from the coast to supply water for the westward SIO flow. One limitation of the two models is that they lack a continental shelf, which is known to weaken (inhibit) offshore Rossby-wave propagation (Weaver and Middleton 1990;Furue et al 2013;Benthuysen et al 2014), and without shelf topography, the model LC and LUC are necessarily aligned vertically with equal and opposite transports, whereas the real LUC tends to be shifted offshore. Another limitation is that, unless diffusion is sufficiently strong (perhaps unrealistically so), both the LC and LUC are weak and the LUC does not extend deep enough into the water column.…”

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confidence: 99%

“…In the Kundu and McCreary (1986) and McCreary et al (1986) models, coastal trapping results from vertical diffusion, which damps Rossby waves associated with higherorder vertical modes before they can propagate very far offshore. In the Weaver and Middleton (1989Middleton ( , 1990, Furue et al (2013), and Benthuysen et al (2014) solutions, it is caused by the continental slope, which traps Rossby waves to the coast by the topographic b effect.…”

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confidence: 99%

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On the Leeuwin Current System and Its Linkage to Zonal Flows in the South Indian Ocean as Inferred from a Gridded Hydrography

Furue

Guerreiro

Phillips

et al. 2017

Journal of Physical Oceanography

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The Leeuwin Current System (LCS) along the coast of Western Australia consists of the poleward-flowing Leeuwin Current (LC), the equatorward-flowing Leeuwin Undercurrent (LUC), and neighboring flows in the south Indian Ocean (SIO). Using geostrophic currents obtained from a highly resolved ( 1 /88) hydrographic climatology [CSIRO Atlas of Regional Seas (CARS)], this study describes the spatial structure and annual variability of the LC, LUC, and SIO zonal currents, estimates their transports, and identifies linkages among them. In CARS, the LC is supplied partly by water from the tropics (an annual mean of 0.3 Sv; 1 Sv [ 10 6 m 3 s 21 ) but mostly by shallow (&200 m) eastward flows in the SIO (4.7 Sv), and it loses water by downwelling across the bottom of this layer (3.4 Sv). The downwelling is so strong that, despite the large SIO inflow, the horizontal transport of the LC does not much increase to the south (from 0.3 Sv at 228S to 1.5 Sv at 348S). This LC transport is significantly smaller than previously reported. The LUC is supplied by water from south of Australia (0.2 Sv), by eastward inflow from the SIO south of 288S (1.6 Sv), and by the downwelling from the LC (1.6 Sv) and in response strengthens northward, reaching a maximum near 288S (3.4 Sv). North of 288S it loses water by outflow into subsurface westward flow (23.6 Sv between 288 and 228S) and despite an additional downwelling from the LC (1.9 Sv), it decreases to the north (1.7 Sv at 228S). The seasonality of the LUC is described for the first time.

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confidence: 95%

Section: ) Vertical Structurementioning

confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

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On the Leeuwin Current System and Its Linkage to Zonal Flows in the South Indian Ocean as Inferred from a Gridded Hydrography

Furue

Guerreiro

Phillips

et al. 2017

Journal of Physical Oceanography

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“…Theories on the coastal trapping of the LC have focused on vertical diffusion of Rossby waves (McCreary et al, 1986) and interaction with the continental shelf (Csanady, 1978(Csanady, , 1985. An ongoing programme is evaluating these various proposed mechanisms (Furue et al, 2013;Benthuysen et al, 2014) but leaves the problem of large-scale forcing and connectivity of the LC unanswered. To understand this large-scale forcing, one needs to understand the origin of the off-shore meridional gradients, which hints at an important role of the SICC.…”

Section: Introductionmentioning

confidence: 99%

The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

2016

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Abstract. East of Madagascar, the shallow "South Indian Ocean Counter Current (SICC)" flows from west to east across the Indian Ocean against the direction of the winddriven circulation. The SICC impinges on west Australia and enhances the sea level slope, strengthening the alongshore coastal jet: the Leeuwin Current (LC), which flows poleward along Australia. An observed transport maximum of the LC around 22 • S can likely be attributed to this impingement of the SICC. The LC is often described as a regional coastal current that is forced by an offshore meridional density gradient or sea surface slope. However, little is known about the controls of these open-ocean gradients. The regional circulation system is embedded in the subtropical "super gyre" that connects the Indo-Pacific via the Tasman Gateway and the Indonesian passages. The Indonesian Throughflow (ITF) circulates through the Indian Ocean back into the Pacific south of Australia. This return pathway appears to be partly trapped in the upper layer north of an outcrop line. It is redirected along this outcrop line and joins the eastward flow of the SICC. To study the connection of the basin-scale and the inter-oceanscale dynamics, we apply both an ocean general circulation model and a conceptual two-layer model. Shutdown of the ITF in the models leads to a large decrease in Leeuwin Current transport. Most of the SICC was found to then reconnect to the internal gyre circulation in the Indian Ocean. ITF, SICC and LC thus appear to be dynamically connected.

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Salinity dominance on the Indian Ocean Eastern Gyral current

Menezes

Phillips

Schiller

et al. 2013

Geophysical Research Letters

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This study demonstrates the importance of salinity gradients to the formation of the Eastern Gyral Current (EGC) in the South Indian Ocean. The EGC flows eastward near 15∘S, opposite to the direction predicted by classical theories of wind‐driven circulation and is a source of water for the Leeuwin Current. In the upper ocean, a strong salinity front exists between fresh water from the Indonesian Throughflow (ITF) in the South Equatorial Current (SEC) and salty subtropical waters. In that region, salinity overwhelms the temperature contribution to density gradients, generating eastward geostrophic shear and establishing the EGC. Without the salinity front the EGC cannot be maintained: If the salinity contribution is neglected in the calculation of geostrophic currents, the EGC vanishes. Our observational analysis associated with the fact that both Sverdrup and Ekman theories produce westward flows in the region strongly supports the idea that the EGC is a salinity‐driven current.

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Dynamics of the Leeuwin Current: Part 1. Coastal flows in an inviscid, variable-density, layer model

Cited by 44 publications

References 30 publications

On the Leeuwin Current System and Its Linkage to Zonal Flows in the South Indian Ocean as Inferred from a Gridded Hydrography

On the Leeuwin Current System and Its Linkage to Zonal Flows in the South Indian Ocean as Inferred from a Gridded Hydrography

The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current

Salinity dominance on the Indian Ocean Eastern Gyral current

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