A Mean Synoptic View of the Subantarctic Front South of Australia

Phillips, Helen E.; Rintoul, Stephen R.

doi:10.1175/1520-0485(2002)032<1536:amsvot>2.0.co;2

Cited by 24 publications

(56 citation statements)

References 27 publications

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“…Hall (1986) instead found the horizontal shear magnitude to be larger on the warm side of the Gulf Stream at a location fairly close to the later Johns et al (1995) study. Phillips and Rintoul (2002) found the largest horizontal shear magnitude on the warm side of the SAF. The results from our best section indicate that the largest horizontal shear magnitude is on the cold side of the SAF (Fig.…”

Section: Example Of Dynamical Implicationsmentioning

confidence: 91%

“…. Possible frozen field distance axes; upper panel shows a canonical cross-stream section of the 6 C isotherm pressure, while the lower panel shows a cross-section of the specific volume anomaly at 780 dbar: The latter is similar to the frozenfield axis used by Phillips and Rintoul (2002).…”

Section: Defining Cross-stream Locationmentioning

confidence: 94%

“…Johns et al, 1995). Other studies have used the midpoint between an isotherm crossing two isobars (Rossby, 1987), a particular specific volume anomaly occurring on a pressure surface (Phillips and Rintoul, 2002), etc. An important consideration with regards to this determination is how the cross-stream distance is going to be determined.…”

Section: Choosing a Stream Coordinates Originmentioning

confidence: 99%

“…If no perpendicular can be drawn (thin black dashed lines), it suggests that the closest point of approach of the core is outside of the IES array, and as such the velocity measurement for that particular site and day cannot be accurately used in determining the stream coordinates structure. Note that while the 2 The original stream coordinates method presented in Hall and Bryden (1985), and used in modified form by Phillips and Rintoul (2002), involved averaging first in temperature bins and used the 'frozen field' only for converting the mean velocity values onto a distance axis. Because averaging is a linear process that method is mathematically identical to the 'frozen field' method applied to the daily data as presented herein.…”

Section: Defining Cross-stream Locationmentioning

confidence: 99%

“…The method generally used to obtain the synoptic structure of a current is the ''stream coordinates'' approach. Stream coordinates techniques have been applied to strong current systems around the world, such as the Gulf Stream (Halkin and Rossby, 1985;Hall, 1986;Hogg, 1992;Johns et al, 1995;Bower and Hogg, 1996), the North Atlantic Current (Meinen, 2001), the Kuroshio extension (Hall, 1989), and the Subantarctic Front (Phillips and Rintoul, 2002).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Comparison of methods of estimating mean synoptic current structure in “stream coordinates” reference frames with an example from the Antarctic Circumpolar Current

Meinen

Luther

2003

Deep Sea Research Part I: Oceanographic Research Papers

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Stream coordinates techniques, that is, methods of deriving the mean ''synoptic'' structures of narrow meandering ocean currents from Eulerian measurements, have been in use for nearly two decades and have resulted in improvements in our understanding of the dynamics and transports of such currents. A 2-year experiment in the SubAntarctic Front (SAF) southwest of Tasmania, involving overlapping arrays of inverted echo sounders and horizontal electric field recorders, has provided an opportunity to test various stream coordinates methods. The methods differ significantly in how well, or even if, they can reveal divergence or convergence of the meandering current, and whether they accurately reproduce the current's horizontal structure and transport. Cross-stream distance was determined either via a frozen-field assumption or as the distance to an optimally interpolated (OI) origin contour; downstream direction was determined either as the local direction which maximized the vertical shear of horizontal velocity or as the tangent line to the OI mapped core contour. All combinations of these distance and direction definitions were tested. The use of a frozen field assumption in determining cross-stream distance yields overly smooth along-stream velocity cross-sections and overestimated transports. The vertical shear definition of downstream direction results in a false rotation of crossstream flows into along-stream flows near the flanks of the current. The preferred methods define the horizontal location of the front with 2-D arrays of instruments (e.g., inverted echo sounders or moored current meters). Methods employing the assumptions of a meandering ''frozen-field'' baroclinic structure or the use of the local vertical shear of the horizontal velocity to determine the downstream direction should be avoided, if possible, particularly in the SAF. r

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Section: Example Of Dynamical Implicationsmentioning

confidence: 91%

Section: Defining Cross-stream Locationmentioning

confidence: 94%

Section: Choosing a Stream Coordinates Originmentioning

confidence: 99%

Section: Defining Cross-stream Locationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Comparison of methods of estimating mean synoptic current structure in “stream coordinates” reference frames with an example from the Antarctic Circumpolar Current

Meinen

Luther

2003

Deep Sea Research Part I: Oceanographic Research Papers

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On the nonequivalent barotropic structure of the Antarctic Circumpolar Current: An observational perspective

Phillips

Bindoff

2014

JGR Oceans

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We examine the vertical structure of the horizontal flow and diagnose vertical velocities in the Antarctic Circumpolar Current (ACC) near the Kerguelen Plateau using EM-APEX profiling floats. Eight floats measured horizontal velocity, temperature, and salinity profiles to 1600 dbar, with a vertical spacing of 3-5 dbar four times per day over a period of approximately 3 months. Horizontal velocity profiles show a complex vertical structure with strong rotation of the velocity vector through the water column. The distribution of rotation angles from 1247 profiles is approximately Gaussian and rotations of either sign are equally likely. Forty percent of profiles with speed greater than 5 cm s 21 have a depth-integrated rotation of less than 15 degrees over 1300 dbar, while the other 60% demonstrate significantly stronger rotation. Consequently, most profiles do not conform to the equivalent barotropic model (deep flow parallel and proportional to the surface flow) used in simplified dynamical models and in Gravest Empirical Mode climatologies of the ACC. Nevertheless, since we find the mean rotation to be zero, an equivalent barotropic assumption is valid to first order. Vertical velocities inferred using conservation of mass and a gradient wind balance in natural coordinates have magnitudes on the order of 100 m/day. We find robust patterns of upwelling and downwelling phase-locked to meanders in the flow, as found in earlier studies. With the advent of highresolution observations such as those presented here, and high-resolution models, we can advance to a more complete understanding of the rich variability in ACC structure that is neglected in the equivalent barotropic model.

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Antarctic Circumpolar Current transport and barotropic transition at Macquarie Ridge

Rintoul

Sokolov

Williams

et al. 2014

Geophysical Research Letters

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Theory and numerical simulations suggest that topographic interactions are central to the dynamics of the Antarctic Circumpolar Current (ACC), but few observations are available to test these ideas. We use direct velocity measurements, satellite altimetry, and an ocean state estimate to investigate the interaction of the ACC with the Macquarie Ridge. Satellite altimeter data show that the Subantarctic Front crosses the ridge through a gap immediately north of Macquarie Island. Yearlong current meter records reveal strong deep mean flow (> 0.2 m s À1 at 3000 m) and substantial transport (52 ± 8 × 10 6 m 3 s À1 ) in the 50 km wide gap. The ACC becomes much more barotropic at the ridge. Acceleration of the deep jet is balanced by the ageostrophic along-gap pressure gradient, convergence of zonal momentum by the mean vertical velocity, and dissipation. The study helps explain how the ACC negotiates large topographic obstacles and highlights the role of local, nonlinear processes in the dynamical balance of the ACC.

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A Mean Synoptic View of the Subantarctic Front South of Australia

Cited by 24 publications

References 27 publications

Comparison of methods of estimating mean synoptic current structure in “stream coordinates” reference frames with an example from the Antarctic Circumpolar Current

Comparison of methods of estimating mean synoptic current structure in “stream coordinates” reference frames with an example from the Antarctic Circumpolar Current

On the nonequivalent barotropic structure of the Antarctic Circumpolar Current: An observational perspective

Antarctic Circumpolar Current transport and barotropic transition at Macquarie Ridge

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