Mean Antarctic Circumpolar Current transport measured in Drake Passage

Donohue, Kathleen; Tracey, Karen L.; Watts, D. Randolph; Chidichimo, María Paz; Chereskin, Teresa K.

doi:10.1002/2016gl070319

Cited by 222 publications

(238 citation statements)

References 30 publications

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“…For example, the implied transport through a meridional section 1000 km long is over 3 × 10 9 m 3 s −1 ; this is larger by a factor of about twenty than the observed transport of the Antarctic Circumpolar Current (Koenig et al 2016;Donohue et al 2016).…”

Section: Topography Parameter Values and Illustrative Solutionsmentioning

confidence: 83%

Beta-plane turbulence above monoscale topography

Constantinou

Young

2017

J. Fluid Mech.

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Using a one-layer quasi-geostrophic model, we study the effect of random monoscale topography on forced beta-plane turbulence. The forcing is a uniform steady wind stress that produces both a uniform large-scale zonal flow U (t) and smaller-scale macroturbulence characterized by both standing and transient eddies. The large-scale flow U is retarded by a combination of Ekman drag and the domain-averaged topographic form stress produced by the eddies. The topographic form stress typically balances most of the applied wind stress, while the Ekman drag provides all of the energy dissipation required to balance the wind work. A collection of statistically equilibrated numerical solutions delineates the main flow regimes and the dependence of the time-average of U on parameters such as the planetary vorticity gradient β and the statistical properties of the topography. We obtain asymptotic scaling laws for the strength of the large-scale flow U in the limiting cases of weak and strong forcing.If β is significantly smaller than the topographic PV gradient then the flow consists of stagnant pools attached to pockets of closed geostrophic contours. The stagnant dead zones are bordered by jets and the flow through the domain is concentrated into a narrow channel of open geostrophic contours. In most of the domain the flow is weak and thus the large-scale flow U is an unoccupied mean.If β is comparable to, or larger than, the topographic PV gradient then all geostrophic contours are open and the flow is uniformly distributed throughout the domain. In this open-contour case there is an "eddy saturation" regime in which U is insensitive to large changes in the wind stress. We show that eddy saturation requires strong transient eddies that act effectively as PV diffusion. This PV diffusion does not alter the kinetic energy of the standing eddies, but it does increase the topographic form stress by enhancing the correlation between topographic slope and the standing-eddy pressure field. Using bounds based on the energy and enstrophy power integrals we show that as the strength of the wind stress increases the flow transitions from a regime in which most of the form stress balances the wind stress to a regime in which the form stress is very small and large transport ensues.

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Section: Topography Parameter Values and Illustrative Solutionsmentioning

confidence: 83%

Beta-plane turbulence above monoscale topography

Constantinou

Young

2017

J. Fluid Mech.

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“…Munk and Palmén, 1951;Rintoul et al, 2001). Yet, very small residuals below 0.2 nT are found east of the Drake Passage (lower right quadrant of top left panel), which connects the tip of South America and the Antarctic Peninsula, although large mean transports of more than 170 Sv (1 Sv = 10 6 m 3 s −1 ) can occur in this area (Donohue et al, 2016). In this region, however, the ACC flow is almost perpendicular to the gradient of the geomagnetic core field (not shown), resulting in weak oceanic electric currents and induced magnetic signals, regardless of the considered scenario (compare all panels in Fig.…”

Section: Experiments Designmentioning

confidence: 99%

Depth of origin of ocean-circulation-induced magnetic signals

2018

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Abstract. As the world ocean moves through the ambient geomagnetic core field, electric currents are generated in the entire ocean basin. These oceanic electric currents induce weak magnetic signals that are principally observable outside of the ocean and allow inferences about large-scale oceanic transports of water, heat, and salinity. The ocean-induced magnetic field is an integral quantity and, to first order, it is proportional to depth-integrated and conductivity-weighted ocean currents. However, the specific contribution of oceanic transports at different depths to the motional induction process remains unclear and is examined in this study. We show that large-scale motional induction due to the general ocean circulation is dominantly generated by ocean currents in the upper 2000 m of the ocean basin. In particular, our findings allow relating regional patterns of the oceanic magnetic field to corresponding oceanic transports at different depths. Ocean currents below 3000 m, in contrast, only contribute a small fraction to the ocean-induced magnetic signal strength with values up to 0.2 nT at sea surface and less than 0.1 nT at the Swarm satellite altitude. Thereby, potential satellite observations of ocean-circulation-induced magnetic signals are found to be likely insensitive to deep ocean currents. Furthermore, it is shown that annual temporal variations of the ocean-induced magnetic field in the region of the Antarctic Circumpolar Current contain information about sub-surface ocean currents below 1000 m with intra-annual periods. Specifically, ocean currents with sub-monthly periods dominate the annual temporal variability of the oceaninduced magnetic field.

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“…However, as discussed in Sect. 3.5, CORE-II and CMIP ensembles underestimate more recent ACC transport estimates by Donohue et al (2016) and de Verdiére and Ollitrault (2016).…”

Section: The Southern Oceanmentioning

confidence: 99%

“…Recent estimations from Donohue et al (2016), based on 2007-2011 extensive mooring measurements, and from de Verdiére and Ollitrault (2016), based on time-mean Argo float displacements and historical hydrography from the World Ocean Atlas 2009 are likely to be the most reliable ones. Compared to earlier studies, they used methods that reduce uncertainties in the barotropic flow component due to more comprehensive monitoring array and by global mass conserving mean circulation.…”

Section: Liquid Ocean Transportsmentioning

confidence: 99%

An assessment of ten ocean reanalyses in the polar regions

et al. 2018

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Global and regional ocean and sea ice reanalysis products (ORAs) are increasingly used in polar research, but their quality remains to be systematically assessed. To address this, the Polar ORA Intercomparison Project (Polar ORA-IP) has been established following on from the ORA-IP project. Several aspects of ten selected ORAs in the Arctic and Antarctic were addressed by concentrating on comparing their mean states in terms of snow, sea ice, ocean transports and hydrography. Most polar diagnostics were carried out for the first time in such an extensive set of ORAs. For the multi-ORA mean state, we found that deviations from observations were typically smaller than individual ORA anomalies, often attributed to offsetting biases of individual ORAs. The ORA ensemble mean therefore appears to be a useful product and while knowing its main deficiencies and recognising its restrictions, it can be used to gain useful information on the physical state of the polar marine environment.

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Mean Antarctic Circumpolar Current transport measured in Drake Passage

Cited by 222 publications

References 30 publications

Beta-plane turbulence above monoscale topography

Beta-plane turbulence above monoscale topography

Depth of origin of ocean-circulation-induced magnetic signals

An assessment of ten ocean reanalyses in the polar regions

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