Multiple Jets of the Antarctic Circumpolar Current South of Australia*

Abstract

Maps of the gradient of sea surface height (SSH) and sea surface temperature (SST) reveal that the Antarctic Circumpolar Current (ACC) consists of multiple jets or frontal filaments. The braided and patchy nature of the gradient fields seems at odds with the traditional view, derived from hydrographic sections, that the ACC is made up of three continuous circumpolar fronts. By applying a nonlinear fitting procedure to 638 weekly maps of SSH gradient (١SSH), it is shown that the distribution of maxima in ١SSH (i.e., fronts) is strongly peaked at particular values of absolute SSH (i.e., streamlines). The association between the jets and particular streamlines persists despite strong topographic and eddy-mean flow interactions, which cause the jets to merge, diverge, and fluctuate in intensity along their path. The SSH values corresponding to each frontal branch are nearly constant over the sector of the Southern Ocean between 100°E and 180°. The front positions inferred from SSH agree closely with positions inferred from hydrographic sections using traditional water mass criteria. Recognition of the multiple branches of the Southern Ocean fronts helps to reconcile differences between front locations determined by previous studies. Weekly maps of SSH are used to characterize the structure and variability of the ACC fronts and filaments. The path, width, and intensity of the frontal branches are influenced strongly by the bathymetry. The "meander envelopes" of the fronts are narrow on the northern slope of topographic ridges, where the sloping topography reinforces the ␤ effect, and broader over abyssal plains. * This paper is an addition to the collection of papers published in the February 2007 Journal of Physical Oceanography Special Issue in Honor of Carl Wunsch (see acknowledgments).

Global observations of quasi‐zonal bands in microwave sea surface temperature

“…Referred to as quasi-zonal in reference to their departure from a strictly zonal orientation and latent owing to their O(1 cm s 21 ) magnitude relative to the more dominant O(10 cm s 21 ) eddy field, these jet-like structures have been observed globally [Maximenko et al, 2005[Maximenko et al, , 2008 and regionally in studies involving each or a combination of the aforementioned data sets (altimeter SSH, MDT, and Argo). Regional studies include those in the subtropics Centurioni et al, 2008;Scott et al, 2008;Ivanov et al, 2009Ivanov et al, , 2010van Sebille et al, 2011;Buckingham and Cornillon, 2013], Southern Ocean [Sokolov and Rintoul, 2007] and near-equatorial waters [Cravatte et al, 2012;Qiu et al, 2013]. Some suggestion of their existence is also found within the trajectories of Lagrangian isopycnal floats in the Deep Brazil Basin [Hogg and mesoscale eddies identified and tracked by Chelton et al [2011a] but that two characteristics were inconsistent with their model of random eddies: the (i) variance of u did not decay as expected and (ii) number of eddies, as well as the size and amplitude of these eddies, correlated with the observed jet-like structures was large and broad in spectrum.…”

Zonal jets in equilibrating baroclinic instability on the polar beta‐plane: Experiments with altimetry

“…The geography of the most baroclinically unstable regions includes the Antarctic Circumpolar Current (ACC), and western boundary currents such as the Gulf Stream and Kuroshio and their extensions [Smith, 2007]. Observations show that multiple zonal jets are indeed created in these regions and are quite prominent there [Maximenko et al, 2005[Maximenko et al, , 2008Sokolov and Rintoul, 2007;Thompson, 2008]. Berloff et al [2009aBerloff et al [ , 2009b suggested yet another way which leads to creation of zonal jets.…”

Campbell Plateau: A major control on the SW Pacific sector of the Southern Ocean circulation

“…The SAF forms the northern boundary of the ACC, and carries much of its transport (Gille, 2003;Sokolov and Rintoul, 2007).…”

“…They are forced to pass through gaps in the Macquarie Ridge, and merge where the 10 SAF impinges on Campbell Plateau (e.g., Morris et al, 2001;Sokolov et al, 2006;Rintoul et al, 2014). Downstream, the flow divides into two branches, the northern branch following the plateau bathymetry and the middle and southern branches turning sharply to the south east at ∼ 164°E (e.g., Davis, 1998;Morris et al, 2001;Stanton and Morris, 2004;Sokolov and Rintoul, 2007). However, identification of the Southern Ocean fronts is not a straight forward task.…”