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The Polar Front in D rake P assage: A composite‐mean stream‐coordinate view
Author(s) -
Foppert Annie,
Donohue Kathleen A.,
Watts D. Randolph
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2015jc011333
Subject(s) - baroclinity , geology , buoyancy , polar , front (military) , geopotential , geodesy , ridge , potential vorticity , vorticity , physics , atmospheric sciences , climatology , oceanography , mechanics , vortex , paleontology , astronomy
The Polar Front (PF) is studied using 4 years of data collected by a line of current‐ and pressure‐recording inverted echo sounders in Drake Passage complemented with satellite altimetry. The location of the PF is bimodal in latitude. A northern and southern PF exist at separate times, separated geographically by a seafloor ridge—the Shackleton Fracture Zone—and hydrographically by 17 cm of geopotential height. Expressed in stream coordinates, vertical structures of buoyancy are determined with a gravest empirical mode analysis. Baroclinic velocity referenced to zero at 3500 dbar, width, and full transport (about 70 Sv) of the jets are statistically indistinguishable; the two jets alternate carrying the baroclinic transport rather than coexisting. Influences of local bathymetry and deep cyclogenesis manifest as differences in deep reference velocity structures. Downstream reference velocities of the PF‐N and PF‐S reach maximum speeds of 0.09 and 0.06 m s −1 , respectively. Buoyancy fields are indicative of upwelling and poleward residual circulation at the PF. Based on potential vorticity and mixing lengths, the northern and southern PF both act as a barrier to cross‐frontal exchange while remaining susceptible to baroclinic instability.