University of Tasmania
Browse

File(s) under permanent embargo

On the non-equivalent barotropic structure of the Antarctic Circumpolar Current: an observational perspective

journal contribution
posted on 2023-05-18, 02:15 authored by Helen PhillipsHelen Phillips, Nathaniel BindoffNathaniel Bindoff
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 cms-1 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 dynamic 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 high-resolution 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.

Funding

Australian Research Council

History

Publication title

Journal of Geophysical Research: Oceans

Volume

119

Issue

8

Pagination

5221-5243

ISSN

2169-9275

Department/School

Institute for Marine and Antarctic Studies

Publisher

Amer Geophysical Union

Place of publication

2000 Florida Ave Nw, Washington, USA, Dc, 20009

Rights statement

Copyright 2014 American Geophysical Union

Repository Status

  • Restricted

Socio-economic Objectives

Climate variability (excl. social impacts)

Usage metrics

    University Of Tasmania

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC