Structure and Variability of Sub-Antarctic Front Currents Southwest of Tasmania

Douglas S. Luther, Univ. of Hawaii at Manoa, Honolulu, Hawaii
D. Randolph Watts, Univ. of Rhode Island, Kingston, Rhode Is.
Alan D. Chave, Woods Hole Oceanographic Institution, Woods Hole, Mass.
Mathew E. Maltrud, Los Alamos National Laboratory, Los Alamos, New Mexico
James G. Richman, Oregon State Univ., Corvallis, Oregon
Julie McClean Naval Postgraduate School, Dept. Oceanography, Monterey, Calif.
Stephen R. Rintoul, CSIRO Marine Laboratories, Hobart, Australia
John A. Church, CSIRO Marine Laboratories, Hobart, Australia

Abstract:

Observations of the currents associated with the Sub-Antarctic Front (SAF) southwest of Tasmania reveal a mean current structure that is locally divergent meridionally with a northeast tendency to part of the flow that evokes a "standing wave" description. The mean currents and their variability, including integrated transport fluctuations, observed during the two-year-long Sub-Antarctic Flux and Dynamics Experiment (SAFDE) will be described and contrasted with both observations from the WOCE SR3 repeat hydrographic section and output from (at least) the Los Alamos National Laboratory's Parallel Ocean Program (POP) GCM driven with known winds for the SAFDE time period.

The suite of instruments deployed in SAFDE incorporates both well-established ideas of oceanographic experimentation, as well as novel approaches. The former is represented by a seven-element current meter mooring array, where each sub-surface mooring supports 1-5 current meters and up to 2 additional temperature sensors from 300 m to as deep as 3200 m. Straddling this local dynamics array, and extending approximately 450 km along a NNE-SSW line, is an array of 12 horizontal electrometers (HEMs) and 18 inverted echo sounders (IESs). These seafloor instruments are well suited for observing currents at mid- to high latitudes where large vertical scales dominate. The HEMs alone provide direct measurements of the horizontal transport (barotropic) components. The IESs and HEMs combined provide, at least, both horizontal components of a barotropic and (empirical) gravest baroclinic mode description of the horizontal current field.

For additional information about SAFDE, see the web page http://www.soest.hawaii.edu/oceanography/dluther/SAFDE/index.html. For additional information about the LANL POP model, see the web page http://www.acl.lanl.gov/GrandChal/GCM/gcm.html.