Hobart

Seminar Abstract

Friday 25 June 2010, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Wilbert Weijer
Los Alamos National Laboratory
Los Alamos, New Mexico

Modal variability in the Australian-Antarctic Basin

The Australian-Antarctic Basin (AAB) is known as an area of high sea-surface height (SSH) variability. In this presentation I will address the nature of this variability.

A normal-mode analysis of a barotropic shallow-water model shows two dominant, stationary modes in the AAB. These modes are trapped by closed contours of potential vorticity (f/H), specifically in the eastern AAB (Wilkes Abyssal Plain) and on top of the western Southeast Indian Ridge. Projection of the modal patterns onto time series of a 1000-day model integration shows that these modes decay slowly, reconciling different estimates of the decay time scale in the literature. But more importantly, the analysis shows that these free modes account for only a fraction of the variance in the AAB.

A follow-up analysis shows that the SSH variability may instead be interpreted as a so-called almost-free mode response. Moving largely along contours of potential vorticity, the circulation has to jump contours at certain locations. In particular, the apex of the Wilkes Abyssal Plain appears to be a key location for the decay of this mode. Here, the mode loses most of its energy to non-modal circulation (waves) and friction. The enhanced dissipation of the barotropic circulation in this area may make it a key location for deep ocean mixing.

Seminar recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Tracey Cochrane, Institute for Marine and Antarctic Studies (IMAS), University of Tasmania (03) 6226 2937

Last updated 13/07/10