Hobart

Seminar Abstract

Friday 19 September 2008, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Andrew Meijers
UTAS/CSIRO/ACE-CRC Oceanography PhD student
IASOS University of Tasmania

Creating and testing a 4-D representation of Southern Ocean temperature, salinity and velocity by combining satellite altimetry with historical hydrography

I present a Gravest Empirical Mode (GEM) projection of historical hydrography over the Southern Ocean and use it in combination with satellite altimetry to produce time-evolving, full-depth temperature, salinity and velocity fields on a regular grid. I will describe the process of creating and testing the GEM fields, which capture over 96% and 90% of the temperature and salinity variance below the thermocline respectively, and resolve front and eddy features significantly more accurately than traditional climatologies in this region. The GEM fields accurately recreate ARGO and ship hydrographic observations.

The full depth temperature and salinity fields allow the calculation of weekly Southern Ocean baroclinic velocity fields at each depth level of the GEM fields. Surface referencing these to altimetry based geostrophic velocities then gives absolute velocities over all depths. The resulting u and v velocity fields correlate with ARGO drift velocities with respective coefficients of 0.58 and 0.48, and closely match observations from the SAFDE current meters in the SubAntarctic Front (SAF) south of Australia.

The T, S, u and v fields allow the calculation of many ocean properties. As an example I will discuss the use of the GEM fields to examine the physically interesting, but observationally difficult, problem of eddy property transports. The GEM performs well at the AUSSAF current meter array where it matches the observational pointwise eddy heat transport in direction and magnitude. The average GEM global cross frontal eddy heat transports are then calculated circumpolarly using two methods. The first uses a traditional statistical decomposition of transports into mean, standing and transient eddy components, while the other explicitly tracks the change in heat content of closed mesoscale eddy rings shed from the fronts. Both methods produce similar mean eddy heat transports of approximately 0.02-0.03 PW southward, increasing to around 0.1 PW at the SAF. I will discuss the spatial distribution of the eddy fluxes, as well as their relation to accepted eddy transport values.

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:
Bernadette Sloyan, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5152
Thomas Kunz, (Biological seminars) CSIRO Marine and Atmospheric Research
(03) 6232 5076
Natalie Dowling, (Fisheries Modelling) CSIRO Marine and Atmospheric Research
(03) 6232 5148
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 21/07/09