Hobart

Seminar Abstract

Friday 17 October 2008, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Ken Ridgway
Centre for Australian Weather and Climate Research
A partnership between CSIRO and the Bureau of Meteorology

Constructing ocean climatological fields from Argo floats, and satellite altimetry*

Climatological fields of oceanic properties are a major resource for characterizing ocean regions. A variety of methods have been employed to extract the ‘best estimate’ of the mean structure from the distribution of raw observations. However, in general the in situ data archives have not had sufficient spatial and temporal coverage to adequately resolve eddies, frontal regions and boundary currents and hence climatological fields have been produced with high levels of smoothing. Furthermore to realistically represent the oceanic condition within a set period, say a decade, such mean fields should be based on data collected within the same period. However, due to a combination of the high natural variability at small spatial scales and the general scarcity of data, most of the existing climatologies have been generated by averaging data from several decades resulting in very smooth fields with an unrealistic representation of boundary currents and other small scale features. We present results from a suite of methods using in situ data, and satellite observations to obtain an enhanced set of climatological fields of oceanic properties for a time-specific period. The dramatic build-up of global Argo profiles provides repeated measurements and coverage in previously under-sampled regions. However, shortcomings still exist in this greatly improved data distribution. High variability western boundary current eddy fields, continental slope and shelf boundaries and topographic complex regions may be below their optimal sampling requirements from purely in situ data sources. We describe several simple methods to supplement and improve standard interpolation schemes and apply them to the available data within the waters surrounding Australia. This region includes a major current system, the East Australian Current, complex topography, unique boundary currents (Leeuwin Current, Zeehan Current) and large ENSO related interannnual variability in the southwest Pacific. We use satellite altimetry sea level anomalies (SLA) to directly correct sampling errors in in situ derived mean surface steric height and subsurface temperature and salinity fields. The surface correction is projected through the water column (using an empirical model) to modify the subsurface T and S fields. A ‘baroclinic factor’ to convert the altimetry SLA into an equivalent in situ height is determined. The spatial distribution of the barotropic- baroclinic balance is obtained for the region. Initial results are also presented from a model run which is strongly nudged to the climatological fields. The errors inherent in all these calculations are examined and the results compared with simply expanding the correlation length scale (increased smoothing) - how much realistic extra spatial structure may be extracted? The mean fields in the EAC region are compared with independent estimates on repeated XBT sections, a mooring array and full-depth CTD transects.

* Ken Ridgway and Jeff Dunn, Centre for Australian Weather and Climate Research, A partnership between CSIRO and the Bureau of Meteorology

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