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CSIRO Marine and Atmospheric Research
Past Seminars

Seminar Abstract

How water crosses the equatorial vorticity barrier in the eastern pacific

Cross equatorial exchange of water parcels involves a change in sign of Coriolis parameter and therefore also of potential vorticity. This implies a potential vorticity barrier at the equator. However, Sverdrup theory allows for breakage of this barrier, through the curl of the wind stress; an OGCM also shows breakage in the East Pacific, but very different in magnitude and structure from the pure Sverdrup relation. Clearly then, some element of friction or forcing must be added to the water parcels and Kessler et. al. (2003) have shown that the curl of the nonlinear and friction terms do become significant in this region.

Despite considerable efforts in collecting observations over this region, little can be ascertained as to meridional flow due to the large variability in the region (Johnson, McPhaden and Firing 2001). In particular, variability in Tropical Instability Waves is an order of magnitude greater than the mean flow. Models suggest however that this cross hemispheric flow occurs and some (eg. Fukumori 2004) suggest that water parcels are able to cross the equator due to some mechanism associated with intra-annual variations.

We discuss the role of windstress, friction and nonlinearity in this region, on various timescales, and from phenomena such as Tropical Instability Waves. These appear to cause sufficient changes to potential vorticity, allowing cross equatorial flow.

(This talk represents work-in-progress on my PhD. I am keen to get feedback on my results so far and the next steps I should be taking.)

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CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Peter Oke, (Oceanographic seminars) CSIRO Marine Research (03) 6232 5387
Keith Hayes, (Biological seminars) CSIRO Marine Research (03) 6232 5298
Katrina Nitschke, Antarctic Climate and Ecosystems CRC (03) 6226 2265 & IASOS, University of Tasmania (03) 6226 2509