HR: 14:40h
AN: OS43C-05    [Abstracts]
TI: Quantifying Eddy Mixing in the Southern Ocean
AU: * Shuckburgh, E
EM: eshuck@damtp.cam.ac.uk
AF: Univ Cambridge, DAMTP Centre for Mathematical Sciences, Cambridge, CB3 0WA United Kingdom
AU: Marshall, J
EM: marshall@ocean.mit.edu
AF: MIT-EAPS, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Jones, H
EM: helen@ocean.mit.edu
AF: MIT-EAPS, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Hill, C
EM: cnh@mit.edu
AF: MIT-EAPS, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AB: An outstanding problem in large-scale ocean dynamics is the understanding, characterisation and representation of tracer transport by geostrophic eddies. Eddy transport in the coarse resolution ocean models used in climate research is parameterised by assuming that eddy tracer flux is related to mean tracer gradient through an eddy diffusivity. The very assumption of a flux gradient relationship is open to question. Arguably the key uncertainty in these models is lack of knowledge of the magnitude of the diffusivities and their variation in space and time. These matters are further complicated by the fact that eddy transfer has not been well characterised by in-situ measurements. An attempt to arrive at a more definitive estimate of ocean near-surface eddy diffusivities using a method pioneered to diagnose tracer transport in the stratosphere will be described. The transport properties of the eddy field are diagnosed by calculating an `effective diffusivity' diagnostic from a tracer. The technique uses Topex/Poseidon sea-surface altimeter data to derive a geostrophic surface velocity field, which is then used in a numerical model to transport a passive tracer around the Antarctic Circumpolar Current. Using the effective diffusivity diagnsotic, quantify the eddy diffusivity from this tracer field. The results from the application of our technique show high spatial variations in effective diffusivity accross the ACC, with values ranging from a few hundred ($m^2/s$) to several thousand. The implications of these results for the understanding of the residual circulation in the Southern Ocean and eddy parameterisation in models will be discussed.
DE: 4200 OCEANOGRAPHY: GENERAL
DE: 4255 Numerical modeling
DE: 4512 Currents
DE: 4520 Eddies and mesoscale processes
DE: 4532 General circulation
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting