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SUMMARY:Understanding global patterns of mesoscale eddy properties and dif
 fusivities - Andreas Klocker (Australian National University)
DTSTART:20131127T110000Z
DTEND:20131127T120000Z
UID:TALK47240@talks.cam.ac.uk
CONTACT:Dr Dan Jones
DESCRIPTION:Geostrophic eddies influence the transport of heat\, carbon an
 d other climatically important tracers in the global ocean. The rate of ed
 dy mixing is typically quantified through an eddy diffusivity. In coarse r
 esolution ocean models\, which are not capable of resolving these eddies\,
  the mixing done by geostrophic eddies has to be parameterised. Yet in the
 ir quest to resolve many topical climate problems\, the models’ credibil
 ity is challenged by their extreme sensitivity to the representation of th
 ese parameterisations. One of the main challenges in developing eddy param
 eterisations is to understand the spatial and temporal variability of eddy
  diffusion coefficients and their relationship to variables available from
  the coarse-resolution ocean model. \n\nIn this talk we will use satellite
 -derived geostrophic velocity fields to directly simulate the evolution of
  passive tracers. From these simulations we calculate eddy diffusivities a
 nd show how these results relate to properties available from coarse-resol
 ution ocean models. To achieve this\, we will use mixing length theory\, m
 odified to account for the suppression of eddy mixing by mean flows and wa
 ve propagation\, to determine the relevant mixing lengths. These results s
 how that a) mixing lengths are proportional to the size of eddies\, and no
 t proportional to the Rossby deformation radius as previously thought\, b)
  eddies move at a phase speed determined by linear Rossby wave theory and 
 c) once the actual size of eddies is known\, eddy diffusion coefficients c
 an be accurately predicted from mean flow properties.
LOCATION:British Antarctic Survey\, Room 307
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