DYNAMO : Sigma-coordinate, Z-level, and isopycnic ocean models. 1/3 o resolution. North Atlantic
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Transcript of DYNAMO : Sigma-coordinate, Z-level, and isopycnic ocean models. 1/3 o resolution. North Atlantic
How topographic smoothing contributes to differences between the eddy flows simulated
by sigma- and z-level models.
T. Penduff Center for Ocean-Atmospheric
Prediction studies,
Tallahassee, FL, USA
B. Barnier, Laboratoire des Ecoulements
M.-A. Kerbiriou Geophysiques et Industriels
J. Verron Grenoble, France.
DYNAMO: Sigma-coordinate, Z-level, and isopycnic
ocean models. 1/3o resolution. North Atlantic
THIS STUDY:Sigma-coordinate, Z-level ocean models
1/3o resolution. South Atlantic
Why do the eddy flows simulated by SPEM and OPA differ?
What is the impact of their different topographies?
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South Atlantic configurations
Z-level OPA8.1
Sigma-coord SPEM5.1
• ROUGH bathymetry
+ 3 smoothed bathymetries
• SMOOTHED bathymetry
Same horizontal resolution 1/3o
Same open boundary conditions
Same climatological forcing (ECMWF)
Similar domains
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ROUGH SPEM
Beranger, 2000
Buffer zone
Simple sea-ice model
EKE(z)
Intrinsic or topographically-induced differences???
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Absolute
Relative to 350 m
Subtropical
ACC
Subtropical
ACC
SPEM
ROUGH
EKE(z)
Significant topographically-induced differences.Near-coast processes? Sea-floor roughness?
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Absolute
Relative to 350 m
Subtropical
ACC
Subtropical
ACC
SPEM
ROUGH
GS
Impact of mesoscaletopographic roughness in OPA
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• Reduces eddy-topography interaction• Increases lifetime of Agulhas Rings
GS GSR
GS GSR
The removal of seafloor roughness in SPEM topography explains:• most of OPA/SPEM differences south of 40oS• part of north
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GS GSR
Impact of Seafloor roughness in OPAAbsolute
Relative to 350 m
SPEM
ROUGH
GS
GSR
Subtropical
ACC
Subtropical
ACC
Conclusions
• Different eddy flows in SIGMA and LEVEL
topographies
• Local topographic smoothing in the Agulhas region makes
LEVEL Rings behave like those in SIGMA
• Removing mesoscale roughness makes LEVEL EKE(z)
similar to that in SIGMA
more realistic
• Seemingly intrinsic differences between models in
WBC system
Confluence region
Some smoothing may improve LEVEL solutions in the absence
of adequate parameterization of current-topography interaction
Perspectives
• Eddy-resolving models, other domains ?
• Along-slope currents in sigma- and z-level systems
• Parameterization of topographic effects
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