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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

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DYNAMO : Sigma-coordinate, Z-level, and isopycnic ocean models. 1/3 o resolution. North Atlantic

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  1. How topographic smoothing contributes to differences between the eddy flows simulated by sigma- and z-level models. T. PenduffCenter for Ocean-Atmospheric Prediction studies, Tallahassee, FL, USA B. Barnier,Laboratoire des Ecoulements M.-A. KerbiriouGeophysiques et Industriels J. VerronGrenoble, 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? 1

  2. South Atlantic configurations Z-level OPA8.1 Sigma-coord SPEM5.1 • SMOOTHED bathymetry • ROUGH bathymetry • + 3 smoothed bathymetries SPEM ROUGH Buffer zone Beranger, 2000 Simple sea-ice model Same horizontal resolution 1/3o Same open boundary conditions Same climatological forcing (ECMWF) Similar domains 2

  3. Eddy field in ROUGH and SPEM Snapshots of T(300 m) SPEM ROUGH Mean Surface EKE ROUGH SPEM 3

  4. EKE(z) Absolute Subtropical SPEM ROUGH ACC Relative to 350 m Subtropical ACC Intrinsic or topographically-induced differences??? 4

  5. Global topographic smoothing in OPA ROUGH GS 5

  6. ROUGH GS Snapshots of T(300 m) ROUGH GS SPEM 6

  7. Surface EKE ROUGH GS SPEM 7

  8. EKE(z) Absolute Subtropical SPEM ROUGH GS ACC Relative to 350 m Subtropical ACC Significant topographically-induced differences. Near-coast processes? Sea-floor roughness? 8

  9. Local topographic smoothing in OPA ROUGH LS 9

  10. Snapshots of T(300 m) ROUGH LS GS SPEM 10

  11. GS Surface EKE ROUGH LS 11

  12. Impact of mesoscale topographic roughness in OPA GS GSR GS GSR • Reduces eddy-topography interaction • Increases lifetime of Agulhas Rings 12

  13. Impact of Seafloor roughness in OPA Absolute GS GSR Subtropical SPEM ROUGH GS GSR ACC Relative to 350 m Subtropical ACC • The removal of seafloor roughness in SPEM topography explains: • most of OPA/SPEM differences south of 40oS • part of north 13

  14. 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 14

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