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Model Comparison and Evaluation Studies

TOMS Inaugural Meeting, NCAR, Aug. 23, 2001. Model Comparison and Evaluation Studies. Tal Ezer (with H. Arango & A. Shchepetkin). Goal: to evaluate and test new numerical elements in terrain-following ocean models.

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Model Comparison and Evaluation Studies

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  1. TOMS Inaugural Meeting, NCAR, Aug. 23, 2001 Model Comparison and Evaluation Studies Tal Ezer (with H. Arango & A. Shchepetkin)

  2. Goal: to evaluate and test new numerical elements in terrain-following ocean models. • Why: to help developers in improving codes and users in selecting options and parameterizations. • How: by comparing different schemes and parameterizations in POM and ROMS/TOMS. • Criteria: numerical errors, accuracy, stability, compatibility between schemes, computational cost.

  3. Tested Elements • Advection schemes • Time stepping algorithms • Pressure gradient schemes • Others

  4. Seamount configuration test Very steep case h=4050m, w=50km s=0.36, r=14.2 moderately steep h=2700m, w=100km s=0.07, r=2.7 S=max(DH/2H) r=max(sDH/HDs) grid=(64x64x20), Dx=8km

  5. Zonal flow -50cm 0 +50cm Topography Sea surface height

  6. Effect of advection scheme on model: Surface elevation anomaly ADV2- 2nd ord. cnt. POM ROMS ADV4- 4th ord. cnt. ADV3- 3rd ord. upst. ROMS ROMS

  7. Time-stepping schemes(split mode: baroclinic/internal and barotropic/external)

  8. Coupling of barotropic (external) and baroclinic (internal) modes in ROMS weights Un+1 = SamUm Un+½ = S bm’Um’ DTE 1<m<N, N=DTI/DTE DTI

  9. Sensitivity to internal (DTI) & external (DTE) time steps ROMS UNSTABLE STABLE TDI/DTE POM CFL=13s

  10. Computational cost for different models & parameterizations

  11. The adjustment process in POM and ROMS: forced case (zonal flow)

  12. Roms- sensitivity of adjustment procesto time step choices DTE=12s DTE=24s DTI=360s DTI=720s

  13. Pressure Gradient Schemes

  14. Structure ofV (cm/s) in ROMS for different PG schemes (medium seamount case) R-DJ (Vmax=3.7) R-PJQ (Vmax=0.03) R-FPJ (Vmax=30) R-DJC (Vmax=0.06) R-WDJ (Vmax=0.3)

  15. PG errors- moderately steep seamount

  16. More model elements and schemes need to be tested • Boundary conditions • Data assimilation • Nesting and air-sea coupling • Horizontal and vertical mixing schemes • Generalized coordinate system: comparisons between sigma, z-level & isopycnal grids.

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