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Comparisons of Numerical Aspects in POM and ROMS

Comparisons of Numerical Aspects in POM and ROMS. Tal Ezer Princeton University (in collaboration with H. Arango (Rutgers) & A. Shchepetkin (UCLA); Supported by ONR). Part of an initiative to develop, evaluate and test an expert Terrain-following Ocean Modeling System (TOMS).

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Comparisons of Numerical Aspects in POM and ROMS

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  1. Comparisons of Numerical Aspects in POM and ROMS Tal Ezer Princeton University (in collaboration with H. Arango (Rutgers) & A. Shchepetkin (UCLA); Supported by ONR)

  2. Part of an initiative to develop, evaluate and test an expert Terrain-following Ocean Modeling System (TOMS) Compare numerical elements and parameterizations in POM and ROMS/TOMS in terms of their numerical errors, numerical stability, computational cost etc. • Time stepping algorithms • Advection schemes • Pressure gradient schemes • Other numerical and configuration aspects

  3. Model attributes- similarities and differences

  4. Model configuration ROMS/TOMS POM

  5. 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

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

  7. 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

  8. Effect of advection scheme on model: Stream function anomaly ADV2- 2nd ord. cnt. ADV4- 4th ord. cnt. ADV3- 3rd ord. upst.

  9. Advection Schemes in ROMS Second Order Centered Third Order Upstream Bias Fourth Order Centered V

  10. Time-stepping schemes(split mode: baroclinic/internal and barotropic/external) * Different terms in 3D ROMS may be treated differently

  11. 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

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

  13. Computational cost for different models & parameterizations

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

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

  16. Sensitivity to bottom topography T=85min T=85s T=111min T=111s

  17. Pressure Gradient Schemes

  18. 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)

  19. PG errors- moderately steep seamount

  20. PG errors- very steep seamount

  21. (preliminary) conclusions • New numerical schemes show promising results in reducing numerical errors while saving computational costs. • However, the behavior of these schemes may be more complicated than standard schemes, and require users for more careful choices of model parameterizations. • Therefore, communication between developers and users is important. • Further developments and testing of more elements for TOMS will continue.

  22. And finally, no matter what car you drive (POM, ROMS, etc.) … … enjoy the ride as much as we enjoy building the car… THANK YOU

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