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Towards Dynamically Consistent Boundary forcing

Towards Dynamically Consistent Boundary forcing. Jeroen Molemaker (UCLA) Evan Mason (ULPGC) Sasha Shchepetkin (UCLA) Francois Colat (UCLA). One way nesting. Obvious limitations: One way will never be two way!. The round peg and the square hole. Testing lab: Canary Current system.

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Towards Dynamically Consistent Boundary forcing

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  1. Towards Dynamically Consistent Boundary forcing Jeroen Molemaker (UCLA) Evan Mason (ULPGC) Sasha Shchepetkin (UCLA) Francois Colat (UCLA)

  2. One way nesting • Obvious limitations: • One way will never be two way!

  3. The round peg and the square hole

  4. Testing lab: Canary Current system

  5. Forcing at side boundaries • Forcing of the outermost grid. • Something  ROMS • Forcing of (off line) one way nested grids • ROMS  ROMS

  6. Forcing the outermost grid • Output from other (global) models • Observations (such as World Ocean Atlas)

  7. Observation based forcing • World Ocean Atlas 2005 T, S monthly climatology • Absolute SSH (Rio, 2005) • Now, annual mean, but we should include at least monthly averaged perturbations

  8. Our ‘truth standard’ Drifter data SSH variance

  9. World Ocean Atlas 2005 • Using level of no motion (1300 m)

  10. World Ocean Atlas + absolute SSH

  11. World Ocean Atlas + absolute SSH ‘crude’ Ekman layer transport

  12. Assessing large scale, slow dynamics • Subtract geostrophic flow • - Scale vertical profiles with mixed layer depth, f and wind stress vector: • z’ = z/Hbl, (u’) = (u Hbl f)/t

  13. Roms’ Ekman spiral

  14. World Ocean Atlas + SSH ‘spiral’ Ekman transport

  15. Impervious to baroclinic structure? KPP spiral Ekman Patrick style Ekman

  16. How well did we do? Data: Model: SSH variance Drifters

  17. ROMS  ROMS • Expected consistency much higher • Only regime transition is unavoidable • Starting point: • Methods as existing in ROMS tools (Pierrick Penven, Patrick Marchesiello…. Many others)

  18. ROMS  ROMS • Sigma  z-levels  Sigma coordinate • No boundary mass flux correction

  19. Or not so reasonable?

  20. Horizontal-vertical interpolation

  21. Matching boundary mass flux with parent grid

  22. Matching grids at the boundary

  23. Summary • One way nesting can be good when: • Solutions have consistent dynamics • roms  roms • No enormous jumps in resolution • Interpolation does not destroy said consistency

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