towards dynamically consistent boundary forcing
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Towards Dynamically Consistent Boundary forcing
Jeroen Molemaker (UCLA)Evan Mason (ULPGC)
Sasha Shchepetkin (UCLA)Francois Colat (UCLA)
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One way nesting
• Obvious limitations:– One way will never be two way!
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The round peg and the square hole
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Testing lab: Canary Current system
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Forcing at side boundaries
• Forcing of the outermost grid.– Something ROMS
• Forcing of (off line) one way nested grids– ROMS ROMS
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Forcing the outermost grid
• Output from other (global) models
• Observations (such as World Ocean Atlas)
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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
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Our ‘truth standard’
Drifter data SSH variance
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World Ocean Atlas 2005• Using level of no motion (1300 m)
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World Ocean Atlas + absolute SSH
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World Ocean Atlas + absolute SSH
‘crude’ Ekman layer transport
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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)/
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Roms’ Ekman spiral
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World Ocean Atlas + SSH ‘spiral’ Ekman transport
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Impervious to baroclinic structure?
Patrick style Ekman KPP spiral Ekman
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How well did we do?
Data:
Model:
Drifters SSH variance
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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)
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ROMS ROMS
• Sigma z-levels Sigma coordinate
• No boundary mass flux correction
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Or not so reasonable?
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Horizontal-vertical interpolation
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Matching boundary mass flux with parent grid
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Matching grids at the boundary
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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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