Towards Dynamically Consistent Boundary forcing

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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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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 Presentation

Transcript of Towards Dynamically Consistent Boundary forcing

Page 1: Towards Dynamically Consistent Boundary forcing

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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