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Modeling Upper Ocean Mixing in DYNAMO: a fish story

Modeling Upper Ocean Mixing in DYNAMO: a fish story. W. Smyth, J. Moum Oregon State University. Testing the model Application to DYNAMO: fish turbulence The upper ocean heat budget. T he Nonlocal K-Profile Parameterization (KPP) (Large et al. 1994). diffusivity profile. processes.

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Modeling Upper Ocean Mixing in DYNAMO: a fish story

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  1. Modeling Upper Ocean Mixing in DYNAMO: a fish story W. Smyth, J. Moum Oregon State University Testing the model Application to DYNAMO: fish turbulence The upper ocean heat budget

  2. The Nonlocal K-Profile Parameterization (KPP)(Large et al. 1994) diffusivity profile processes surface fluxes Langmuir, convection (nonlocal) Surface-driven data assimilation boundary layer base shear instability Ri-dependent IGW breaking uniform

  3. 1. Testing the KPP: two cases La Nina El Nino The plan: Assimilate observed U, V, T, S into 1d upper ocean model. Infer turbulence parameters from model Compare with in situ microstructure measurements

  4. La Nina 2008, 0N, 140WDissipation rate comparison: GOOD OBS MODEL mean within 10%

  5. El Nino 1990-91, 0N, 140WDissipation rate comparison POOR too weak too strong mean dissipation rate 30% high

  6. Time-mean vertical heat flux El Nino OBS La Nina model OBS model PWP 1000W/m2! La Nina: mean good, vertical structure …? El Nino: overpredicts (weak) mixing

  7. Application to DYNAMO leg 3:the mysterious mixing at 60m. >100W/m2 ! missing from model all mechanical sources ruled out WWB1 WWB2

  8. Could fish make the mystery mixing? echosounder profiler YES!

  9. Composite diurnal cycle of dissipation rate and acoustic scattering (fish)

  10. Parameterizing fish turbulence scatter! Problem: order-of-magnitude scatter.

  11. Is turbulence at the ML base affected by fish?Maybe KPP can tell us. Comparison of KPP/OBS heat flux at the ML base WWB2 WWB1 No systematic bias 

  12. Conclusions • KPP works well in La Nina (strong, interior-driven mixing) • KPP overpredicts mixing in El Nino (weak, surface-driven) • Fish can make a lot of turbulence. • KPP is useful for distinguishing fish/mechanical turbulence • Turbulent flux at the mixed layer base is all mechanical.

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