hartmut peters’ projects: miwe – m editerranean outflow i nternal w ave e xperiment nsf (no...
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Hartmut Peters’ Projects:
• MIWE – Mediterranean Outflow Internal Wave Experiment
NSF (no funding left)
with Jonathan Nash, OSU, Josep Pelegrí, Barcelona, Spain
• Development of a Two-Equation Turbulence Model for Mean Shear-
and Internal Wave-Driven Mixing
ONR / ONR Global
with Helmut Baumert, IAMARIS, Hamburg, Germany
Common fluid dynamics underpinning:
Stratified flows support both turbulence and internal gravity waves.
“MIWE” - The Mediterranean Outflow Internal Waves ExperimentPIs: Jonathan Nash (OSU), H.P. (ESR), Josep Pelegrí (Marine Sciences, Barcelona)
Funded by NSF and Spanish agencies
Internal Waves and Hydraulics in the Med Outflow Hartmut Peters
Earth and Space Research, SeattleJonathan Nash and Bill Smyth
OSU
Instrumentation
• Two moorings, at and downstream of sill
• Lowered ADCP / CTD in repeated
• streamwise and spanwise transects,
• tidal variations resolved,
• u,v,T,S,
• turbulence from overturning scales.
R/V García del Cid
Flip the Equatorial
Undercurrent
upside-down→
the situations
in overflows
Our (original) hypothesis [modified]:Internal wave-driven momentum fluxesare part of the outflow momentum balance.
Mean along-stream fluctuations: APE and
Downstream of sill:- Tenfold increase in available potential energy < N2 2 >- Hundredfold increase in turbulent dissipation rate
- APE and small above overflow
Downstream & upstreamvelocity and temperaturespectra
Downstream has high-frequencypeak with high variance in T and Vat ~5-12 cph N.
Upstream has much less horizontalkinetic energy than downstream.
Vertical momentum flux
We can estimate thecontamination(i) of u’ and v’ due tow’ and instrument tilt and,(ii) at least in part, bymooring motion.
(i) is demonstrated inthe graph by the dashedlines for tilts of 0°-30°.
(ii) O(10-20%)…
Vertical momentum flux:- O(1 pa) upward – large! –- quantitatively uncertain- qualitatively robust
Development of a Two-Equation Turbulence Model for Mean Shear- and Internal Wave-Driven Mixing
-- Nothing to report (yet) –
• Theory / modeling• Long-term collaboration, previous publications - series of closure
models which build upon each other, few or no adjustable
parameters, increasing explicit acknowledgment of internal waves• Adressing the “birth defect” of conventional turbulence closure:
Reynolds decomposition into “mean” and turbulence.• Verification through direct 1:1 comparison with oceanic/estuarine
turbulence observations
Current state:
(A) Closure that can reproduce energetuc, shear-driven turbulence for Ri<1/4 well – but fails for weak turbulence at Ri>>1/4 in the pycnocline – where mixing presumably is driven by internal waves.
Current state:
(B) We have a closure that accounts for the two limits of shear-driven mixing without internal waves and wave-driven mixing with zero mean shear.This model reproduces the wave-turbulence transition of D’Asaro and Lien.
Our task: allow mean shear and waves simultaneously.
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