hartmut peters’ projects: miwe – m editerranean outflow i nternal w ave e xperiment nsf (no...

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.