Turbulent mixing processes in Microtidal Coastal Flows Fluxes and Structuresin Fluids 05

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Turbulent mixing processes in Microtidal Coastal
FlowsFluxes and Structuresin Fluids 05
Philippe Fraunié et al
Laboratoire de Sondages Electromagnétiques de
lEnvironnement Terrestre (Université de Toulon
et du Var)
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Physics

• Coastal flows are basically fully 3D and mainly
  baroclinic
• 3D upwellings / density currents
• Wind forcing relevant scales?
• Baroclinic instability in complex bathymetry
• Density fronts

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I River dischargein Microtidal sea

• River plume dynamics (Garvine )
• - Nutrients inputs (tap)
• - density flows (including fronts, interfaces and
  intenal waves)
• - Region of Fresh Water Influence (Simpson 97)

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Ebro site
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Nested Models (P. Garreau)
Mediterranen model (rank 0)
DX12 km DT1200s
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Upwelling Location
wind
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Rhone river dischargeTypical situation 2001
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Aladin Winds / Mars currents, SSS and SeaWiFS
image
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II. The Rhône river plume
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Rhône site G. Reffray et al
Surface velocity and Salinity
SPOT Image Suspended matter
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Secondary flows.
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3D Flows
5 m depth
Transport
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Direct Simulations
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Factor Analysis
Transport (SW equations) a) upwelling b) plume,
c) background and d) NL interactions
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III. Mixing processes

• High stratification mechanisms
• - Vertical mixing
• - fronts
• - internal waves

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River plume front
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Radar measurements
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VHF Radar Measurement of dynamical stratification
(Broche et al)
(dB)
0 Doppler Frequency(Hz)
U1
Bragg line 25 cm
U2
hydrodynamic line 50 cm
électromagnetic line37.5 cm
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III The layering effect
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Successive infinitesimal perturbation (1)
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Piecewise quadratic rebuilding of a salinity
discontinuity. 1st line initial distribution
but also the piecewise constant rebuilding
(UPWIND scheme). 2nd line PPM scheme without
the traitment for the monotonicity 3rd line
complete PPM scheme (continue line) and QUICKEST
scheme (dots line).

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SAMPOS floating System(JL Devenon)(ADP DL7
GPS)
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Stratification in the Rhône river plume BIODYPAR
field campaign (PNEC, 1999)
salinity
velocity
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CTD and velocity profiles
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Settling velocity
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Active transport (JJ Naudin)
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Conclusion

• Characteristics of stratified coastal flows
• non linear interaction barotropic/baroclinic
  modes
• Secondary flows
• complex turbulent mixing
• Mixing processes
• scalar fields dispersion
• breaking internal waves
• Layering effect
• thermocline
• river plumes