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Hans Burchard
Baltic Sea Research Institute Warnemünde, Germany
[email protected]
Collaboration: Lars Arneborg, Thomas Badewien, Karsten Bolding, Jorn Bruggeman, Volker Fiekas,
Götz Flöser, Hans Ulrich Lass, Volker Mohrholz, Rolf Riethmüller, Piet Ruardij, Joanna Staneva,
Lars Umlauf
Applications of the General Estuarine Transport Model (GETM)
for coastal ocean process studies
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Program today
Tools:
General Ocean Turbulence Model,
www.GOTM.net
General Estuarine Transport Model, www.GETM.eu
Applications:
Western Baltic Sea – dense bottom currents
Wadden Sea – suspended matter accumulation
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GOTM is a water column model with modules for state-of-the-art turbulence closure models biogeochemical models of various complexities
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GETM is a 3D numerical model for estuarine,coastal and shelf sea hydrodynamics with applications to the
• Tidal Elbe • Wadden Sea• Limfjord• Lake of Geneva, • Western Baltic Sea,• North Sea – Baltic Sea system• …
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Present GETM characteristics ... physics ...
Solves three-dimensional primitive equations withhydrostatic and Boussinesq approximations.
Based on general vertical coordinates.
Options for Cartesian, spherical and curvilinear coordinates.
Fully baroclinic with tracer equations for salinity, temperature,suspended matter and ecosystem (from GOTM bio module).
Two-equation turbulence closure models with algebraicsecond-moment closures (from GOTM turbulence module).
Wetting and drying of intertidal flats is supported also inbaroclinic mode.
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Present GETM characteristics ... numerics ...
Consistent explicit mode splitting into barotropic and baroclinic mode.
High-order positive-definite TVD advection schemes withdirectional split.
Choice of different schemes for internal pressure gradientcalculation.
Consistent treatment of zero-velocity bottom boundary condition for momentum.
Positive-definite conservative schemes for ecosystem processes (in GOTM-Bio module).
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GETM-GOTM-Bio coupling example: ERSEM simulation for North Sea(Simulation and animation by Piet Ruardij, NIOZ, The Netherlands)
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Western Baltic Sea Study
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Kriegers Flak
Motivation: wind farms in the Western Baltic Sea
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Western Baltic Sea monitoring stations
Darss Sill: 19 m
+
Drogden Sill: 8 m
+MARNET (IOW/BSH)
Farvandsvæsenet
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baroclinic barotropic
Inflows over Drogden Sill
surface
bottom
Source: Farvandsvæsenet
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Where does the Sound plume go ?
?
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5 days
15 days
31 days
Sound lock-exchange experiment with GETM
Main plume goes via northof Kriegers Flak: Is this real ?
Bottom salinity: 8 – 25 psu
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Plume passing Kriegers Flak (Feb 2004)
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GETM Western Baltic Sea hindcast
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GETM Western Baltic Sea hindcast
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GETM Western Baltic Sea hindcast
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Model validation: Darss Sill
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Model derived annual mean mixing in Western Baltic Sea
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Nov 2005: Velocity structure of dense bottom current
Ship A:TL-ADCP
Ship B: Microstructure
View
1 km
Flow
Eastcomp.
Northcomp.
Can we explain the flow structure ?
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GETM 2DV Slice Model: Transverse gravity current structure
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Western Baltic Sea conclusions:
Density currents in Western Baltic Sea are highly variable,
show a complex transverse structure
and induce substantial natural transports and mixing.
For evaluating additional anthropogenic mixing due to
offshore structures on these currents,
proper parameterisations need to be found
and inserted into 3D model (QuantAS-Off).
Multiple bridges and wind farms may result in
cumulative mixing effects.
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Suspended matter
concentrations
are substantially
increased in the
Wadden Sea of the
German Bight.
Total suspended matter from MERIS/ENVISAT on August, 12, 2003.
Wadden Sea study
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The areal view shows
locations of five automatic
monitoring poles in the
Wadden Sea of the
German Bight, operated by
GKSS and the University
of Oldenburg. They record
several parameters in the
water column, such as
temperature and salinity.
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Salinity difference HW-LW
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Temperature difference HW-LW
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Density difference HW-LW
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Hypothesis: This must have a dynamic impact on tidal flow and SPM transport, see the theory of Jay and Musiak (1994) below.
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Testing with GOTM supports hypothesis:
Residualonshorenear-bedcurrent
Along-tidesalinity gradientprescribed
Bottom-surface salinity
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3D simulations with GETM for the Sylt-Rømø bight
Approach:
Simulating a closed Wadden Sea basin (Sylt-Rømø bight)
with small freshwater-runoff and net precipitation.
Spin up model with variable and with constant density
until periodic steady state.
Then initialise both scenarios with const. SPM concentration.
Quantify SPM content of fixed budget boxes.
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The Sylt-Rømø bight
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Bottom salinity at high and low water during periodically steady state.
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Vertically averaged current velocity during full flood and full ebb.
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Cross-sectionaldynamics
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Total water volume and SPM unit mass in budget boxes
Case with density differences, tidal periods # 46-55
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Total excess SPM mass in budget boxes
Case with density differences, tidal periods # 46-55
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Total water volume and SPM unit mass in budget boxes
Case with no density differences, tidal periods # 46-55
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Total excess SPM mass in budget boxes
Case with no density differences, tidal periods # 46-55
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Wadden Sea conclusions:
The hypothesis is strongly supported.
Other mechanisms than density differences
which are also reproduced by the model system
(such as settling lag and barotropic tidal asymmetries)
do not play a major role in this scenario.
Now, targeted field studied are needed
for further confirming the hypothesis.
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RV Gauss leaving Warnemünde for its last research cruise
General conclusion:
Sufficient knowledge about coastal processes is a prerequisite for assessing regional consequences of climate and anthropogenically induced change.