hans burchard baltic sea research institute warnemünde, germany hans.burchard@io-warnemuende.de...

Hans Burchard

Baltic Sea Research Institute Warnemünde, Germany

hans.burchard@io-warnemuende.de

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

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

GOTM is a water column model with modules for state-of-the-art turbulence closure models biogeochemical models of various complexities

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• …

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.

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).

GETM-GOTM-Bio coupling example: ERSEM simulation for North Sea(Simulation and animation by Piet Ruardij, NIOZ, The Netherlands)

Western Baltic Sea Study

Kriegers Flak

Motivation: wind farms in the Western Baltic Sea

Western Baltic Sea monitoring stations

Darss Sill: 19 m

+

Drogden Sill: 8 m

+MARNET (IOW/BSH)

Farvandsvæsenet

baroclinic barotropic

Inflows over Drogden Sill

surface

bottom

Source: Farvandsvæsenet

Where does the Sound plume go ?

?

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

Plume passing Kriegers Flak (Feb 2004)

GETM Western Baltic Sea hindcast

GETM Western Baltic Sea hindcast

GETM Western Baltic Sea hindcast

Model validation: Darss Sill

Model derived annual mean mixing in Western Baltic Sea

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 ?

GETM 2DV Slice Model: Transverse gravity current structure

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.

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

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.

Salinity difference HW-LW

Temperature difference HW-LW

Density difference HW-LW

Hypothesis: This must have a dynamic impact on tidal flow and SPM transport, see the theory of Jay and Musiak (1994) below.

Testing with GOTM supports hypothesis:

Residualonshorenear-bedcurrent

Along-tidesalinity gradientprescribed

Bottom-surface salinity

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.

The Sylt-Rømø bight

Bottom salinity at high and low water during periodically steady state.

Vertically averaged current velocity during full flood and full ebb.

Cross-sectionaldynamics

Total water volume and SPM unit mass in budget boxes

Case with density differences, tidal periods # 46-55

Total excess SPM mass in budget boxes

Case with density differences, tidal periods # 46-55

Total water volume and SPM unit mass in budget boxes

Case with no density differences, tidal periods # 46-55

Total excess SPM mass in budget boxes

Case with no density differences, tidal periods # 46-55

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.

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.