hans burchard 1,3 , frank janssen 2 , karsten bolding 3 , lars umlauf 1 , and hannes rennau 1
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Hans Burchard1,3, Frank Janssen2, Karsten Bolding3, Lars Umlauf1, and Hannes
Rennau1
1. Baltic Sea Research Institute Warnemünde2. Bundesamt für Seeschifffahrt und Hydrographie
3. Bolding & Burchard Hydrodynamics
hans.burchard@io-warnemuende.de
Estimates of vertical mixing due to dense bottom currents
in the Western Baltic Sea
Motivation: wind farms in the Western Baltic Sea
Kriegers Flak
Goal: Quantify natural mixing for evaluating additional mixing effects due to offshore constructions. Method: Three-dimensional numerical modelling.
GETM is a 3D numerical model for estuarine,
coastal and shelf sea hydrodynamics with • Coupling to GOTM Turbulence Module• Generalised vertical coordinates• High-resolution advection schemes• Parallel execution•…
GETM Western Baltic Sea hindcast
Model setup:
Meteo: 7 km (DWD)
BC/IC: 3 nm Baltic Seamodel based on MOM-3
Period: Sep 2003-May 2004
Resolution: 0.5 nm
# of layers: 50 GVC
GETM Western Baltic Sea hindcast
GETM Western Baltic Sea hindcast
Western Baltic Sea monitoring stations
Darss Sill: 19 m
+
Drogden Sill: 8 m
+MARNET (IOW/BSH)
Farvandsvæsenet
+
Arkona Buoy: 48 m
Model validation: Darss Sill
Model validation: Drogden Sill
Model validation: Arkona Buoy
Model validation:
Section across
Kriegers Flak
Quantification of vertical mixing
Non-averaged salinity equation:
Reynolds decomposition:
Mean salinity equation
Micro-structure salinity variance equation:
Vertically integrated mean salinity variance:
Vertically integrated salinity variance equation:
Model derived annual mean vertically integrated salinity variance decay in Western Baltic Sea
Vertically integrated turbulent salt flux
Alternative measure for vertical mixing:
Model derived annual mean vertically integrated vertical turbulent salt flux in Western Baltic Sea
Conclusions:
Density currents in Western Baltic Sea are highly variable,
show a complex transverse structure (see Umlauf et al.)
and induce substantial natural transports and mixing.
A suitable model-based quantification of vertical mixing
is given by the
decay of the vertically integrated mean salinity variance.
Next question:
How big is the additional numerically-induced mixing ?
RV Gauss leaving Warnemünde for its last research cruise
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