The BSH New Operational Circulation Model Using General Vertical Co-ordinates 
19 
Operational Models of BSH (and DWD) 
Meteorological Models 
(GME + LME) of 
German Weather Service (DWD) 
forecasts up to 84 hours 
Wave Models (WAM) 
of German Weather 
Service (DWD) 
forecasts up to 84 hrs 
I wave data 
wind, air pressure, air temperature, 
cloud coverage, specific humidity 
Circulation Model (BSHcmod) 
for North Sea and Baltic Sea 
( 3dim„ 5km + 900m grid) 
Circulation + Wave Model 
(BSHcmod.w) 
for North Sea and Baltic Sea 
( 3dim., 5km) 
T 
Model data archive: currents, water levels, 
eddy coefficients, salinity, temperature, ice data, wave data 
Other forcing: 
tidal predictions, external 
surges (NE Atlantic Model), 
river input (BfG), solar 
radiation 
Surge Model (BSHsmod) 
for North Sea 
(2dim„ 5km, barotropic) 
surge data 
1 
1 1 
Local Circulation 
Models 
Lagrangian Drift and 
Eulerian Dispersion Model 
for estuaries 
Dispersion Model 
(BSHdmod.E) 
(Elbe, Weser, Ems) 
(BSHdmod.L) 
for conservative substances 
for oil, drifting objects and 
and suspended matter 
conservative substances 
Fig. 1. The BSH’s model system driven by models of the German Weather Sendee (DWD) 
2. The Circulation Model 
The circulation models of the North Sea and the 
Baltic are three-dimensional and take into account 
meteorological conditions, tides, and external surges 
entering the North Sea from the Atlantic as well as 
river runoff from the major rivers. Predictions for up 
to 84 hours are computed in daily routine runs, using 
meteorological and wave forecasts supplied by the 
German Weather Service (DWD). Tidal forcing is 
calculated from the harmonic constants of 14 tidal 
constituents. External surges entering the North Sea 
are computed by a model of the Northeast Atlantic 
and are superimposed on tidal forcing. The new 
version of the two-dimensional NE Atlantic model 
has a grid spacing of about 10 km and is also forced 
by meteorological data provided by DWD. 
The circulation model simulates density driven 
(baroclinie) currents, which are of major importance 
in the Baltic Sea. Current freshwater input data of the 
most important rivers are provided by the Swedish 
Meteorological and Hydrological Institute (SMHI) 
and the Federal Institute of Hydrology (BfG) in 
Germany. Heat exchange between the air and water is 
computed by means of bulk formulae using DWD 
forecast data. To simulate temperature and salinity 
advection, the model uses a conservative, shape 
preserving numerical scheme of low numerical 
diffusion (Kleine, 1993). As hydrodynamics is also 
influenced by ice conditions in the North Sea and the 
Baltic, an ice model has been integrated to simulate 
the formation, melting, and drift of sea ice. 
In the BSH’s North Sea and the Baltic Sea 
model, the hydrodynamic parameters are computed on 
two nested and interactively coupled grid nets. Grid 
spacing in the new model version 4 has been reduced 
to approx. 900 m in the German Bight and the western 
Baltic Sea, and approx. 5 km in the other areas of the 
North Sea and the Baltic Sea. Even bigger changes 
have been made to the vertical grid structure as 
compared to the former version. Version 4 not only 
has a larger number of layers and a higher vertical 
resolution but also incorporates a new co-ordinate 
system with weakly inclined flexible co-ordinate 
surfaces. A detailed description of the improved 
model will be provided in the following sections.