i 
Aplìnkos tyrìmaì, inzinerija ìrvadyba, 2007.Nr.3(41), P. 18-24 
Environmental Research, Engineering and Management, 2007. No. 3(41), P. 18-24 
ISSN 1392-1649 
The BSH New Operational Circulation Model Using General 
Vertical Co-ordinates 
Stephan Dick, Eckhard Kleine 
Federal Maritime and Hydrographic Agency, Germany 
(received in April, 2007; accepted in Septeber, 2007) 
At the Federal Maritime and Hydrographic Agency (Bundesamt fur Seeschiffahrt und Hydrographie) 
(BSH), a new model version of a circulation model is under development which will use not only an 
improved grid resolution but also a novel formulation of the vertical co-ordinate. The three-dimensional 
baroclinie circulation model (BSHcmod) is an important component of the operational model system, which 
has been running at the BSH for more than 20 years now. Important applications of the model system are the 
support of the BSH’s water level prediction service, forecasting of oil drift paths and pollutant dispersion, as 
well as water quality studies. 
The circulation model simulates tidal, wind and density driven motion in the entire North Sea and the 
Baltic Sea region. Two nested and interactively coupled grids are used for the German Bight and the western 
Baltic Sea. The horizontal grid spacing of the new version is 900 m in the nested areas, and approx. 5 km in 
the other parts of the North Sea and the Baltic. The vertical grid resolution has been improved as well. In 
addition, a new type of vertical co-ordinate representation has been implemented which allows layer 
thicknesses to be varied in time and space. 
With regard to the performance of general circulation models in a more general context, the new 
formulation provides a dynamic co-moving description of stratification and its maintenance. Internal 
dynamics are captured using weakly inclined flexible co-ordinate surfaces. The formulation is of the 
evolution type, and all common forms of vertical representation are recovered as special examples. 
Key words: circulation model, grid, prediction sendee, vertical co-ordinate 
1. Introduction 
An operational numerical model system 
supporting various maritime services has been in use 
at the BSH for many years now (Dick and Soetje, 
1990, Dick et al., 2001). The model system is an in- 
house development of the BSH. Its main components 
are hydrodynamical models computing currents, 
water levels, temperatures, salinities, and ice cover in 
the North Sea and the Baltic (BSH circulation model, 
BSHcmod) and dispersion models to compute the 
drift and dispersion of substances (Lagrangian and 
Eulerian dispersion models, BSHdmod.L and 
BSHdmod.E). The other components of the model 
system are a surge model (BSHsmod) and local 
models for German estuaries, which were developed 
in order to provide medium-range surge predictions to 
the BSH’s water level prediction service. A new 
version (v4) of the model system is currently being 
developed which incorporates several improvements 
over its predecessor, version 3. The most important 
alterations are an enhanced horizontal and vertical 
grid resolution, the introduction of a new vertical co 
ordinate to the circulation models, and the 
implementation of a coupled circulation and wave 
model with a 3 nm grid spacing in the North Sea and 
the Baltic. (Fig. 1)