Die Kuste, 81 (2014), 273-290 
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area. As part of this cooperation the model code developed at BSH — called BSHcmod — 
was spread in die Baltic Sea community. One branch (HIROMB) was installed and fur 
ther developed at the Swedish Meteorological and Hydrological Institute (SMHI) and is 
until today die basis for die official HELCOM oil spill response system in die Baltic. 
Another branch started a few years later at Danish Meteorological Institute (DMI) where 
it founded the Danish storm surge warning system. All tiiree model lines where actively 
development over several years and somehow diverged over time. During recent years 
and witii support of die MyOcean projects an effort was made to merge die tiiree devel 
opment lines into one. The outcome of tiiis effort is die HIROMB-BOOS-Model (HBM) 
nowadays jointly development by BSH, DMI, the Finnish Meteorological Institute (FMI) 
and the Marine Systems Intitute at Tallinn University (MSI). At BSH die transition from 
the current operational model code BSHcmod towards HBM is not yet fully completed, 
so tiiis publication, in which for the first time results from the future operational model 
HBM are presented, describes partly work in progress and mostly results from die ongo 
ing calibration phase. 
2 Model system 
2.1 Equations 
The equations of die physical kernel of HBM are mostly die same as tiiose of BSHcmod 
which are described in DICK et al. 2001 and DICK et al. 2008. An important difference to 
the BSHcmod versions is die possibility to choose between dynamical vertical co 
ordinates (Kleine 2004) and z-co-ordinates with a free surface by a compiler flag. For 
operational use at BSH dynamical vertical co-ordinates are chosen. 
Changes witii die largest impact on die physical kernel (in comparison to the latest 
BSHcmod version 4) are the implementation of a new turbulence scheme — now a 
k-omega model is used, which is described in Berg 2012 — and die grid nesting. In HBM 
a fully dynamical two-way nesting is implemented. Tiiis means tiiat die nested grid is a 
continuation of the grid into which it is nested. Therefore, areas which are covered by 
more than one grid witiiin one setup are just calculated in one - the finest - grid. In all 
coarser grids the finer grid area is non-active. In the BSH NOKU-setup (see Fig 2) tiiis is 
realized in die inner German Bight and die Western Baltic, where only die so-called 
KU-grid (the fine grid) is active, whereas the corresponding points in so-called NO-grid 
(die coarse grid) are non-active (grey area in the NO-grid shown in Fig. 2). However, the 
products from NO-grid still cover die whole area. A more detailed description of die 
nesting equations and a very detailed description of die technical implementation witii a 
focus on parallelization in HBM can be found in Berg and POULSEN 2012. 
Furdiermore some parameterizations were adjusted whereby especially die wind stress 
parameterization is noteworthy, because in contrast to BSHcmod-versions which use a 
linear approach, a quadratic approach for calculating the wind drag coefficient is chosen. 
2.2 Setups / bathymetry 
The BSH model system consists of four model grids which are calculated in tiiree differ 
ent setups. The first setup of die model chain is a 2D-model of die Nordi East Atlantic