Die Kuste, 81 (2014), 255-271 
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2.1 Overview 
The numerical weather forecast models of the German Weather Service (DWD), COS- 
MO-EU (LME) and GME, are at die top level of the applied model chain. LME and 
GME provide the needed atmospheric forcing for both ocean model components on a 
four-times-daily basis with a forecast lead time of up to 7 days. BSElcmod is run with a 
horizontal resolution of about 5 km for the whole North and Baltic Sea area and comes 
with a 2-way nested grid increasing the resolution to about 900 m in the German Bight 
and western Baltic Sea (DICK et al. 2001). A further refinement of grid resolution up to 
90 m has recently been achieved for die sub-region of die Elbe estuary (MULLER- 
Navarra and BORK 2012). Besides die atmospheric forcing, die tidal water level at the 
open boundaries in the North Sea and freshwater inflow from the largest rivers are driv 
ing forces of the circulation model. At present BSElcmod provides a three day forecast of 
water level, current, temperature, salinity and ice coverage once a day in fully automatic 
fashion. The model output is archived with a time step of 15 minutes for water level and 
current and hourly for the other variables together with the atmospheric forcing. The 
model data archive provides the basis for all drift simulations and a range of furdier ap 
plications. 
To forecast die drift of oil, objects and conservative substances a Lagrangian disper 
sion model is used. To date an in-house developed Lagrangian drift model, called BSHd- 
mod.L (DICK and SOETJE 1990) is applied at BSH. BSHdmod.L uses the above men 
tioned archived BSHcmod model fields and wind forecasts of LME. It was one of die 
first Lagrangian dispersion models operationally predicting oil drift and fade in Nordi and 
Baltic Sea and has been very successfully applied in die past e.g. during die Pallas wreck 
age in 1998 or die Baltic Carrier collision in 2001. Later on the model code was shared 
with neighboring Nordi and Baltic Sea countries like Denmark or Sweden, where it de 
veloped in parallel. The Swedish Meteorological and Hydrological Institute (SMHI) and 
the predecessor institution of die Forsvarets Center for Operativ Oceanografi (FCOO) 
used BSHdmodL to upgrade the common HELCOM modelling and drift forecasting 
system for oils and chemicals called SeatrackWeb. They continuously developed die drift 
model core (called Particle Advection and Dispersion Model, PADM), enhanced it with a 
graphical user interface (GLT) and made it accessible via die internet (Ambjorn et al. 
2011 ). 
Several institutes run SeatrackWeb separately and in different versions. For example 
SMHI hosts die official HELCOM site (https://stw-helcom.smlii.se/) and extra produc 
tion sites for special users in Swedish lakes and fjords (Vanern and Brodfjorden) while 
FCOO hosts dieir own version for Danish users. BSH joined die SeatrackWeb developer 
group in 2006 and adapted SeatrackWeb for BSH special requirements for example the 
use of nested grids and an extended model area. Recently SeatrackWeb runs in operation 
al mode using BSHcmod forcing. The BSH version of SeatrackWeb is available under 
http://stw.bsh.de/seatrack . 
Mainly German authorities, including BSH itself, are die users of die BSH version of 
SeatrackWeb, so die target area of die model is die German Bight and die Western Baltic 
Sea witii a 900 m resolution of the water current field (see blue area in Fig.l). Outside this 
area die currents have a resolution of about 5 km in the North-, Baltic Sea and in parts of 
the English Channel.