14
by one 6 m and two 10 m layers. After two 25 m layers, the thickness of the deepest
layer varies between 50 m and 250 m.
As mentioned above, the time step has to fulfil the CFL criterion for the propagation of
long gravity waves. To meet the stability criterion the time step is set to 90 s (10 km grid)
and 45 s (1.8 km grid). The model presently is run on a SUN E1000 using 6 processors.
The computing time for a 72 hours simulation period is approximately 4 hours. In winter it
may be somewhat longer if there is much ice formation.
The circulation model run starts at approx. 9 p.m. when meteorological forecast data
based on the 12 o clock analysis and wave model results have been transmitted from the
DWD to BSH (Fig. 4). The circulation model uses the 12 to 84 h meteorological and
wave forecasts. Circulation model results based on the 12 to 36 h predictions are stored
in the model data archive, while the 36 to 84 h forecast interval is written on hard disk.
These data will be recalculated on the next day using new meteorological predictions.
The daily water level and current forecasts computed by the circulation model are stored
with a temporal resolution of 15 minutes, first on hard disk and later in the BSH’s data
archives. These data - together with wind data - form the basis for dispersion and drift
calculations. All other model results (water temperature, salinity, eddy coefficients and ice
data) are stored with a temporal resolution of 60 minutes.
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Fig. 4; Forecast scheme of BSH's Circulation Model
