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In the Baltic, water level variations are caused mainly by wind effects and seiches, while 
tidal signals are hardly discernible. Water level predictions for the Baltic differ markedly 
from North Sea predictions, which are dominated by the tides and related modelling 
deficiencies. In the western Baltic, the circulation model’s error of predicted water levels 
is much smaller than in the German Bight. 
Figure 8 shows a time series of measured and predicted water levels in the winter of 
1999/2000 at the German Baltic Sea station Warnemünde'. It clearly reflects the strong 
water level changes which are typical of the winter season. Water levels in the first half of 
December varied between -170 and +80 cm. The results of the model agree quite well 
with the measurements, only the mean level of measured and modelled data differs by 
about 20 cm. When comparing the data, the non-coincidence of reference levels should 
be noted. The model data refer to a geopotential surface across the entire domain, while 
the observations do not. The reference level of the observations appears to be elevated. 
A large part of the bias may be attributable to the steric effect (due to an appreciable 
difference in salinity) which is responsible for lifting the mean sea level at Warnemünde 
by about 20 cm as compared to North Sea MSL. However, in the daily water level 
prediction service the shift of the zero levels can be easily corrected by adding a constant 
value. 
Station: Warnemünde 
Fig. 8 Measured and predicted water levels in winter 1999/2000 at the Station 
Warnemünde in the Western Baltic Sea