31 
h = 0.28* K s - 0.29 
valid for mild ice winters, 
Fig. 3.4; 
h = -0.006*Ks + 3.17* K s 1/2 - 6.99 
for moderate ice winters, 
Fig. 3.5; 
h = 0.02* Ks 3/2 - 0.33* K s + 3.97* K s m - 5.96 
for strong ice winters, 
Fig. 3.6; 
h = -0.005* K s 3/2 + 0.12* K s + 1.70* K s 1/2 - 2.94 
valid for all ice winters, 
Fig. 3.7. 
In mild ice winters, the ice thickness in Szczecin Lagoon reaches approximately 10 to 15 cm 
and its growth is described at best by the linear curve (Figure3.4), not by the commonly used 
method in which ice thickness is assumed to be proportional to the square root of the 
accumulated freezing degree days. This result confirms the theoretical treatment of this 
problem by G.D.Ashton [Ashton, 1989]. Taking into account the thermal resistance between 
the top of the ice and the atmosphere, he showed that the newly formed thin ice (up to 10 cm) 
growths linearly with time and air temperature, while for larger thicknesses a transition to the 
T 1/2 growth takes place. As a matter of fact, the ice growth in moderate ice winters (up to 35 
cm) and in strong ice winters (up to 45 cm) in Szczecin Lagoon is described by "square root 
of freezing degree days" law at best (Figures 3.5 and 3.6). To evaluate the practical quality of 
the empirical equations, the ice thickness values measured at the three observations 
stations Kamin, Kamminke and Ueckermiinde during the mild ice winter of 1997/98, the 
moderate ice winter of 1996/97, and the strong ice winter of 1995/96 are marked in the 
Figures 3.4, 3.5 and 3.6. 
At the beginning of the ice season it is not known to which class of severity the ice winter will 
belong and which equation should be used to calculate the ice thickness. The equation valid 
for all winter types is shown in the Figure 3.7. 
Another important forecast is the date of first freezing of particular water areas. The sum of 
coldness needed for the first ice formation to occur in Szczecin Lagoon ranges from 3° to 
20°C in different winters. One of several factors influencing this process is the water 
temperature existing at the time the air temperature drops below 0°C. An attempt to estimate 
the dependence of first ice formation on the water and air temperature in Szczecin Lagoon is 
shown in Figure 3.8. The available data, especially water temperature data, are difficult to 
find, and, unfortunately, they are of poor quality. Nevertheless, the linear dependence of the 
sum of coldness, needed to predict first ice formation, on the water temperature at T air = 0°C 
is clearly discernible. 
K 5 = 2.13+ 3.96% 
It has not been possible so far to test the validity of the equation found because measured 
surface water temperature data from the German coast of Szczecin Lagoon have not been 
available since 1990. An improvement of this method will probably be possible if a good data 
set (may be from the Polish coast) becomes available. 
The empirical equations found allow us to calculate the ice thickness in Szczecin Lagoon in a 
relatively fast and simple way on the basis of air temperature forecasts for the next five to 
seven days during the ice season. If required, such investigation can also be made for other 
water areas along the German coast, but the equations will be more complicated because of 
the larger influence of water depth, salinity, wind conditions and water exchange processes, 
especially in the open sea areas.