25 
In general, one often uses the Sum of coldness for describing the winter severity. The so- 
called sum of coldness is the sum of negative daily air temperatures in the period from 1 
November to 31 March. The sum of coldness reaches, for the mild ice winter 1988/89, the 
value 24.9 °C, for the moderate ice winter 1976/77, 77.4 °C, and, for the very strong ice 
winter 1986/87, 327.9 °C (data from German Weather Service, Station Putbus). In the period 
1961-1990, this parameter varied for the station Putbus, situated on the southern coast of 
island Rügen, from 407 °C in the extremely strong ice winter 1962/63 to 11.8 °C in the very 
mild ice winter 1974/75 (Fig. 2.6). 
■ KS for strong ice w inters □ KS for moderate ice w inters □ KS for mild ice w inters 
Winter 
Figure 2.6. Variation of sum of coldness (KS) for different ice winter severity types in the 
period 1961-1990 for the Station Putbus. 
In the strong to very strong ice winters, the sum of coldness reaches values (here for the 
Station Putbus) above 200 °C. For the moderate ice winters, the sum of coldness varies, as a 
rule, between 100 and 200 °C. If the sum of negative daily air temperatures for the whole 
winter does not exceed the value 50, so only small ice production is to be expected. In the 
range between 50 and 100 °C, moderate as well as mild ice winters are evident. Five winters: 
1980/81, 1964/65 1983/84, 1977/78 and 1976/77 have approximately equal sums of coldness, 
but three of them are classified as moderate, and two of them as mild ice winters. Here, 
among other things, the distribution of the negative air temperatures in the winter months is 
very important, as it is shown in the Figure 2.7. 
November Decern ber(1-15) Decern ber(16-31) January February March 
M onth 
Figure 2.7. Distribution of the monthly sum of coldness in moderate ice winters 1964/65, 
1976/77, 1977/78 and in the mild ice winters 1980/81, 1983/84.