Ice Winter Severity in the Western Baltic Sea in the Period 1301-1500 
53 
20-year low-pass filter 40-year low-pass filter 
1301 1401 1501 1601 1701 1801 1901 2001 
Fig. 9. Frequency of occurrence of normal (0) and anomalous (1) ice winters in the period 
1301-2005 
In the publication of Koslowski and Glaser (1999), the best relationship between the number of 
anomalous ice winters and the ice winter severity index was found for 19-year periods in the 
time from 1501-1994 and is linear, see Figure 10. 
Fig. 10. Regression line for the mean ice winter severity index and number of anomalous ice 
winters per decade calculated for time intervals of 19 years for the period 1501-1994 (26 cases) 
Five cases in the period 1401-1500 are in very good agreement with the linear dependence in 
the period 1501-1994, Figure 11.