Ice Winter Severity in the Western Baltic Sea in the Period 1301-1500 
55 
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Fig. 12. Variations of mean ice winter severity index during the period 1311-1994 calculated 
from the number of anomalous ice winters per decade for time intervals of 19 years. 
Conclusions 
Ice winter severity in the Western Baltic has been reconstructed for the period 1301-1500 using 
the ice winter index numerals 
The quality of reconstructed data for the period 1301-1500 is rather poor, especially in the first 
half of this period. However, the data series from 1401 to 1500 can be analysed with an 
acceptable error similar to the 1501-2005 time series 
Compared to the 1401-2005 mean, the Gaussian low-pass filtered time series of the ice winter 
index numerals with a 40-year cut-off period shows a higher severity in 1423-1442, 1457-1468, 
and 1499-1517, while periods of lower severity occurred in 1401-1422, 1443-1456, and 1469- 
1498 
The probability of occurrence of anomalous ice winters was investigated for the time period 
1301-1400. A linear relationship between the number of anomalous ice winters per decade and 
the ice winter severity index, found by Koslowski (1999), was used to calculate the value of the 
mean ice winter index for this time period. 
The level of ice winter severity between 1301 and 1400 is continuously below that of the 
reference period 1401-2005 and even slightly lower than that of the 20 th century.