Baltic Sea Ice Climate Workshop 2005 
54 
• 1501-1994 ♦ 1406-1500 Linear (1501-1994) 
Anomalous Ice Winters per Decade 
Fig. 11. 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) 
and 5 other cases from the period 1406-1500. 
The mean ice winter severity index for the 19-year time interval in the period 1301-1400 can be 
derived from the linear relationship found above. The results are shown in Table 3. 
Table 3. Number of anomalous ice winters and calculated mean ice winter severity index for 
19-year time intervals in the period 1301-1400. 
Time interval 
of 19 years 
Number of 
anomalous 
ice winters 
Number of 
anomalous 
ice winters pro 
decade 
(x) 
Mean ice winter 
severity 
index (y): 
y = 0.1554X + 0.1556 
1311-1329 
4 
2.11 
0.48 
1330-1348 
1 
0.53 
0.24 
1349-1367 
2 
1.05 
0.32 
1368-1386 
0 
0.00 
0.15 
1387-1405 
4 
2.11 
0.48 
Finally, in Figure 12, the variation of the mean ice winter severity index is shown during the 
period 1311-1994. The horizontal solid line represents the arithmetic mean of 0.529 for the 
period 1401-2005. The areas above this line denote phases with an increased ice winter 
severity and are comparable to those obtained for the period 1401-2005 as shown in Figure 8.