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.