Ice  Winter  Severity  in  the  Western  Baltic  Sea  in  the  Period  1301-1500

51

20-year  low-pass  filter  40-year  low-pass  filter

Fig.  7.  Long-term  variations  in  the  ice  winter  index  numerals  in  the  period  1401-1700.

Fig.  8.  Variations  of  the  ice  winter  index  since  1401.
The  variations  of  the  ice  winter  index  for  the  total  period  1401-2005  are  shown  in  Figure  8.  The
solid  curve  represents  the  smoothed  ice  winter  numerals  obtained  by  applying  a  Gaussian  lowpass
  filter  with  a  40-year  cut-off  period.  The  dark  areas  denote  the  period  of  increased  ice
winter  severity  with  regard  to  the  arithmetic  mean  of  0.529  for  the  period  1401-2005  (horizontal
solid  line).  The  standard  deviation  a  =  ±  0.826.  This  diagram  can  be  compared  with  that  for
1501-1995  period  in  Figure  3,  by  Koslowski  and  Glaser,  1999.
The  periods  with  increased  or  reduced  ice  winter  severity  related  to  the  arithmetic  mean  of
0.529  in  the  time  from  1401-2005  have  been  compiled  in  Table  2.  The  results  can  be  partly
compared  to  the  data  in  Table  II  shown  by  Koslowski  and  Glaser,  1999.  The  differences
between  the  time  periods  in  the  two  tables  are  attributable  to  the  changed  mean  value  for  the
total  time  period  and  to  the  inclusion  of  additional  data  for  the  period  prior  to  1520.