Influence  of  the  Temperature  on  Ice  Conditions  in  the  Bay  of  Bothnia  (Baltic  Sea)

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Data  series  of  temperature  and  ice  thickness  were  fixed  for  the  period  1988-2003.  The  main
annual  air  temperature  of  each  year  of  this  period  are  from  the  meteorological  station  of  Oulu
airport.  The  observation  spots  were  almost  at  the  same  place  until  1995,  and  there  was  a
relocation  of  them  after  that.  Some  homogeneity  tests  of  the  climatic  series  were  realised  by
the  FMI  (Finnish  Meteorological  Institute).  The  monthly  variability  of  the  mean  air  temperature  is
important  for  this  study.  The  most  important  variations  of  the  temperature  take  place  during  the
heart  of  the  winter.  It  especially  concerns  the  months  of  December,  January  and  February  (Fig.
1)-A
  succession  of  cold  and  warm  winters  can  be  noticed.  Could  it  be  possible  to  conclude  to  a
significant  trend?  The  mean  air  temperature  of  January  2003  was  the  coldest  one  recorded  for
the  period  1988-2003,  but  January  2003  does  not  belong  to  the  coldest  winters  of  the  end  of
the  XXe  century.
Temperature  data  can  be  in  relation  with  ice  data.  The  ice  thickness  data  series  presents
measurements  made  for  the  period  1988-2003  by  researchers  from  the  station  of  Virpiniemi.
The  analysis  of  a  statistic  relation  between  two  quantitative  variables  -  temperature  and  ice
thickness  -  is  for  validating  or  not  the  hypothesis  mentioned  before.  So  the  intensity  of  the
relation  of  two  variables  can  be  measured  by  a  correlation  coefficient.
Results
The  intensity  of  the  relation  temperature  /  ice  thickness
In  the  Oulu  region,  the  maximum  annual  thickness  of  ice  is  40  to  90  centimetres,  and  the  winter
mean  air  temperatures  is  -3  to  -7.50  from  1988  to  2003.  The  relationship  between  the  winter
air  temperature  and  the  Virpiniemi  annual  maximum  ice  thickness  is  shown  for  the  period  1988-2003
  in  Figure  2.  The  Bravais-Pearson  coefficient  (r)  is  0,607  and  shows  a  good  correlation
between  the  winter  mean  temperature  and  the  maximum  annual  ice  thickness.  Nevertheless
some  winters  are  some  exceptions.  For  instance,  the  winter  1988/89  was  warm,  the  mean  air
temperature  (December  1998  -  April  1989)  about  -30,  but  the  maximum  ice  thickness  was
large,  77  cm.