30

To  analyse  the  empirical  relationship  between  ice  thickness  and  the  sum  of  coldness  in  the
Szczecin  Lagoon,  approximately  500  measurements  of  ice  thickness  made  by  the  ice
observers  in  Kamin,  Kamminke  and  Ueckermiinde  in  the  winters  1961-1990  were  interpreted.
The  freezing  process  in  waters  like  Szczecin  Lagoon  is  determined  primarily  by  the  air
temperature,  other  factors  (water  temperature,  wind,  snow)  modifying  this  process  to  some
extent.  This  fact  is  clearly  evident  in  Figure  3.1  where  the  maximum  ice  thickness  -  i.e.  the
mean  value  of  maximum  ice  thickness  data  measured  at  the  three  German  coastal  observation
stations  Ueckermiinde,  Kamminke  and  Kamin  in  the  winters  from  1961  to  1990  -  is  shown  in
dependence  on  the  sum  of  coldness  representative  of  this  region.

60
50

O
40  <D

o
7?
3°  =
Cfl
0)
5'
20  o
3

10
0

Winter
Figure  3.1.  Mean  maximum  ice  thickness  and  measured  sum  of  coldness  (station
Ueckermiinde)  in  Szczecin  Lagoon  in  1961  -  1990

It  was  found  that  the  equation  h max  =  2.12*  K s  1/2  -  5.36  well  describes  (R 2  =  0.85,  R  -
correlation  coefficient)  the  variation  of  maximum  ice  thickness  in  the  Szczecin  Lagoon  in
dependence  on  the  sum  of  coldness  (Figure  3.2.).  The  dispersion  of  the  measured  data  is
mainly  attributable  to  subjectivity  of  observations,  local  features  of  different  observation
stations,  and  variability  in  the  occurrence  of  negative  air  temperatures  (distribution  of  the
monthly  sum  of  coldness)  in  winter.  In  Figure  3.3,  the  mean  maximum  ice  thickness
measured  in  Ueckermiinde,  Kamin  and  Kamminke  in  the  ice  winters  of  1990/91,  1991/92,
1992/93,  1993/94,  1994/95,  1995/96,  1996/97,  1997/98  and  1998/99  are  shown  in
dependence  on  the  sums  of  coldness  reached  in  those  years.  Most  ice  thickness  measurements
can  be  represented  with  adequate  precision  by  the  empirically  founded  curve.
Of  higher  practical  interest  is  the  possibility  of  forecasting  ice  growth  during  the  ice  season.  A
reliable  forecast  of  air  temperatures  can  be  given  for  five  to  seven  days  at  best.  Therefore,  we
use  the  following  equations,  derived  empirically  for  the  area  of  Szczecin  Lagoon  and  based
on  the  data  from  the  first  ice  formation  to  the  first  interruption  of  the  ice  growth  process: