Baltic Sea Ice Climate Workshop 2005 
26 
Fig. 2. The relationship between the mean winter season air temperature and maximum of 
ice thickness in Virpiniemi (1988-2003) 
The ice thickness compared to the frequential distribution of the temperature 
The analysis of the relationship between the winter mean air temperature and the maximum ice 
thickness gives some explanations to the exceptions. Some winters follow the hypothesis: more 
the temperature is low more the ice cover is large. 
The winter 2002/03 confirms this hypothesis. The Virpiniemi ice thickness got larger and larger 
until March (80 cm). The high winter mean air temperature can be explained because the 
months from October to January were very cold (Fig. 3) even if March was one the warmest 
month of March of the 50 last years. 
The winters 1988/89 and 1991/92 got mean temperatures near -30, but the maximum ice 
thickness, in March for both, evaluated differently, respectively 77 cm and 42 cm. The 
harshness of the winter and the weakness of snow precipitations are the reasons of an 
important thickness of the ice cover in 1988/89. The winter 1991/92 belongs to the 25% of 
warmest winters of the second part of the XXe century (Fig.3). The insulating effect of snow 
(Flaapala, Lepparanta 1997) has also some consequences on ice layers. In 1999/2000, the 
thickness of ice cover was low compared to the temperatures because of the importance of the 
snow cover, about 35 cm. The winter 1996/97 was cold, but the ice thickness was only 67 cm 
and the snow cover was almost nonexistent. Thus, other reasons than the temperature and the 
snow cover could be explained the state of the ice thickness.