Classification of Ice Winters

3 Sea of Bothnia The southern half of the offshore area of the Sea of Bothnia remains ice-free in mild winters (about 34% of winters in the considered range) except for a very narrow strip of ice off the Swedish coastal fast ice and a wide belt of ice off the Finnish archipelagos. In all other winters, drift ice increasing in density toward the north is to be expected throughout the offshore waters. In severe winter seasons (about 16% of winters), the compact drift ice in the entire sea area freezes together, in normal winters only in the northern third. 

4 Bay of Bothnia and the Quark Ice conditions in the Bay of Bothnia are very unfavorable because of its northern location and the largely continental climate. The Bay of Bothnia freezes over regularly each winter, and ice may be present during 7 months of the year. 

In the offshore areas, initial ice normally forms in December, at the northern periphery in the first decade, and at the southern periphery in the third decade. The coastal area of the Bay of Bothnia is normally ice-free again by the second decade of May. After a severe winter, the ice lasts until the first decade of June almost in the entire area. On average, 130-180 days of ice is to be expected in the coastal waters, and in extremely cold winters as many as 175-215 days. 

In order to better understand the ice regime in the Baltic Sea and its changes in the past, present and future, it has been found practical not to analyze every single ice winter of the long-term series but to study classes of ice winters having similar characteristics. Some methods used to classify the ice winters in the different parts of the Baltic Sea are described below. 

1 Material Before the period of reconnaissance flights, which began in the 1920s, and the deployment of satellites in the 1960s, comprehensive observation data on ice 

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In 1989, the German Ice Seivice began using a new indicator in its classification of ice winters the accumulated areal ice volume (Koslowski, 1989). Several aspects render... 

This classification basically divides the ice winter into three different classes of ice severity type 1 (mild ice winters), type 2 (moderate winters) and type 3 (cold and severe ice winters). In the years 1956-2005, the values of the ice severity index 5 varied horn 0.1-0.72 for type 1 (10 winters), 0.92-3.24 for type 2 (28 winters), and 3.27-7.11 for type 3 (12 winters). 

Seina, A., Palosuo, E., 1996. The classification of the maximum annual extent of ice coverage in the Baltic Sea 1720-1995, based on the material collected by Risto Jurva (winters 1720-1940) and material of the Ice service of the Finnish Institute of Marine research (winters 1941-1995), Meri—Report Series of the Finnish Institute of Marine Research, No. 27, pp. 79-91. 

Table 4 presents the type of accidents occurred under ice conditions and their respective designated severity during the periods 2009-2013. Unfortunately, the data base of the winter 2002-2003 had not such classification. Thus, in winters 2009-2013, 3 accidents were designated as serious, and 16 cases were designated as less serious. There were not very serious accidents occurred under ice conditions during the analyzed time periods. 

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