This resulted in a small decrease in the water level in the western Baltic (Gedser − 36 cm, Kiel − 56 cm) and the filling up of the Baltic Sea in the eastern and northern part (Klaipeda + 84 cm, Ristna + 113 cm, Hamina + 121 cm) (Figure 11). The next day,

8 January, the mid-latitude depression Gudrun left Scotland and moved at a speed of 60 km h− 1 across the North Sea into the southern part of the Gulf of Bothnia, where the pressure fell to 961 hPa (9 January, 00 UTC) (Figures 10a,b). On 8 January 2005, the wind speed increased to 20 m s− 1 throughout the Baltic Sea region. Such a quick passage of the depression caused deformations of the this website Baltic Sea surface. A slight rise in sea level and a subsequent rapid decrease CDK activity were observed in the western part of the Baltic towards the end of 8 January (Frederikshavn, from + 99 to − 40 m, Gedser, from + 26 m to − 136 m, Kiel, from 0 to − 153 cm) (Figures 11, 12a). At the same time, in the north-eastern Baltic, sea levels rose sharply to extreme values (Klaipeda + 146 m, Ristna + 222 m, Hamina + 194 m) (Figures 11, 12b,c). On 9 and 10 January 2005, depression Gudrun moved north-eastwards through southern Finland to western Russia (Figures 10b, c). A change in the deformation phase of the

Baltic Sea surface occurred. Sea levels rose sharply in the western Baltic (Gedser + 68, Kiel + 58 m) but dropped in the eastern part of the sea (Figures 11, 12d). The occurrence of extreme sea levels, which are the result of storm surges on the Baltic coasts, depends on three components: – the volume of water in the respective basins of the Baltic Sea (the initial sea level prior to the occurrence of an extreme event), The volume of water filling a water basin Protein Tyrosine Kinase inhibitor prior to an extreme sea level has been stated in a few publications in the context of the Polish coast (storms in the southern Baltic) (Wiśniewski, 1996, Stanisławczyk and Sztobryn, 2000, Sztobryn et al., 2005 and Wiśniewski

and Wolski, 2009a). For example, the volume of water filling a basin was determined by calculating, on the basis of observations, the mean sea level along the Kołobrzeg-Kungsholmsfort transect or by reference to records from other ports like Degerby, or other transects in the Baltic (Stanisławczyk & Sztobryn 2000). In general, the water exchange between the North Sea and the Baltic and changes in the Baltic water volume produced by long-lasting stationary pressure systems were described by Wielbińska (1964). In the context of the two storm situations analysed in this work, basin filling is represented by the starting (reference) sea level prior to the changes caused by the storm (Table 5).