The mathematical expression of such factors has to be yet developed for storm situations. The world literature contains shallow-water factors for tides, i.e. regular, periodic sea level changes. A very active low pressure system which advected over

the southern Baltic produced a rapid sea level rise. This system passed from the south of England via the North Sea coast to the southern Baltic coast, from where it moved on to the Gulf of Finland (Figure 1a). The high horizontal pressure gradient component in the western part of the system was accompanied by a strong, gusty, north-westerly wind. The entire Polish coast experienced a rapid sea level rise (maximum of 617 cm, i.e. 117 above zero N.N., at Świnoujście

on the western FAK inhibitor part of the coast, 635 cm at Kołobrzeg, and 615 cm at Gdańsk on the eastern part of the coast) (Figures 1b, c). The low was moving from over the Pomeranian Bay towards the eastern part of the coast with a mean velocity of 50 km h−1 and passed over the Polish coast in the space of 6 hours. The low pressure system’s velocity affected not only the magnitude of the sea level rise, but also its intensity. All the gauges showed only the positive phase of the sea surface deformation. On 17 January 1955, the wind at Świnoujście changed direction from S to SW and NW, and could not, by itself, have generated the surge. The contribution of the baric wave to the surge is obvious and visible in Figures 1a–1c and in Figure 2, which shows a rise in sea level Tacrolimus mw of 90 cm during 2 hours and a fall of 90 cm during 4 hours. A deep and active low pressure

system from over the British Isles was moving at a velocity of 70 km h−1 over Denmark and southern Sweden, the Baltic Sea and on towards the north-east into the White Sea (Figure 3). The storm wind and baric wave generated by the system induced extremely large variations in the Baltic sea level. The rapid passage of the low over the Baltic resulted in a characteristic Regorafenib molecular weight sea level fall on the Polish coast on the morning of 18 October. At Świnoujście, the absolute 1946–2006 minimum of 366 cm was recorded. The low’s centre moved that day over the Åland Archipelago. For some hours the southern Baltic, left in the rear of the baric system, experienced severe north-westerly and northerly winds. The return to equilibrium proceeded through wind-induced seiche-like changes in the sea level. At Świnoujście and Kołobrzeg, the sea level changes during 8 h had an amplitude of about 2 m (Figure 4). It should be pointed out that, when the baric low movement is close to the value of gH, as was the case in the event of 17–19 October 1967, the denominator of formula (2) tends to 0. In this case, formula (2) suggests that the storm situation should be covered by the resonance zone, and the result of the calculations is not reliable.