Sea level oscillations

Strong winds can cause a set-up in the Baltic Sea level, pushing the water up against the coast, so that there is a (gentle) slope in sea level from one side of the sea to the other. As the wind changes, it can no longer maintain this sea level slope, and the water is released starting an oscillation – a seiche - like water in a bath tub.

The oscillations continue back and forth many times, being slowly dissipated by friction. The resulting effect is a standing wave. The period between two high water incidents is governed by the depth of water and the breadth of the sea area. Oscillations in the Baltic from north to south have a period of 4 days and may continue for several weeks. The amplitude in northern Sweden can reach 50 cm.

Another oscillation can form between the Gulf of Finland and the south western Baltic. This seiche has a period of 27 hours. These oscillations have least effect in the middle of the sea. The sea level station at Landsort is relatively central to the Baltic and so is not much affected by these oscillations. As a result, sea level measurements from Landsort are a good guide to the water level in the Baltic over longer time periods.