Seasonal fluctuations of the Baltic Sea level

Seasonal annual (Sa) and seasonal semiannual (Ssa) fluctuations are the dominant feature of long-period sea level variability in the Baltic Sea. Long-term series of observations (monthly mean sea level data) from the PSMSL database are used to estimate amplitudes and phases and to reveal spatial and temporal variations. It was found that the variations of seasonal amplitudes were quite significant from year to year and synchronous both within the Baltic Sea and in the Kattegat and Skagerrak straits. Climatologically averaged amplitudes and phases were calculated from 74 tide gauges, and the maps of spatial variability of seasonal constituents are plotted. The annual harmonic of the sea level gradually increases from the entrance (Danish Straits) to the heads of gulfs. The maximum amplitude of 12.7 cm is observed in the heads of the Gulf of Finland and Gulf of Bothnia. It is revealed that seasonal fluctuations in the Baltic Sea are caused by the zonal wind component.