Baltic Sea extreme sea levels 1948-2011: Contributions from atmospheric forcing

Extreme sea levels in the Baltic Sea are usually analyzed from tide-gauge data covering more or less extended periods. More comprehensive spatial or systematic analyses are less frequently available. Data from a high-resolution tide-surge model driven by high-resolution reanalyzed atmospheric fields reconstructing Baltic Sea sea levels from 1948 to 2011 on an hourly basis are analyzed. Meteorologically induced sea levels are characterized by pronounced annual to decadal fluctuations and a typical seasonal distribution comparable to the variability in regional wind climate. No substantial long-term trends over the considered period could be detected. Wind set-up represents the most dominant factor, however, short term variations in the filling levels of the basin and seiches contributed substantially to some of the observed peak water levels in the past. For the tide-gauge Wismar at the German Baltic Sea coast, it is exemplarily demonstrated that storm surges during periods with and without high filling levels occurred at about equal shares. When high filling levels were present, lower wind speeds were generally needed to sustain comparable peak water levels. Seiches also contributed to some of the observed extremes usually with a preferred phase shift. For Wismar, in about one third of the cases contribution from seiches at peak water level was found to exceed 10 cm.