Extremes and decadal variations of the northern Baltic Sea wave conditions

Abstract

Average wave conditions, their seasonal cycle and decadal variations, and extreme wave storms in the northern Baltic Sea are studied on the basis of long-term time series from Almagrundet (1978-2003) and Vilsandi (1954-2005), and wave statistics from the middle of the northern Baltic Proper. The typical wave periods are 3-4 s in coastal areas and 4-6 s on the open sea. The monthly mean wave height varies from about 0.4 (0.5) m in April-July to 0.8 (1.3-1.4) m in January at Vilsandi (Almagrundet). The annual mean wave height varied insignificantly in the 1960s-1970s, considerably increased in the 1980s, was at highest in the mid-1990s, and rapidly decreases in 1998-2005. Significant wave heights H S ≥ 4m occur with a probability of about 1%. Extreme wave conditions with H S ≥ 7m have been registered five times since 1978. The records overlook 2-3 such cases. The overall recorded maximum H S is 7.8 m. The estimated maximum of H S was 9.5 m in cyclone Gudrun in January 2005. © 2008 Springer Netherlands.