Long-term changes in the frequency of cyclones and their trajectories in Central and Northern Europe

Changes in the number of cyclones and cyclone trajectories in Central and Northern Europe during 1948-2000 are analysed using a database of cyclones. Two hypotheses are advanced. Firstly, the number of cyclones reaching Northern Europe has increased, causing a transition to a more maritime climate. Secondly, the trajectories of cyclones have moved northward, causing the advection of warm and moist air to Northern Europe and decreasing precipitation in Central Europe. These advances were confirmed by data analysis. A linear trend and its statistical significance (P < 0.05) for the frequency of cyclones in the Atlantic-European sector (30 degrees W-45 degrees E, 35-75 degrees N) were calculated. Circles with radii of 500, 1000, 1500 and 2000 km with centre coordinates 60 degrees N and 22.5 degrees E were generated. All the cyclones whose centres were located within these circles were counted. Also two meridians -5 degrees E and 20 degrees E - were selected and all the cyclones were counted whose centres crossed the meridians from west to east in the interval of 45 - 75 degrees N. Changes in the frequency of long-term cyclones were analysed. The number of cyclones reaching Northern Europe has increased in the period 1948 - 2000. The number of cyclones over the Baltic Sea has increased, especially in the winter. In Central Europe, the number of cyclones has decreased, especially in the warm half-year. The number of long cyclones has increased over the Baltic Sea, especially in the cold half-year.