Changes in frequency of Baltic Sea cyclones and their relationships with NAO and climate in Estonia

An increase in cyclone activity and the frequency of westerlies was observed over the Baltic Sea region during the 20th century.The Baltic Sea region itself is a relatively active area of cyclogenesis.Long-term changes in the frequency and mean sea-level pressure (SLP) of cyclones formed over the Baltic Sea region were analysed in the present study using the database of cyclones from literature.Relationships between the variables of the Baltic cyclones with the NAO index and some meteorological time series in Estonia were analysed.Results showed that the total number of cyclones did not change but the number and percentage of deep cyclones increased during 1948-2002.In general, the SLP of all cyclones and SLP in tracking points decreased.Correlation analysis showed that in case of the positive phase of the NAO, less but stronger cyclones form over the Baltic region.The Baltic Sea cyclones cause milder and moister weather conditions in Estonia in winter.