Severity of winter seasons in the northern Baltic Sea between 1529 and 1990: reconstruction and analysis

This paper presents the reconstructed severity of winter seasons in the northern Baltic Sea on the basis of historical time series of ice break-up at the port of Riga (1529–1990). The winter seasons are classified as mild, average severe. Results of statistical analysis of time series of the date of ice break-up arranged according to the severity of winter seasons are given. A decreasing trend of about 2.0 d century–1 for the time series of ice break-up dates for severe winters is detected with statistical significance at the 99.9% level; for the mild and average winter seasons the trends are statistically insignificant.