Abstract

The work discusses the air temperature course of winter periods (December–March) in Poland in the years 1720–2015. The analysis is carried out for area mean values calculated from 5 stations: Szczecin, Wrocław, Warsaw, Wilno and Lwów. The time series of the mean area winter temperature (hereinafter PLZ) consists of combined observational (140 years) and reconstructed (156 years) data. PLZ reconstruction is based on independent variables, i.e. the values of the maximum area of the Baltic Sea covered with ice in the ice season and the monthly temperatures in January and March from the CET data set. The obtained correlations between independent variables and PLZ are strong, highly significant and stable. Statistical analysis shows that the course of PLZ is strongly correlated with a series of mean winter temperatures in Europe reconstructed by Luterbacher et al. (2006). In the analysed period of the years 1720–2015 the course of winter temperatures is non-stationary, there were periods of cooling and warming with different amplitude and duration. The variation range of PLZ falls within the limits from –6.24 (in 1929) to +3.35°C (in 1990). Winters with temperatures below 0°C account for 72% of winters in the examined period. Relatively mild winters dominated over Poland during the analysed period, with an average temperature ranging from –1 to 0°C and from 0 to 1°C, accounting for a total of 39.5% of all winters. The analyses show that the variability of PLZ in the entire examined period does not go beyond the limits of natural variability and the recent increase in PLZ is not unprecedented. Similarly strong temperature increases in winter temperatures were observed several times after the year 1720. The coldest winters occurred between the decades 1751–1760 and 1841–1850. The greatest variability of PLZ is observed in the twentieth century, when the coldest (1961–1970, decade mean PLZ –2.25°C) and the warmest decades (1991–2000, PLZ +0.02°C) occurred in the entire analysed period. The breakthrough in the course of PLZ, combined with the change in the thermal structure of winters, which can be identified with the end of the Little Ice Age, gradually occurred in the years 1858–1885 along with the increase in the intensity of the zone circulation. Changes in the solar constant and the frequency of volcanic eruptions did not affect the variability of winter temperatures.

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