Change of Atmospheric Circulation

The changes and variability of atmospheric circulation over Poland were analysed using several methodological approaches containing different spatial scales. The traditional manual classifications by Niedźwiedź and the well-known Grosswetterlagen were used. Simultaneously, an automatic classification was made by Ustrnul and Litynski and the NAO index was also measured for mutual comparison. All of the analyses concerned basically the main period of 1951–2018. However, thanks to the availability of the data from Niedźwiedź calendar of circulation, it was possible to extend the time series back to 1873. All of the analyses confirmed that Poland is significantly affected by the westerly circulation, which has a major influence on the formation of the climate. Throughout the entire long period from the end of the nineteenth century to the present day, its large fluctuations and a generally weak increasing trend were found. A similar situation can be also seen for the period 1951–2018, however, an increased westerly circulation was detected in the 1980s and 1990s. The turn of the 1960s and 1970s marked the weakening of this circulation pattern, as did the last 10 years. Generally, a high level of comparability in the course of circulation indices according to the classifications of Niedźwiedź, Ustrnul, Litynski and the Grosswetterlagen was found.