Long-term variability of thunderstorm occurrence in Poland in the 20th century

Abstract

The main aim of this study was to present thunderstorms' occurrence in Poland in the 20th century. The paper also attempts to assess the impact of atmospheric circulation on the variability of number of days with thunderstorms and estimate synoptic conditions conducive to the formation of thunderstorms. The analysis was based on thunderstorm observations from 56 synoptic stations in Poland in the period 1951–2000 and 7 stations for the years 1885–2000. In the second part of the study, the types of synoptic situations elaborated by Osuchowska-Klein, the types of synoptic situations by T. Niedźwiedź, indices of atmospheric circulation by Z. Ustrnul and index of North-Atlantic Oscillation (NAO). As a result, it was determined that during the analysed period, no tendency was found in the multi-annual course of mean yearly number of days with thunderstorms in Poland, and the values usually do not differ much from the value typical for the climatic–geographical region in which Poland is situated. Synoptic situations have less influence on thunderstorm occurrence than that usually suspected. The eastern advection has the largest influence on the occurrence of the days with thunderstorms, especially in southern Poland. The analysis of relations between the variability of number of days with thunderstorms and the changes of the circulation indices proved these regularities.