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EN
In the paper the influence of atmospheric circulation on selected dangerous weather phenomena in Europę in the year 2000 has been presented. Dangerous weather phenomena include: 30 days with thunderstorms in Poland and 26 examples of such phenomena in Europę (tornados, strong winds, thunderstorms, torrential rains, floods, etc.). The NAO index (North Atlantic Oscillation) served to determine the character of the circulation that influenced the occurrence of catastrophic phenomena in Western, Central and Southern Europę. The J. Lityński classification of circulation types was used to thunderstorms occurring in Poland only. Most catastrophic phenomena during the positive NAO phase (predominance of zonal circulation) happened in Western and Central Europę. During the negative NAO phase (predominance of meridional circulation) the regions of the Mediterranean Basin were more freąuently affected. In the case of thunderstorms in Poland in the year under investigation (2000) their occurrence was related to the inflow of air masses from the northern sector.
EN
The aim of the study is to show and compare variation of the annual and daily course of thunderstorms in selected European cities in 2005-2009. Data on thunderstorms originate from dispatches METAR for three airport stations: London Gatwick, Warsaw Okęcie and Moscow Sheremetyevo. These cities represent the various types of climate: warm temperate marine, transitional and continental. Thunderstorms mostly occurred in Warsaw - 207 (Moscow - 174, London - 71). The maximum of thunderstorms frequency, in the yearly course, in all towns occurred in July (Warsaw - 11,8; Moscow - 13,4; London - 5,0). Thunderstorms predominantly started at 13:30 in London, 17:00 in Warsaw, 18:00 in Moscow (13:30 means period 13:01-13:30, 17:00 means period 16:31-17:00 etc.). Thunderstorms most often ended at 13:30 in London, 17:00 in Warsaw, 20:30 in Moscow. There were dominated, at all stations, brief thunderstorms, which lasted for 30 minutes. The longest thunderstorm remained 9 hours (Warsaw), 5,5 (Moscow), 4,5 (London).
PL
W pracy przedstawiono zróżnicowanie przestrzenne i zmienność czasową pojawiania się burz i opadów gradu w Polsce. W badaniach wykorzystano serie obserwacyjne z 24 stacji meteorologicznych z lat 1949 – 2006 oraz, w przypadku informacji o burzach, z 8 stacji z okresu 1885 – 2008. Stwierdzono, że nie można jednoznacznie potwierdzić ani wzrostu, ani liczby dni burzowych, ani liczby dni z opadem gradu w ostatnich dziesięcioleciach. Na większości stacji położonych na północny zachód od linii łączącej Śnieżkę i Suwałki liczba dni burzowych zmniejszała się, natomiast na stacjach leżących na południowy wschód od tej linii przeważały tendencje dodatnie. Ważną cechą przedstawianych zmian jest ich regionalne zróżnicowanie związane z dominującymi w danym obszarze sytuacjami synoptycznymi oraz wpływem lokalnych warunków przyrodniczych. Jest ono szczególnie silnie widoczne w rocznym przebiegu częstości badanych zjawisk. Na północy kraju okres ich największej częstości jest znacznie dłuższy, a liczba dni z burzą wyraźnie mniejsza i bardziej równomiernie rozłożona w czasie niż na południu Polski. R oczne maksimum występowania burz przypada na lato, ale występowały także ciągi lat, w których przypadało ono na wiosnę lub wczesną jesień. Dni z gradem występują natomiast głównie w miesiącach wiosennych (kwiecień–czerwiec), stanowiąc wtedy od 25 do 60 % ich częstości. Na stacjach położonych na północy i w zachodniej połowie kraju zaznacza się dominacja gradu występującego wiosną, na południu Polski natomiast jego przebieg jest bardziej wyrównany, a maksimum występowania częściej jest przesunięte w kierunku miesięcy letnich.
EN
This paper is focuses on thunderstorms and hails in an attempt to address one of the most pressing issues in the debate on climate change, which is to understand sources of extreme meteorological and climatological phenomena. The study used records of observations at 24 weather stations covering the period 1949 – 2006 and thunderstorm details from eight stations in the period 1885 – 2008. The study identified no clear trend in the number of days with thunderstorms or with hails during the study period. For both phenomena there is a strong regional variation, both annually and in the long-term. This kind of spatial variation in the occurrence of thunderstorms and hails is characteristic of these phenomena in many areas of the world (Changnon 1988; Brázdil et al. 1998; Kuleshov et al. 2002). In Poland most of the stations that recorded a decrease in the number of days with thunderstorms after 1949 were found north of the line connecting Mt. Śnieżka in the southwest and the town of Suwałki in the northeast and the greatest decrease in this number was recorded in Słubice at 1.3 days per 10 years. A trend to an increase in the number of days with thunderstorms was observed south of the line. The greatest increase in the number of days with thunderstorms was recorded in Włodawa (1.7 days per 10 years), Lesko (1.6 days) and Katowice (1.1 days). Additionally, the study revealed that during the second part of XX century there was an increase in the number of days with thunderstorms in the cool half of the year at most of the stations involved. The pattern was particularly strong to the south of the Śnieżka-Suwałki line and in Szczecin. With the time scale expanded to the period 1885 – 2008, the changes are weaker, which clearly suggests that any patterns that emerge depend on the study period chosen. The spatial and temporal variabilities in the two phenomena are caused by the dominant types of atmospheric circulation and by regional differences in environmental conditions. Numerous authors have also suggested a link between changes in the occurrence of thunderstorms and hails and macroscale changes in the atmospheric circulation (Kamyshanova 1974; Changnon 1985). On the one hand, in some regions the influence of characteristic synoptic situations may be stronger than the dominant large-scale atmospheric circulation (Bielec-Bąkowska 2002, 2003), while on the other, local conditions are potentially an important factor leading to the free convection conducive to thunderstorms and hails. This seems to be a very important consideration in analysing hails, especially when they accompany thermal thunderstorms. An example is provided by an increased occurrence of these phenomena in an area of Poland that was up to 80 metres higher in altitude than an area, from which the air arrived (Zinkiewicz, Michna 1955; Koźmiński 1965). The annual pattern of hails occurrence seems to be its most significant characteristic. A springtime maximum dominates at stations in the north and in the western half of the country, while a far more even distribution with a maximum shifted towards the summer season is found in the south of Poland. The long-term record of days with hails was very even at most of the stations and periods with significantly higher or lower number of days with hail occurred at most of the stations simultaneously are also difficult to find.
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