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Atmospheric circulation and sounding-derived parameters associated with thunderstorm occurrence in Central Europe

Kolendowicz, Leszek, Taszarek, Mateusz, Czernecki, Bartosz
Atmospheric research 2017 v.191 pp. 101-114
atmospheric circulation, autumn, cold season, convection, convective available potential energy, mixing, spring, storms, summer, temperature, warm season, wind, winter, Central European region, North Sea, Scandinavia
The main objective of this study is to examine the influence of atmospheric circulation patterns and sounding-derived parameters on thunderstorm occurrence in Central Europe. Thunderstorm activity tends to increase as one moves from the north to the south of the research area. Maximal thunderstorm occurrence is observed in the summer months, while between October and March such activity is much lower. Thunderstorms are also more frequent in spring than in autumn. In the warm season, the occurrence of thunderstorm is associated with the presence of a trough associated with a low located over the North Sea and Scandinavia. In the cold season, the synoptic pattern indicates a strong zonal flow from the west with significantly higher horizontal pressure gradient compared to the warm season. Thunderstorms are more likely to form when the boundary layer's mixing ratios are higher than 8gkg⁻¹. Deep convection is also more likely to occur when the vertical temperature lapse rates (between 800 and 500hPa pressure layers) exceed 6°Ckm⁻¹. During the cold season, considerably higher lapse rates are needed to produce thunderstorms. The values obtained for the convective available potential energy indicate that at least 50Jkg⁻¹ is needed to produce a thunderstorm during wintertime and 125Jkg⁻¹ during summertime. Cold season thunderstorms are formed with a lower instability but with a more dynamic wind field having an average value of deep layer shear that exceeds 20ms⁻¹. The best parameter to distinguish thunderstorm from non-thunderstorm days for both winter and summer months is a combination of the square root of the convective available potential energy multiplied by the deep layer shear.