Formation factors of the most electrically active thunderstorm days over Poland (2002-2020)

This research documents atmospheric conditions and development of high electrically active thunderstorm days that occurred over Poland in period 2002-2020. The 8 days with the highest number of detected cloud-to-ground flashes during one storm cell life cycle were analyzed. The study used data from the PERUN lightning detection and location system, ERA5-reanalysis, vertical atmospheric soundings, and synoptic maps as well. As a result of the analysis, it can be concluded that the development of thunderstorms is positively influenced by the lowpressure area above the North Sea and the atmospheric fronts with zone of wind convergence in the lower troposphere. The analyzed storm systems on the analyzed days were created in the atmosphere of a high vertical wind shear (from 10 to 18 m s(-1)), lifted index (from +0.04 to -8.22), thermodynamic instability (CAPE 1000-3700 J kg(-1)), rich boundary layer moisture (mixing ratio: 12-14 g kg(-1)), and high tropospheric moisture (total column water vapour >50 kg m(-2)). Very moist air masses ahead of the storm systems provided consistent access to large amounts of latent heat released into the clouds and intensified upward mass fluxes and development of intense lightning activity from Cumulonimbus cloud.