Spatial Diversity of Cloud-to-Ground Lightning Flashes in the Kujawsko-Pomorskie Voivodeship (Poland), 2002-2019

Abstract

This research focuses on the spatial diversity of cloud-to-ground (CG) flashes in the Kujawsko-Pomorskie voivodeship (Poland) based on data from the PERUN lightning detection system, 2002-2019. The storm season usually lasts from May to September, with July having the highest number of thunderstorms days and flashes. Thunderstorms most often occur in the afternoon. A generated grid of 5×5-km cells was used to characterise the variables related to CG flashes. In the analysed period 432,925 CG flashes were detected in the voivodeship (24,051 flashes year-1). The highest electrical activity was found in the south-eastern part of the province. In grids with a large water surface, the number of CG flashes was small and increased with distance from the Vistula River. The distribution of atmospheric discharges in major cities of the region (Bydgoszcz, Toruń, Włocławek and Grudziądz) was random. Years with greater electrical storm activity (27,614 discharges in 2017) are interspersed with calmer years (5000-7000 discharges). There were found an upward trend in lightning discharges (of 1681 discharges year-1) during period 2002-2019. To develop maps specifying the number of thunderstorm days, a 1×1-km grid cell was used with a 15-km radius buffer from the bin centre. The annual number of thunderstorm days in the voivodeship fluctuates from 27 to 41 days and increases from north-west to south-east. Consecutive days with a thunderstorm, the most common runs are of three days in a row with a storm. The number of thunderstorm days shows an increasing trend (0.82 days year-1). This trend is related to the increase in air temperature in the storm season (Apr-Sept) reaching (0.04°C/year).