A Cloud-to-Ground Lightning Climatology for Poland

Abstract

his research focuses on the climatology of cloud-to-ground (CG) lightning flashes based on PERUN lightning detection network data from 2002 to 2013. To present various CG lightning flash characteristics, 10 km ? 10 km grid cells are used, while for estimating thunderstorm days, circles with radii of 17.5 km in the 1 km ? 1 km grid cells are used. A total of 4 328 892 CG lightning flashes are used to analyze counts, density, polarity, peak current, and thunderstorm days. An average of 151 days with thunderstorm (appearing anywhere in Poland) occurs each year. The annual number of days with thunderstorms increases southeasterly from the coast of the Baltic Sea (15?20 days) to the Carpathian Mountains (30?35 days). The mean CG lightning flash density varies from 0.2 to 3.1 flashes km?2 yr?1 with the highest values in the southwest?northeast belt from Kraków-Cz?stochowa Upland to the Masurian Lake District. The maximum daily CG lightning flash density in this region amounted to 9.1 km?2 day?1 (3 July 2012). The monthly variation shows a well-defined thunderstorm season extending from May to August with July as the peak month. The vast majority of CG lightning flashes were detected during the daytime (85%) with a peak at 1400 UTC and a minimum at 0700 UTC. Almost 97% of all CG lightning flashes in the present study had a negative current, reaching the highest average monthly values in February (55 kA) and the lowest in July (24 kA). The percentage of positive CG lightning flashes was the lowest during the summer (2%?3%) and the highest during the winter (10%?20%).