A five-year analysis of ground truth data for positive flashes

Flashes with positive polarity, representing about 10 % of all cloud-to-ground flashes, were analyzed for this publication. Data from positive cloud-to-ground flashes recorded in the Austrian Alps over five years from 2015 to 2022 were used. The measurements were performed to record ground truth flash data at 23 selected locations and to compare their characteristics with values from the literature. The used measurement system consists of a high-speed Video camera and an electric Field Recording System (VFRS). Data of both systems are correlated with Lightning Location System (LLS) data by using a GPS time stamp. The overall dataset showed 107 positive flashes, comprising 121 strokes (11 multi-stroke flashes). The percentage of positive single-stroke flashes is 90 % for VFRS data and 84 % for LLS data. The mean multiplicity for VFRS data is 1.1. The LLS estimated median return stroke peak current of all analyzed positive strokes is 47.4 kA. The mean duration for 67 continuing currents of the 121 strokes is 126.1 ms. The detection efficiency of correctly detected positive flashes and strokes is 96.3 % and 89.3 %, respectively. A better understanding of positive flashes in general and in the Alpine region in particular shall be provided by the presented results.