LiOn return stroke peak current analysis for ground strike points in the Austrian alps

This paper presents an analysis related to the research project 'Lightning Observation in the Alps' (LiOn) carried out by Graz University of Technology in cooperation with the Austrian Lightning Detection and Information System (ALDIS). Atmospheric discharges were observed at 21 different measurement locations in Austria by using a video and field recording system. The system consists of two main components, a high speed video camera and a flat plate antenna. The recorded ground truth data should help to get additional information about atmospheric discharge processes, especially in the alpine area. For this analysis, a dataset of negative cloud-to-ground strokes of the measurement periods 2015, 2017 and 2018 was used. In this analysis, we compare peak currents of first return strokes (LLS flash data) with peak currents of first strokes in a GSP. The GSPs are determined manually by using the video data. We especially considered the relation of first initial (FI) peak currents versus subsequent (SU) peak currents. The stroke peak current versus the multiplicity for flashes and strokes per GSP was investigated too. For all the analyses in this paper, the Austrian Lightnig Location System (ALDIS) provided the data for the stroke peak currents. In 42 % of the flashes, at least one SU peak current in a flash shows a greater value compared to the FI stroke in this flash. Checking the peak currents within GSPs reveals 37 % with at least one SU stroke with a larger peak current than the FI stroke in the same GSP. The analysis of the percentage of SU strokes with peak currents greater than the FI stroke reveals the same value of 14 % for flashes and per GSPs. Regarding the analysis of FI peak currents versus the multiplicity, the results show an increase for both analyses leading to higher peak currents for the FI strokes exhibiting a larger multiplicity.