Abstract
Keywords Lightning; Upward lightning; Initial stage; Electric field measurements; Electric field signatures; Gaisberg Tower Highlights * Near and far electric field signatures of IS current pulses were analyzed. * Electric field signatures of early-stage-IS bipolar current pulses were characterized. * Such bipolar pulses could be associated with upward leader inception. We examined the characteristics of electric field signatures occurring during the initial stage of 58 flashes measured simultaneously at near (170 m) and far (79 or 109 km) distances from the Gaisberg Tower located near Salzburg, Austria. Of the 340 field signatures measured at the near station, 68 (20%) were associated with current pulses occurring during the initiation and propagation phase (IPP) of the upward leader, and 272 (80%) were associated with pulses that occurred during the mature phase (MP) of the upward leader. Of the 68 field signatures of IPP pulses, 40 were associated with bipolar (IPP-B type) current pulses and 28 were associated with unipolar (IPP-U type) current pulses. Field signatures of IPP-B pulses were only detected at the near measurement station and appear to be associated with currents in relatively short (meter-scale) channel segments formed during the upward leader inception. At the far stations, field signatures of 84 IS pulses were recorded and analyzed. There was modest correlation between the background-to-peak current of IS pulses and near and far electric radiation field changes as well as between radiation field changes recorded at near and far distances. Author Affiliation: (a) Department of Aerospace, Physics and Space Sciences, Florida Institute of Technology, Melbourne, Florida, United States of America (b) Austrian Lightning Detection and Information System, OVE Service GmbH, Vienna, Austria (c) Now at the Department of Chemistry and Physics, Gulf Coast University, Fort Myers, Florida, United States of America (d) Los Alamos National Laboratory, Los Alamos, New Mexico, United States of America * Corresponding authors. Article History: Received 2 February 2022; Revised 20 June 2022; Accepted 11 July 2022 Byline: Naomi Watanabe [nwatanabe@fgcu.edu] (a,c,*), Amitabh Nag [anag@fit.edu] (a,d,*), Gerhard Diendorfer (b), Hannes Pichler (b), Wolfgang Schulz (b), Hamid K. Rassoul (a)