Close and Distant Electric Fields due to Lightning Attaching to the Gaisberg Tower

We examine current and electric field waveforms produced by lightning strikes initiated from the Gaisberg Tower located in Salzburg, Austria. Current was measured at the top of the tower and electric field measured simultaneously at close (170 m from the tower), and far (79 or 109 km from the tower) distances. In this preliminary study, we establish the criteria for characterizing current and electric field pulses that occur during the initial stage of upward lightning flashes (including those at the initiation of the initial stage) based on the characteristics of the measurement system used to record the current and electric field waveforms and the occurrence context of the pulses in the flash. Of the seven negative upward flashes analyzed in this study, two flashes had bipolar IS background current, which were first negative, followed by brief (duration < 2 ms) positive current, and then negative again. The initial stage background current was negative in the other five flashes. Overall, 70% of the pulses occurring during the initial stage were positive bipolar, 2.1% were positive unipolar, and 28% were negative unipolar. No negative bipolar pulses were found. The total duration of unipolar pulses ranged from 4.9 to 702 mu s and that of bipolar pulses ranged from 4.5 to 197 mu s.