Characterization of the initial stage in upward lightning at the Gaisberg Tower: 1. Current pulses

We examined current waveforms for 58 upward flashes occurring in 2006–2014 initiated from the Gaisberg Tower located near Salzburg, Austria. The initial stage (IS) of these comprised relatively slowly varying “background” current, with faster, more impulsive variations overlaid on this background current. In 46 (79%) continuing was negative, and other 12 (21%) it bipolar. 1180 pulses occurred during IS flashes, which 708 (60%) were positive bipolar (positive polarity a negative opposite overshoot), 28 (2.4%) unipolar no 440 (37%) unipolar, four (0.3%) pulses. found that only at early times. divided into two phases: (1) leader initiation propagation phase (IPP) (2) mature (MP). 901 or 76% (712 189 unipolar) IPP, 279 21% (unipolar) MP. median background-to-peak 134 A IPP 687 MP