Initial Current Variation of the ICC Considering the Negative Upward Lightning Measured at the Peissenberg Tower, Germany

The objective of this study is the analysis of the initial current variation of the initial continuous current (ICC) of the negative upward lightning measured at the Peissenberg Tower, Germany. Out of the total of 152 upward lightning, 100 (65.8%) contained an ICC, which increased smoothly after the onset of the current. In contrast, in 52 (34.2%) cases, the initial stage of the ICC was characterized by an initial current variation forming a significant initial peak. On average, the peak exceeded the pure ICC by a factor of 4, the maximum of the peak was 737 A, the peak duration was 33 ms, and the charge stored in the peak was 6.79 C. This relatively high amount of charge is comparable with the charge of the first negative return stroke of downward flashes. Nearly, half (47.7%) of the ICC
_P
flashes (with ICC pulses > 2 kA), 33.3% of the ICC
_RS
flashes (with at least one succeeding return stroke), 28.9% of the ICC
_Only
flashes (without significant ICC pulse), 30% of the self-initiated ones, and 42.3% of the other- triggered ones had such a pronounced initial current peak. In 93.1% of the cases, the initial current peak was superimposed by a pulse train, which contained high-frequency current pulses with amplitudes up to 4.5 kA and which lasted up to 40.8 ms.