Results of Observations
Although the new current sensing system measures lightning current derivatives with much better signal-to-noise-ratio than those measured by the old system, the number of current strokes measured by the new system in 1999 are too limited for proper statistical analysis. Therefore, only the statistical analysis of current waveforms captured by the old current sensing system are included in the paper.
Figure 2 shows the waveform of a lightning current derivative signal, captured by the old current sensing system at 17:49:36 on September 29, 1999 (the first of a three-stroke flash). The corresponding lightning current, obtained by numerical integration, is shown in Figure 3. Current reflections from the Tower’s structural discontinuities are clearly visible in both waveforms including the ground reflections arriving after about 3.2 us.