Properties of Three Types of M-Components and ICC-Pulses From Currents of Negative Upward Lightning Measured at the Peissenberg Tower

Channel base currents from natural lightning have been measured on the new top structure of the Peissenberg Tower, Germany, since 2008. Here, an analysis is given of the impulsive currents, called initial continuous current (ICC)-pulses, that occurred during the ICC, and of the impulsive currents, called M-component currents, that occurred during the continuing current following return strokes. It was found that the M-component currents and the ICC-pulses closely resemble each other. The 45 flashes analyzed were exclusively negative upward lightning containing 60 return strokes and 264 impulsive currents (79 M-components and 185 ICC-pulses). A total of 246 (93.2%) impulsive currents were negative ones, and 18 (6.8%) impulsive currents were positive ones. The majority of 83.7% were pure impulsive currents and the minority of 16.3% were combined impulsive currents composed by two or more pure impulsive currents. For the pure impulsive currents, the analysis revealed three different types of waveforms for both the M-component currents and the ICC-pulses. The currents of the first type have a more or less symmetrical wave shape. For the 27 M-component currents and the 103 ICC-pulses (values in parentheses) of the first type, the geometric mean values are 0.7 (0.5) kA for the peak value, 23.9 (24.7) μs for the 10%-to-90% risetime, 101.0 (96.5) μs for the full width at half-maximum (FWHM), and 94.3 (57.1) mC for the transferred charge. The impulsive currents of the second type have a bipolar wave shape with current reversal. For the 31 M-component currents and the 37 ICC-pulses of the second type, the geometric mean values are 0.9 (0.6) kA for the peak value, 11.8 (16.9) μs for the 10%-to-90% risetime, 60.6 (74.7) μs for the FWHM, and -42.4/58.5 (-34.1/26.5) mC for the negative/positive charge of the bipolar pulses. The impulsive currents of the third type have a wave shape, which exhibits a fast rise to peak and a much longer decay to low current values. For the 5 M-component currents and the 18 ICC-pulses of the third type, the geometric mean values are 1.0 (1.2) kA for the current peak, 1.2 (2.9) μs for the 10%-to-90% risetime, 56.8 (29.0) μs for the FWHM, and 44.8 (24.03) mC for the transferred charge.