Wavelet analysis of chaotic pulse trains prior to subsequent return strokes in Malaysia

Abstract

This paper presents a wavelet transformation of chaotic pulse trains (CPTs) prior to negative subsequent return strokes in Malaysia. A total of 593 recorded waveforms were examined. Even though several hundred waveforms were identified as containing CPTs, only 47 waveforms with CPTs preceding subsequent return stroke were selected for analysis. 19 samples are classified as CPTs associated with dart or dart-stepped leader (Type 1 CPTs) with spectral and spread regions average frequency range of 34.8–154.3 kHz and 56.2–81.4 kHz respectively. 28 samples are classified as chaotic pulse trains alone (Type 2 CPTs) with spectral and spread regions average frequency range of 24.6–121 kHz and 40.3–62 kHz, respectively. The Type 1 CPTs tends to radiate at a higher frequency range compared to Type 2 CPTs. The maximum power radiated by the largest pulse in Type 1 CPTs is more than six times larger than that for the Type 2 CPTs. In addition, the Type 1 CPTs have larger electric field variations, higher frequency, and higher power radiated spectrum compared to Type 2 CPTs. The reported radiated energy can be further compared with other lightning activities to give a better insight on the in-cloud breakdown processes prior to subsequent return strokes.