Study on frequency spectra and image of negative cloud to ground lightning flashes with a very high frequency detecting system

The spectral analysis of lightning radiation plays a vital role in understanding lightning discharge physics and improving the design of protection systems against lightning-induced electromagnetic disturbances. This study analyzes the spectral characteristics of very high frequency (VHF) electric field emissions in relation to low-frequency (LF) field variations during different physical phases of thirteen negative cloud-to-ground (CG) lightning discharges. Instantaneous frequency analysis revealed that the frequency components associated with the initial breakdown (IB), stepped leader (L), return stroke (RS), and continuing current (CC) phases ranged from 20–48 MHz, 25–65 MHz, and 29–68 MHz, respectively. The mean frequencies were 38 MHz for IB, 43 MHz for L, and 39 MHz for CC. These findings provide insights into the spectral behavior of VHF radiation during distinct lightning processes, enhancing understanding of lightning electromagnetic emissions and their implications for atmospheric electricity and protection research. Variations within the 20–68 MHz range among lightning events indicate that each discharge may involve unique underlying mechanisms. The results emphasize the significance of frequency-domain characteristics for distinguishing between lightning phases. Additionally, recorded electric field signals were processed using a time-reversal technique to reconstruct a spatial image of the negative CG lightning channel.