High‐Energy Radiation From Natural Lightning Observed in Coincidence With a VHF Broadband Interferometer

Abstract

This work presents the first simultaneous X‐ray measurements from natural lightning in coincidence with a very high frequency (VHF) broadband interferometer. During an observational campaign in north‐central Colombia, five intense X‐ray bursts were detected from negative stepped leaders and two X‐ray emissions from a dart leader. Thanks to the high angular and time resolution of the interferometer, it was possible to locate the origin of high‐energy radiation during the lightning leader propagation. We study the correlation with VHF pulses and the two‐dimensional speed of the leader channels. A strong temporal correspondence has been observed between the high‐energy emissions and the most intense VHF pulses, which suggests the runaway electrons as a shared mechanism. The observations show that an X‐ray burst can have multiple high‐energy sources belonging to different leader branches, that can be several hundreds of meters apart. Therefore, from a spatial point of view, not a unique origin has to be searched, but an extensive origin of the X‐ray burst should be considered. We hypothesize similar conclusions in particular for downward TGFs and maybe for TGFs in general.

Multi‐Stroke Positive Cloud‐To‐Ground Lightning Sharing the Same Channel Observed With a VHF Broadband Interferometer

“…The subsequent DPL is faster, following a pre‐ionized channel, its average 2D speed is quite constant at 1.3 × 10 7 m/s and slightly accelerating in the last 20 μs to 2.0 × 10 7 m/s. This speed range is very similar to the speed of dart leaders following negative CG strokes (e.g., Urbani et al., 2021) and the recent measurements of Zhu et al. (2021).…”

“…The data presented in this work were recorded during an observational campaign at the Universidad Industrial de Santander campus of Barrancabermeja (Colombia) in autumn 2019. Instruments, processing techniques, and the deployment of the instrumentation are further described in Urbani et al (2021) and in the Supporting Information S1.…”

“…Instruments, processing techniques, and the deployment of the instrumentation are further described in Urbani et al. (2021) and in the Supporting Information .…”

“…We designed and built our version, which consists of three VHF antennas (20-80 MHz bandwidth) deployed along two orthogonal baselines of 22 m. The digitizer used for the acquisition system is a GaGe Razor Express 1,604 with four channels, 16-bit resolution, and 200 MS per second sampling rate. The interferometric processing technique is a window-based cross-correlation method (Stock et al, 2014) improved by a clustering algorithm to average overlapping solutions and perform noise reduction (Urbani et al, 2021). The time window length used is 512 samples (2.56 ns), timing uncertainty, and angular resolution are reported in the Supporting Information S1.…”

A New Hybrid Algorithm to Image Lightning Channels Combining the Time Difference of Arrival Technique and Electromagnetic Time Reversal Technique

“…For example, for very-low-frequency (VLF) or low-frequency (LF) band signals, time of arrival (TOA) or time difference of arrival (TDOA) method (e.g., [2][3][4][5][6][7][8][9]) or artificial intelligence technology [10] have been applied. For electromagnetic signals in a very-high-frequency (VHF) band, lightning location methods are commonly carried out using the interferometry (INTF) or TDOA technique (e.g., [11][12][13][14][15]). Recently, Mora et al [16] and Lugrin et al [17] introduced the electromagnetic time reversal (EMTR) method to locate lightning strikes.…”