Lightning initiation: Strong pulses of VHF radiation accompany preliminary breakdown

Abstract

We analyze lightning initiation process using magnetic field waveforms of preliminary breakdown (PB) pulses observed at time scales of a few tens of microseconds by a broad-band receiver. We compare these pulses with sources of narrow-band very high frequency (VHF) radiation at 60–66 MHz recorded by two separate Lightning Mapping Arrays (LMAs). We find that almost none of the observed PB pulses correspond to geo-located VHF radiation sources, in agreement with previous results and with the hypothesis that processes generating VHF radiation and PB pulses are only weakly related. However, our detailed analysis discovers that individual peaks of strong VHF radiation seen by separate LMA stations correspond surprisingly well to the PB pulses. This result shows that electromagnetic radiation generated during fast stepwise extension of developing lightning channels is spread over a large interval of frequencies. We also show that intense VHF radiation abruptly starts with the first PB pulse and that it is then continuously present during the entire PB phase of developing discharges.

Initial Breakdown Pulses Accompanied by VHF Pulses During Negative Cloud‐to‐Ground Lightning Flashes

“…In conclusion, using simultaneously sampled broadband FA and narrowband LogRF waveforms we have verified the hypothesis of Kolmašová et al () that classical IB pulses are systematically accompanied by VHF radiation and that most larger‐amplitude IB pulses are accompanied by VHF radiation. We have also found that the pulse amplitudes in E‐change data and in LogRF data are not correlated.…”

“…Taking into account the results of Marshall et al (), who studied the first one or two classical IB pulses in two CG flashes and two intra‐cloud (IC) flashes and found significant VHF pulses occurring within the duration of each IB pulse, and findings of Kolmašová et al () who report that larger magnetic field IB pulses were systematically accompanied by VHF pulses in raw LMA (VHF) records, we first look for an occurrence of VHF pulses anytime within the duration of classical IB pulses. To be able to identify classical IB pulses, we downsampled the FA waveforms to 1 MHz to get rid of narrower pulses and subpulses.…”

“…Taking into account the results of Marshall et al (2019), who studied the first one or two classical IB pulses in two CG flashes and two intra-cloud (IC) flashes and found significant VHF pulses occurring within the duration of each IB pulse, and findings of Kolmašová et al (2018) who report that larger magnetic field IB pulses 10.1029/2019GL082488…”

“…Nevertheless, a correspondence of sources of impulsive VHF radiation detected by LMA (Lightning Mapping Array) systems with IB pulses seemed to be absent or very weak (Hare et al, 2017;Wilkes et al, 2016). A recent detailed analysis (Kolmašová et al, 2018) discovered that individual peaks of strong VHF radiation seen by separate LMA stations corresponded surprisingly well to the IB pulses. The analysis was limited by the performance of LMA stations that reported only the strongest VHF source within each 80-μs-long LMA window.…”

Physical Fields as Derivative of Deformation of Rock Massif and Technology of Their Monitoring

“…The physical and chemical bases of intermolecular links of rocks are at the same time precursors of the occurring disturbances of these links, the cause of which is an increase in stresses in the rocks and subsequent elastic or residual deformations. On the assumption of the basics of intermolecular links, it is obvious that electromagnetic fields are an indicator, since crystal lattice deformations cause a change in the distances between atoms and quantummechanical fluctuations of the electron density of particles (molecules, atoms) [12][13][14][15][16][17][18][19][20][21][22][23][24]. The instantaneous distribution of the electric charge of the molecule, which corresponds to the instantaneous dipole moment of the molecule (or a higher order multipole moment), induces an electric multipole moment in another molecule.…”