Numerical simulations of compact intracloud discharges as the Relativistic Runaway Electron Avalanche‐Extensive Air Shower process

Abstract

[1] Compact intracloud discharges (CIDs) are sources of the powerful, often isolated radio pulses emitted by thunderstorms. The VLF-LF radio pulses are called narrow bipolar pulses (NBPs). It is still not clear how CIDs are produced, but two categories of theoretical models that have previously been considered are the Transmission Line (TL) model and the Relativistic Runaway Electron Avalanche-Extensive Air Showers (RREA-EAS) model. In this paper, we perform numerical calculations of RREA-EASs for various electric field configurations inside thunderstorms. The results of these calculations are compared to results from the other models and to the experimental data. Our analysis shows that different theoretical models predict different fundamental characteristics for CIDs. Therefore, many previously published properties of CIDs are highly model dependent. This is because of the fact that measurements of the radiation field usually provide information about the current moment of the source, and different physical models with different discharge currents could have the same current moment. We have also found that although the RREA-EAS model could explain the current moments of CIDs, the required electric fields in the thundercloud are rather large and may not be realistic. Furthermore, the production of NBPs from RREA-EAS requires very energetic primary cosmic ray particles, not observed in nature. If such ultrahigh-energy particles were responsible for NBPs, then they should be far less frequent than is actually observed.

Physical mechanism of initial breakdown pulses and narrow bipolar events in lightning discharges

“…Figure shows simulated two‐station E field waveform as observed by Eack []. This (referred hereafter and in Table as NBE‐1) observation was used in a number of papers in existing literature for model validation purposes [ Watson and Marshall , ; Nag and Rakov , ; Arabshahi et al , ]. A +NBE in our model is generated in Region B of the thunderstorm (see Figure ) by the first upward step of the negative leader extremity, as schematically shown in Figure .…”

“…The first one is referred to as transmission line model and it was applied to make inferences about the sources of both IBP and NBE signatures [e.g., Shao and Heavner , ; Watson and Marshall , ; Nag and Rakov , ; Karunarathne et al , ]. The second one is based on the assumption that relativistic runaway electron avalanches seeded by cosmic ray air showers are the source of NBEs [e.g., Gurevich et al , , ; Gurevich and Zybin , ; Tierney et al , ; Arabshahi et al , ]. Having obtained the current distribution I ( z , t ) using either modeling strategy, the electric field generated by these sources can be calculated and compared to measurements.…”

“…Its electromagnetic radiation would have a characteristic bipolar waveform, similar to NBEs. However, as suggested by Dwyer and Uman [, section 6.5] and further quantified by Arabshahi et al [], the required thunderstorm and EAS properties to match observed NBE waveforms appear to be unrealistic. For instance, Arabshahi et al [] demonstrated that the required minimum cosmic ray energy to reproduce measured NBEs through the EAS–RREA model is ∼10 21 eV.…”

“…However, as suggested by Dwyer and Uman [, section 6.5] and further quantified by Arabshahi et al [], the required thunderstorm and EAS properties to match observed NBE waveforms appear to be unrealistic. For instance, Arabshahi et al [] demonstrated that the required minimum cosmic ray energy to reproduce measured NBEs through the EAS–RREA model is ∼10 21 eV. These authors estimate that the frequency of occurrence of an EAS with such high energy, over a typical thunderstorm area of 100 km 2 , is 1 every 67 years.…”

Electrostatic field changes and durations of narrow bipolar events

“…Arabshahi et al . [] stated that their RREA‐EAS model of NBEs was only able to match measured NBE waveforms by using thunderstorm electric fields and cosmic ray energies that were not realistic. In a recent paper (published while this paper was under review), Rison et al .…”