We report a new approach to measure indirectly the ambient thunderstorm electric fields in fast positive breakdown regions. For a given geometry of the discharged fast breakdown region, we show that there is a minimum ambient electric field required to produce a given charge moment change. We apply this approach to the fast breakdown measurements for two events reported by Rison et al. (2016,
This paper exploits triggered lightning as a point source for the basin‐scale electromagnetic tomographic survey to image 3‐D subsurface electrical properties in basins. This paper further develops a new temporal moment approach, overcoming the difficulties in forward and inverse modeling of 3‐D Maxwell’s equations with heterogeneous parameter fields. Using this approach, we find that the influence of a single triggered lightning strike covers a radius of 20–70 km with detectable signals. The cross‐correlation analysis between the moment difference of the electric and electric/magnetic property field indicates that the approach is suitable for mapping subsurface electric conductivity (
- NSF-PAR ID:
- 10383709
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 23
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract https://doi.org/10.1038/ncomms10721 ) and find that the average ambient electric field in the discharged region is at leastV/m at the 9.5 km initiation altitude of these events. This electric field is close to the runaway electron avalanche electric field and to the critical field for positive streamer propagation. These measurements provide a meaningful starting point for more detailed analyses or simulations of what occurs inside the fast breakdown process that is responsible for the initiation of at least some lightning discharges. -
Abstract Electric fields associated with a developing natural lightning leader are difficult to measure. This work demonstrates a new approach to indirectly probing the electric fields in the streamer zone of a lightning leader. Using a 10–250 MHz broadband lightning interferometer, very high frequency (VHF) radio emissions from the tip of a positive cloud‐to‐ground (CG) leader were measured and localized. We specially use a normalized spectral analysis to avoid the challenge of absolute system calibration to show that the positive leader spectrum exhibits a clear cutoff frequency at 80 MHz. Compared with theoretical predictions, this cutoff frequency corresponds to a streamer growth rate of
and an average electric field of 0.9 times the conventional breakdown field in streamer bursts from the positive leader. Implications for the detectability of positive leaders through VHF emissions and for the production of X‐rays by positive leaders are analyzed. -
Abstract Fast breakdown (FB), a breakdown process composed of systems of high‐velocity streamers, has been observed to precede lightning leader formation and play a critical role in lightning initiation. Vigorous FB events are responsible for the most powerful natural radio emissions on Earth, known as narrow bipolar events (NBEs). In this paper, an improved version of the Griffiths and Phelps (1976,
https://doi.org/10.1029/jc081i021p03671 ) model of streamer breakdown is used alongside supervised machine learning techniques to probe the required electric fields and potentials inside thunderstorms to produce FB and NBEs. Our results show that the electrostatic conditions needed to produceFB observed in New Mexico at 9 km altitude and FB in Florida at 14 km altitude are about the same, each requiring about 100 MV potential difference to propagate 500 m. Additionally, the model illustrates how electric field enhancement ahead of propagating FB can initiate rebounding FB of the opposite polarity. -
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