This paper reports a study to understand the radio spectrum of thunderstorm narrow bipolar events (NBEs) or compact intracloud discharges, which are powerful sources of high‐frequency (HF) and very high frequency (VHF) electromagnetic radiation. The radio spectra from 10 kHz to about 100 MHz are obtained for three NBEs, including one caused by fast positive breakdown and two by fast negative breakdown. The results indicate that the two polarities of fast breakdown have similar spectra, with a relatively flat spectrum in the HF and VHF band. The ratio of energy spectral densities in the very low frequency and HF bands is (0.9–5) × 105. We develop a statistical modeling approach to investigate if a system of streamers can explain the main features of fast breakdown. Assuming that the current moment peak and charge moment change of individual streamers vary in the ranges of 5–10 A‐m and 5–20 μC‐m, respectively, the modeling results indicate that a system of 107–108streamers can reproduce the current moment, charge transfer, and radio spectrum of fast breakdown. The rapid current variation on a time scale of nanoseconds required for fast breakdown to produce strong HF/VHF emissions is provided by exponentially accelerating and expanding streamers. Our study therefore supports the hypothesis that fast breakdown is a system of streamers. Finally, suggestions are given regarding future streamer simulations and NBE measurements in order to further develop our understanding of NBEs and lightning initiation.
The Deployable Low‐Band Ionosphere and Transient Experiment (DLITE) is a four‐element interferometric radio telescope made from mostly commercial off‐the‐shelf parts to minimize costs and maximize ease of deployment. It operates in the high frequency and very high frequency (VHF) regimes, nominally in a 30–40 MHz band, but with good sensitivity (sky‐noise dominated) in the 20–80 MHz range. Its configuration is optimized to probe ionospheric structure using the so‐called “A‐Team,” exceptionally bright sources of cosmic radio emission. Methods have been developed to track the apparent positions and intensities of A‐Team sources without the need for beam forming to enable measurements of VHF scintillations as well as total electron content gradients. Time difference of arrival and frequency difference of arrival methods have been adapted for all‐sky imaging to facilitate both statistical measurements of scintillation levels and time domain astronomy. This study provides a detailed description of the system design, the analysis algorithms, and the science that can be conducted using results from two prototype DLITE systems in Maryland and New Mexico.
more » « less- NSF-PAR ID:
- 10365275
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Radio Science
- Volume:
- 56
- Issue:
- 7
- ISSN:
- 0048-6604
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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