Propagation Effects of Slanted Narrow Bipolar Events: A Rebounding‐Wave Model Study

• Published in: Journal of geophysical research. Atmospheres 2024-07, Vol.129 (14), p.n/a
• Main Authors: Li, Dongshuai, Luque, Alejandro, Rachidi, Farhad, Rubinstein, Marcos, Neubert, Torsten, Zhu, Yanan, Chanrion, Olivier, Silva, Caitano, Krehbiel, Paul R.
• Format: Article
• Language: English
• Subjects: Amplitudes; Electric fields; Electromagnetic fields; Electromagnetic induction; Electromagnetism; Electrostatic properties; finite‐difference time‐domain (FDTD); Firing pattern; Inclination; Intracloud discharges; Lightning; Lightning flashes; Modelling; narrow bipolar events (NBEs); Orientation effects; Radiation; Radiation measurement; slanted effect; Thunderstorms; transmission line model; Transmission lines; Vertical orientation; Wave propagation; Waveforms; Weather
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2023JD040497

Narrow bipolar events (NBEs) are impulsive and powerful intracloud discharges. Recent observations indicate that some NBEs exhibit a slanted orientation rather than strictly vertical. This paper investigates the effect of the slanted NBEs using a newly developed rebounding‐wave model. The modeling results are validated against the full‐wave Finite‐ Difference Time‐Domain method and compared with measurements for both vertical and slanted NBE cases. It is found that the inclination of the NBEs affects both the waveforms and amplitudes of the electrostatic, induction and radiation components of the electric fields at close distances (≤10 km). However, it primarily influences the amplitudes of the fields for distances beyond 50 km, where the radiation component dominates, resulting in changes of ≥30% when the slant angle exceeds 30°. The slanted rebounding‐wave model improves the agreement with respect to a purely vertical channel and can be extended to any discharge geometry at arbitrary observation distances. Plain Language Summary Narrow Bipolar Events (NBEs) are unique intracloud discharges that occur either individually or as the initiation event for lightning flashes inside thunderstorms. Knowing the physical mechanisms of NBEs will help us to better understand how lightning initiates inside thunderstorms. Recent studies indicated that NBEs could exhibit a slanted orientation rather than being strictly vertical. However, the inclination of NBEs has not been considered in previous transmission line models, leading to uncertainty when evaluating their characteristics based on electromagnetic fields. Here, in the light of recent observations, we analyze the propagation effect of the slanted NBEs by using a newly developed slanted rebounding‐wave model, and we compare the modeling results with observations. This study contributes to a better understanding of the physical mechanism of NBEs and provides a reference for accurately characterizing NBEs based on their electromagnetic fields. Key Points The propagation effect of slanted Narrow bipolar events (NBEs) at different distance is investigated and compared with the observations The inclination of the NBEs could significantly affect the electromagnetic fields in the close distance The proposed equations will improve the quality of inferred features of slanted NBEs and can be extended to any discharge shape