Multi‐Stroke Positive Cloud‐To‐Ground Lightning Sharing the Same Channel Observed With a VHF Broadband Interferometer

• Published in: Geophysical research letters Vol. 49; no. 9
• Main Authors: Urbani, M., Montanyá, J., Velde, O. A., Arcanjo, M., López, J. A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-05-2022
• Subjects: Arrays; Broadband; Charge transfer; Clouds; High frequency; Interferometers; Lightning; Lightning flashes; Mapping; Polarity; positive cloud‐to‐ground lightning; Return stroke; Return strokes (lightning); Spatial discrimination; Spatial resolution; Very high frequencies; VHF broadband interferometer
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097272

This work presents the first observation of a multi‐stroke positive cloud‐to‐ground lightning flash sharing the same channel to ground mapped with a very high frequency broadband interferometer and a Lightning Mapping Array. This type of lightning flash is very rarely observed, and it is currently unclear how frequent it is and even under what conditions it occurs. Our observations indicate a scenario where the first downward positive leader initiates from a decayed negative channel. After the first return stroke, some of the main negative channel branches stop propagating and are likely cut off. A fast recoil leader and/or a fast breakdown play a crucial role in reconnecting these previously decayed leader channels and initiating the subsequent positive stroke. The mechanism we propose to describe the phenomenon allows us to explain its rarity and the discrete positive charge transfer to the ground.
Plain Language Summary
In the same lightning flash, whose usual duration is less than a second, there can be multiple negative cloud‐to‐ground strokes with different terminations or following a preexisting channel to the ground. In contrast, it is not common to have multiple positive cloud‐to‐ground (+CG) strokes, and especially multi‐stroke +CG flashes sharing the same channel to ground are very rarely observed. This polarity asymmetry is not well understood and many aspects are debated. In this letter, we present for the first time a very high frequency (VHF) radio band observation of a multi‐stroke +CG flash along the same channel, observed simultaneously by a VHF broadband interferometer and a Lightning Mapping Array in north‐central Colombia. These combined observations have unprecedented temporal and spatial resolution and allowed us to observe in detail the development of the flash and especially to understand the initiation mechanism of the subsequent positive stroke.
Key Points
First time observation of positive cloud‐to‐ground strokes sharing the same channel to ground with a very high frequency (VHF) broadband interferometer
A fast recoil leader and/or a fast breakdown connecting decayed leader channels play a crucial role in triggering the subsequent positive stroke
The high‐resolution comparison between the first and subsequent stroke shows different VHF signatures related to the channel conductivity