Recently, Postdoctoral Fellow Yang Qingliu from Professor He Jinliang's team in the Department of Electrical Engineering, in collaboration with researchers from Gifu University in Japan and the University of California, Santa Cruz in the United States, made new progress in research on lightning physics and high-energy atmospheric processes. Using a broadband interferometer, the research team performed sub-microsecond time-resolution imaging of the initial leaders of two Energetic Compact Strokes (ECS), systematically observing for the first time a series of Fast Positive Breakdowns (FPB) and Fast Negative Breakdowns (FNB) in ECS initial leaders, revealing the fine discharge characteristics in the formation process of this special type of intense lightning.

The related research results, entitled "Fast Breakdowns Observed in the Initial Leaders of Two Energetic Compact Strokes," were published in Geophysical Research Letters (GRL), an important international journal in the field of lightning physics.

From Intense Lightning to High-Energy Gamma Rays

Terrestrial Gamma-ray Flashes (TGFs) are a type of high-energy radiation phenomenon produced in thunderstorms, and their formation mechanism is an important scientific question in current research on atmospheric electricity and high-energy atmospheric physics.

In recent years, studies have found that a special type of intense negative cloud-to-ground return stroke—the Energetic Compact Stroke (ECS)—exists in winter thunderstorms in Japan. This type of discharge has an extremely large return stroke current and is closely related to downward TGFs. Before an ECS Ccurs, there is usually a fast downward initial leader with a speed far higher than that of ordinary negative leaders, but how this high-speed leader forms has previously lacked fine-scale observation.

The research team combined broadband interferometer and high- and low-frequency lightning location observations to analyze two ECS events that produced downward TGFs. Both initial leaders began to develop rapidly downward from a low altitude of about 1 km above the ground and eventually formed strong return strokes with peak currents of about −260 kA and −170 kA, followed by the observation of downward TGFs in each case.

[Figure 1. The process of ECS development from initial leader to strong return stroke and TGF Ccurrence]

[Video 1] The complete two-dimensional discharge evolution process of the lightning in which ECS leader B was located, showing the spatiotemporal development of the lightning channel within about 476 ms.

Broadband Interferometer Reveals Fast Breakdowns Inside High-Speed Leaders

Further magnifying the observations to the microsecond scale revealed that the seemingly continuous downward development of the ECS initial leader actually contains a series of discrete fast breakdown processes.

Broadband interferometric imaging also showed that these fast breakdowns formed obvious multi-branched discharge structures, with more than half of the fast negative breakdowns propagating approximately in the vertical direction. At the same time, each fast breakdown could be matched to a corresponding low-frequency electric field change pulse, indicating that fast breakdowns may be an important component of the rapid development process of ECS initial leaders.

Providing New Observations for Understanding the Link Between Intense Lightning and High-Energy Radiation

This study reveals for the first time, at the sub-microsecond scale, the spatiotemporal evolution characteristics of a series of fast breakdowns inside ECS initial leaders, extending research on fast breakdowns from the very initial stage of lightning to the development process of the complete initial leader, and providing new observational evidence for further understanding the potential physical links among fast breakdowns, intense lightning return strokes, and terrestrial gamma-ray flashes.

Paper information:

Qingliu Yang, Daohong Wang, Ting Wu, David M. Smith, Yuki Hamajima, Jinliang He. Fast Breakdowns Observed in the Initial Leaders of Two Energetic Compact Strokes. Geophysical Research Letters, 2026.

Fast Breakdowns Observed in the Initial Leaders of Two Energetic Compact Strokes - Yang - 2026 - Geophysical Research Letters - Wiley Online Library