Downward terrestrial gamma-ray flash associated with collision of lightning leaders

Area of Science:

• Atmospheric Physics
• High-Energy Astrophysics
• Electromagnetism

Background:

• Terrestrial gamma-ray flashes (TGFs) are intense bursts of gamma rays from thunderstorms.
• The precise mechanism for generating the vast number of relativistic electrons required for TGFs in dense atmospheres remains unclear.
• Lightning involves complex leader propagation and leader-leader interactions.

Purpose of the Study:

• To investigate the origin of relativistic electrons during terrestrial gamma-ray flashes (TGFs).
• To understand the relationship between leader interactions and TGF initiation.
• To elucidate the atmospheric conditions conducive to TGF production.

Main Methods:

• Utilized ground-based observations combining optical, radio frequency, and high-energy detectors.
• Focused measurements on television transmission towers during a lightning event.
• Correlated TGF occurrence with a specific cloud-to-ground discharge and leader activity.

Main Results:

• A TGF event was observed concurrently with a -56 kA cloud-to-ground discharge.
• The TGF initiated approximately 30 microseconds before the main cloud-to-ground current, coinciding with leader approach.
• The data suggests a strong, compact electric field formed between colliding leaders, accelerating electrons to relativistic energies.

Conclusions:

• The interaction between downward negative and upward positive leaders provides the necessary conditions for TGF generation.
• A strong electric field localized between approaching leaders is the source of relativistic electron acceleration.
• This finding clarifies a key aspect of high-energy phenomena in thunderstorms.