Atmospheric Electric Discharges and Gamma-Ray Phenomena

Thunderstorms host a rich variety of electrical discharges that span time-scales from microseconds to minutes and produce radiation extending from radio waves up to high-energy gamma rays. Intense electric fields within thunderclouds can accelerate free electrons to relativistic speeds, leading to cascades of secondary particles and the emission of bremsstrahlung photons. These processes manifest as transient luminous events (TLEs) above storm tops, terrestrial gamma-ray flashes (TGFs) observed by satellites, minute-long gamma-ray glows at aircraft altitude, and thunderstorm ground enhancements (TGEs) recorded at mountain observatories. Such phenomena not only probe the fundamental physics of runaway electron avalanches and feedback mechanisms but also bear on atmospheric chemistry, ionisation of the middle atmosphere, and radiation exposure to aviation. Advances in ground-based networks, airborne detectors and space missions have begun to reveal the global distribution of high-energy atmospheric discharges and their interplay with cosmic rays and lightning initiation.

Research from Nature Portfolio

Recent studies have demonstrated a direct connection between prolonged gamma-ray glows and the onset of downward TGFs. Ground-based observations captured a gamma-ray glow that abruptly terminated in synchrony with a lightning discharge, while simultaneous detection of secondary photonuclear signatures confirmed the involvement of relativistic runaway electrons. In parallel, airborne measurements of long-duration glows near the thundercloud tops have quantified discharge currents sufficient to influence storm electrification, suggesting that electron avalanches compete directly with classical lightning channels. Complementary work has elucidated how bursts of high-energy electrons arising from run-away avalanches can trigger the first atmospheric discharges by locally increasing ionisation, thereby assisting in the initiation of cloud-to-ground lightning.

Atmospheric Electric Discharges and Gamma-Ray Phenomena publication trend

The graph below shows the total number of articles in atmospheric electric discharges and gamma-ray phenomena across all publications each year (not limited to Nature Index journals).

Technical terms

Relativistic Runaway Electron Avalanche (RREA): The process by which seed electrons in strong electric fields gain energy faster than they lose it, generating exponential growth of high-energy electrons.
Terrestrial Gamma-ray Flash (TGF): A sub-millisecond burst of gamma rays produced during the most intense phase of a lightning discharge.
Transient Luminous Event (TLE): Optical phenomena above thunderstorms, including sprites and elves, resulting from lightning-driven electromagnetic pulses.
Thunderstorm Ground Enhancement (TGE): A temporary increase in secondary cosmic-ray flux at ground level due to local atmospheric electron acceleration.
Bremsstrahlung: Radiation emitted when high-energy electrons are decelerated in the electric fields of atomic nuclei.
Extensive Air Shower (EAS): A cascade of secondary particles initiated by a high-energy cosmic ray or photon entering the atmosphere.

References

1. Overestimation of Astrophysical Gamma-Ray Energies during Thunderstorms: Synergy of Galactic and Atmospheric Accelerators. The Astrophysical Journal Letters (2024).
2. Relativistic electron avalanches as a thunderstorm discharge competing with lightning. Nature Communications (2015).
3. Gamma-ray glow preceding downward terrestrial gamma-ray flash. Communications Physics (2019).
4. Significant enhancements of secondary cosmic rays and electric field at the high mountain peak of Lomnický Štít in High Tatras during thunderstorms. Earth, Planets and Space (2020).
5. On the initiation of lightning in thunderclouds. Scientific Reports (2017).
6. Catalog of gamma-ray glows during four winter seasons in Japan. Physical Review Research (2021).
7. Simultaneous Observations of EIP, TGF, Elve, and Optical Lightning. Journal of Geophysical Research: Atmospheres (2021).