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Detection of high-energy gamma rays from winter thunderclouds
H Tsuchiya1, T Enoto, S Yamada
1Cosmic Radiation Laboratory, Riken, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
Physical Review Letters
|November 13, 2007
Summary
High-energy gamma-ray bursts were observed from thunderclouds before lightning strikes. This provides evidence that strong electric fields accelerate electrons to over 10 MeV within thunderclouds.
Area of Science:
- Atmospheric Physics
- High-Energy Astrophysics
- Electromagnetism
Background:
- Thunderstorms generate powerful electrical fields.
- Lightning is a dramatic electrical discharge within or between clouds or from a cloud to the ground.
- Previous research suggested high-energy phenomena in thunderclouds but lacked direct observational evidence.
Purpose of the Study:
- To report on the observation of burstlike gamma-ray emission from thunderclouds.
- To investigate the origin and characteristics of this emission.
- To provide evidence for high-energy electron acceleration in thunderclouds prior to lightning.
Main Methods:
- Ground-based observation of gamma-ray emissions during strong thunderstorms.
- Spectral analysis of the detected gamma-ray bursts.
- Correlation of gamma-ray emissions with subsequent cloud-to-ground lightning discharges.
Main Results:
- A 40-second burstlike gamma-ray emission was detected preceding cloud-to-ground lightning.
- The emission spectrum extended up to 10 MeV.
- The spectrum is consistent with bremsstrahlung photons from relativistic electrons.
Conclusions:
- Strong electric fields within thunderclouds can continuously accelerate electrons to energies exceeding 10 MeV.
- This observation offers the first clear evidence of such pre-lightning electron acceleration.
- The findings contribute to understanding the physics of lightning and related atmospheric phenomena.
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