Observation of an energetic radiation burst from mountain-top thunderclouds

TL;DR

This study reports the first simultaneous detection of gamma rays and electrons from thunderclouds at a mountain observatory, revealing energetic radiation bursts associated with thunderclouds rather than lightning.

Contribution

It provides direct observational evidence of energetic radiation emissions from thunderclouds, including spectral analysis and source distance estimation.

Findings

Gamma rays extend up to 10 MeV.

Electrons likely originate from cloud acceleration regions.

Radiation source estimated 60-130 meters from detector.

Abstract

During thunderstorms on 2008 September 20, a simultaneous detection of gamma rays and electrons was made at a mountain observatory in Japan located 2770 m above sea level. Both emissions, lasting 90 seconds, were associated with thunderclouds rather than lightning. The photon spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung gamma rays arriving from a source which is 60 - 130 m in distance at 90% confidence level. The observed electrons are likely to be dominated by a primary population escaping from an acceleration region in the clouds.