Thundercloud Project: Exploring high-energy phenomena in thundercloud and lightning

TL;DR

This study deployed a distributed sensor network in Japan to observe high-energy phenomena in thunderclouds, discovering photonuclear reactions and providing new insights into particle acceleration during thunderstorms.

Contribution

The paper introduces a novel ground-based sensor network for high-energy thundercloud observation and reports the first detection of photonuclear reactions in lightning.

Findings

Detected 51 gamma-ray events from thunderclouds and lightning

Discovered photonuclear reactions producing neutrons and positrons

Provided new insights into particle acceleration in thunderclouds

Abstract

We designed, developed, and deployed a distributed sensor network aiming at observing high-energy ionizing radiation, primarily gamma rays, from winter thunderclouds and lightning in coastal areas of Japan. Starting in 2015, we have installed, in total, more than 15 units of ground-based detector system in Ishikawa Prefecture and Niigata Prefecture, and accumulated 551 days of observation time in four winter seasons from late 2015 to early 2019. In this period, our system recorded 51 gamma-ray radiation events from thundercloud and lightning. Highlights of science results obtained from this unprecedented amount of data include the discovery of photonuclear reaction in lightning which produces neutrons and positrons along with gamma rays, and deeper insights into the life cycle of a particle-acceleration and gamma-ray-emitting region in a thundercloud. The present paper reviews objective, methodology, and results of our experiment, with a stress on its instrumentation.