Abstract
AbstractWe have designed, developed, and deployed a distributed sensor network to observe high-energy ionizing radiation, primarily gamma rays, from winter thunderclouds and lightning in coastal areas of Japan. Starting in 2015, we have installed a total of more than 15 ground-based detector systems 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 the 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 the objective, methodology, and results of our experiment, with an emphasis on its instrumentation.
Highlights
Lightning discharges and thunderclouds have been known as electrical phenomena in the atmosphere since the discovery by Benjamin Franklin in 1752
Wilson’s runaway electron scheme was developed with multiplication processes into relativistic runaway electron avalanches (RREA) by Gurevich et al [2]; secondary electrons produced by accelerated electrons via ionization loss processes become seed electrons and are accelerated in electron fields
Detector-control and data-acquisition subsystem We developed a data-acquisition and detector-control system based on (1) an analog front-end board, (2) a digital signal-processing (DSP) board, and (3) a commercial-off-the-shelf single-board computer
Summary
Lightning discharges and thunderclouds have been known as electrical phenomena in the atmosphere since the discovery by Benjamin Franklin in 1752. Torii et al [21] reported gamma-ray glows lasting for ∼1 minute during winter thunderstorms for the first time, recorded by dosimeters installed at a nuclear power facility in a coastal area of the Sea of Japan. Another measurement with multiple dosimeters succeeded in tracking a gamma-ray glow moving with a thundercloud and ambient wind flow [22]. The GROWTH experiment is a ground-based measurement of gamma rays and high-energy particles aimed at detecting and exploring high-energy atmospheric phenomena during winter thunderstorms in Japan. When we put a stress on the timescale of gamma-ray burst events from the observational point of view, we call minute-lasting gamma-ray glow a “long-duration gamma-ray burst.”
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