Studies on electron acceleration and multiplication in lightning by a ground-based array of small dosimeters

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K22354
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0203:Particle-, nuclear-, astro-physics, and related fields
• Research Institution: Osaka University (2021); Institute of Physical and Chemical Research (2020)
• Principal Investigator: WADA YUUKI 大阪大学, 工学研究科, 助教 (40879144)
• Project Period (FY): 2020-09-11 – 2022-03-31
• Keywords: 地球ガンマ線フラッシュ / 雷放電 / 電場加速 / 雷雲 / 高エネルギー大気現象 / 放射線

Outline of Final Research Achievements

Thunderclouds and lightning discharges are know to sometimes cause high-energy atmospheric phenomena. Terrestrial gamma-ray flashes (TGFs) are an instantaneous gamma-ray emission of several hundred microseconds synchronized with a lightning discharge, a phenomenon in which electrons are accelerated and multiplied to relativistic energies by lightning discharges. However, the mechanism of electron acceleration and multiplication in a dense atmosphere has not yet been clarified. In this work, we developed a small detector for ground-based observation of TGFs focusing on winter thunderstorms in the Hokuriku region, and succeeded in observing a TGF. In addition, by comparing TGFs and broadband low-frequency radio observations, we clarified what types of lightning discharges can trigger TGFs, and obtained a suggestion for the mechanism of electron acceleration and multiplication.

Free Research Field

高エネルギー大気物理学

Academic Significance and Societal Importance of the Research Achievements

TGFは雷放電の初期で発生しており、発生や進展のメカニズムが未だよく理解されていない雷放電に対し、TGFがどのような影響を与えるか、といった点も今後の研究として期待される。またTGFでは大量のガンマ線が発生することから、特に航空機で飛行中に直撃した場合に乗客・乗員の被ばく量が懸念される。現在ではどのような雷でTGFが起きているか解明されていないものの、本研究でその手がかりが得られており、将来的な被ばく量推定に役立つと考えられる。