Observation of long burst thundercloud gamma rays and their origin by a meteorological radiosonde

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K03667
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
• Research Institution: The University of Tokyo
• Principal Investigator: Minowa Makoto 東京大学, 大学院理学系研究科(理学部), 名誉教授 (90126178)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 雷 / ガンマ線 / ラジオゾンデ

Outline of Final Research Achievements

A meteorological radiosonde equipped with a detector capable of discriminating electrons and gamma rays was directly injected into thunderclouds to directly detect the vertical high-intensity electron flux with energy of the order of 10 MeV, which is considered to be the origin of long-burst thundercloud gamma rays. A total of six radiosonde flights were made in Kashiwa City, Chiba Prefecture, and Wajima City, Ishikawa Prefecture, and charged particle counting data were successfully collected as a function of altitude.
However, none of them were able to directly detect the high-intensity electron flux in thunderclouds because they could not be deployed near the center of sufficiently strong thunderclouds. This is very regrettable, although it is unavoidable because we are targeting an unstable meteorological phenomenon.

Free Research Field

宇宙素粒子物理学

Academic Significance and Societal Importance of the Research Achievements

これまで未知であった雷雲中での静電電子加速現象と電子なだれによる増倍現象の存在を実証し、ロングバースト雷雲ガンマ線の起源を確定することができていれば、通常の宇宙線以外に、これまで知られていなかった別種の強力な自然放射線が地上に振り注いでいる機構を明らかにでき、宇宙線物理学と地球物理学の両方に重要な知的メリットを与えるものであった。
しかし、ラジオゾンデを十分強い雷雲の中心付近に投入することはできず、大強度電子フラックスを直接検出することはできなかった。大変残念である。