Observational investigation for effects of the lightning discharges in South-east Asia on the D/E-region ionosphere

2015 Fiscal Year Final Research Report

• Project/Area Number: 25302005
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 海外学術
• Research Field: Space and upper atmospheric physics
• Research Institution: Chiba University
• Principal Investigator: Ohya Hiroyo 千葉大学, 工学(系)研究科(研究院), 助教 (00241943)
• Co-Investigator(Kenkyū-buntansha): TAKAHASHI Yukihiro 北海道大学, 大学院理学研究院, 教授 (50236329) ; TSUCHIYA Fuminori 東北大学, 大学院理学研究科, 助教 (10302077) ; YAMASHITA Kozo サレジオ工業高等専門学校, 電気工学科, 講師 (20609911)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 雷放電 / EMP / 下部電離圏 / VLF/LF帯電磁波

Outline of Final Research Achievements

During 2013-2015 physical years, we could install new VLF observation system in Philippines and Vietnam to reveal the effects of lightning discharges on the lower ionosphere. All the five observation stations of Asia VLF Observation Network (AVON) were completed. By analyzing the AVON data, the following results were obtained.
(1)　The phase change strongly depends in both strength of EMP and distance of causative lightning from the 1-hop point, if the strength of the EMP exceeds the breakdown electric field at 90 km altitude. (2) Outside of these distances, the phase decreases (which correspond to the ionization decrease) was found. Intensity of EMP degreases as distance from a causative lightning. When the electric filed strength becomes lower than the breakdown threshold, electron attachment rate dominates ionization rate, causing decrease in ionization. This suggests that EMP does not affect ionization state in the lower ionosphere just above lightning.

Free Research Field

電離圏