Application of QZSS-TEC for seismology, volcanology, and upper atmospheric physics

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K04120
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Hokkaido University
• Principal Investigator: Heki Kosuke 北海道大学, 理学研究院, 名誉教授 (30280564)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 準天頂衛星 / GNSS-TEC / 電離圏擾乱 / 火山噴火 / 大気モード / 福徳岡の場 / トンガ海底火山

Outline of Final Research Achievements

Unlike GNSS (Global Navigation Satellite System) satellites with conventional half-day period orbits, QZSS is composed of 3 satellites having quasi-zenith orbits, staying around local zenith for 1/3 day, and 1 geostationary orbit satellite. They are useful for studying ionospheric disturbances because their data do not suffer from changes due to apparent movement of satellites in the sky. Here, I studied ionospheric disturbances in terms of changes in ionospheric total electron contents (TEC) associated with recent earthquakes and volcanic eruptions using QZSS. Remarkable findings include the detection of atmospheric modes with four different frequencies excited by the 2021 eruption of the Fukutoku-Okanoba submarine volcano. I also clarified the disturbances of ionoshere above Japanese Islands caused by multiple passages of the Lamb wave by the 2022 eruption of the Hunga-Tonga Hunga-Ha'apai submarine volcano.

Free Research Field

地球物理学

Academic Significance and Societal Importance of the Research Achievements

米国のGPSに代表される従来の衛星測位システムに加えて、わが国独自の測位衛星システムとして打ち上げられた準天頂衛星システム（QZSS）の、地球物理学的な有用性に注目した初めての研究であり、日本の科学行政に関わる社会的意義がある。またQZSS-TEC法を用いると衛星の見かけの動きに伴う変化に邪魔されずに純粋に電離圏の時間変化に注目できるが、その有用性が火山噴火に伴う大気モードの観測に明確に発揮されたこと。これは研究期間中に二度の大規模な海底火山の噴火が生じたという偶然に味方された側面が大きいが、火山噴火による大気擾乱のダイナミクスの一環を明らかにした学術的意義は大きい。