| 研究課題/領域番号 |
23KF0196
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| 研究種目 |
特別研究員奨励費
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| 配分区分 | 基金 |
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| 応募区分 | 外国 |
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| 審査区分 |
小区分17010:宇宙惑星科学関連
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| 研究機関 | 東京大学 |
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研究代表者 |
今村 剛 東京大学, 大学院新領域創成科学研究科, 教授 (40311170)
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| 研究分担者 |
TRIPATHI KESHAV 東京大学, 大学院新領域創成科学研究科, 外国人特別研究員
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| 研究期間 (年度) |
2023-11-15 – 2026-03-31
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| 研究課題ステータス |
交付 (2024年度)
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| 配分額 *注記 |
2,100千円 (直接経費: 2,100千円)
2025年度: 800千円 (直接経費: 800千円)
2024年度: 1,000千円 (直接経費: 1,000千円)
2023年度: 300千円 (直接経費: 300千円)
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| キーワード | Radio Science / Akatsuki & Venus Express / Venusian Ionosphere / V0 Layer / Space weather events / SEP impact on V0 layer / ICME impact on V0 layer / Akatsuki / Venus Express / Venusian ionosphere / Space weather |
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| 研究開始時の研究の概要 |
金星の電離圏に関連する未解決の問題に取り組む。とくに以下の目標を達成することを目指す。(1) 異なる高度に現れる異なる層の特徴を解明し、金星の電離圏の形成に関与する基本的なメカニズムを特定すること。(2) 太陽風粒子と金星の電離圏上部との相互作用を理解し、大気イオンと高エネルギー中性粒子の散逸を支配する物理過程を探求すること。これらの目的のために、過去のミッションで記録された電波掩蔽データの解析を行う。異なる地球物理学的条件や太陽活動条件下で、金星の電離圏に関する数百の電子密度プロファイルを得る。得られた電子密度プロファイルを検討し、各種イオン層の形成に関する理論を提案する。
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| 研究実績の概要 |
During the reporting period, our research focused on understanding the formation of a newly observed plasma layer (V0 layer) in the lower Venusian ionosphere, identified through radio science experiments conducted by Akatsuki and Venus Express. This layer, believed to be sporadic in nature, remains a key open question in Venus aeronomy.
1. We investigated the potential role of space weather, specifically Solar Energetic Particles (SEPs) in the formation of the V0 layer. SEP events were identified using the ELS instrument on VEX and the SEM suite on GOES during Earth-Venus-Sun alignments. Our analysis indicates that while SEPs may contribute, they are unlikely to be the primary driver. This work has been published in a peer-reviewed journal.
2. A reanalysis of Akatsuki’s single-frequency radio occultation data revealed that the detectability of the V0 layer is sensitive to the retrieval technique used.
3. We observed significant solar zenith angle variation along the ray path, challenging the common assumption of spherical symmetry in electron density retrieval. To address this, we developed a new algorithm that accounts for plasma asymmetry along the ray path, enabling more accurate density estimation. This work has been submitted for peer-reviewed publication.
4. Additional analysis suggests a possible enhancement in neutral temperature in regions where plasma layers are present.
5. Other than Venus, discover a high plasma density trapped by crystal magnetic field in the lunar environment when it was inside the Earth’s geotail region.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
(1) Development of a Temperature Retrieval Algorithm: A new method is being developed to derive the temperature profile of Venus’s neutral atmosphere up to 110 km altitude. This approach assumes that the radio signal is primarily influenced by the neutral atmosphere below this altitude and applies the hydrostatic equilibrium condition to retrieve temperature values.
(2) Impact of ICMEs on Ionospheric Structure: Ongoing analysis is focused on investigating the influence of Interplanetary Coronal Mass Ejection (ICME) events on electron density profiles, particularly during the daytime and in the upper regions of the ionosphere. The study also examines the potential role of ICMEs in the formation of the V0 layer on the nightside of Venus.
(3) Nighttime Ionosphere Retrieval: Electron density profiles for the nightside ionosphere are being retrieved using Akatsuki radio science data to improve understanding of ionospheric behavior under low solar illumination.
(4) Detection of Surface Wave Signatures: A software tool is under development to identify surface wave features in electron density profiles above the primary peak. This analysis aims to detect the possible presence of gravity waves in the upper ionosphere and assess their impact on ionospheric dynamics.
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| 今後の研究の推進方策 |
The proposed research aims to advance our understanding of the structure and dynamics of planetary ionospheres, with a primary focus on Venus. By leveraging radio occultation (RO) data from past and ongoing missions (Venus Express, Akatsuki), this will address key open questions regarding ionospheric variability, plasma-neutral coupling, and atmospheric wave propagation.
(1) Temperature Retrieval in the Lower Atmosphere-Ionosphere Coupling Region: Develop and validate a novel retrieval algorithm to estimate the neutral temperature profile of Venus up to 110 km altitude. Observe the temporal variation of the temperature in the coupling region and its role on the dtection of the V0 layer.
(2) Previous studies have reported a surface wave-like structure in the V3 layer of the Venusian ionosphere. Speculations regarding the role of interplanetary magnetic field lines in creating such perturbations exist. However, I intend to investigate the possibility of vertical propagation of gravity waves up to the V3 region, generated in the lower atmosphere, and observe their impact.
(3) Assessing Space Weather Impacts on Ionospheric Structure: Retrieve the electron density profile for the night side based on the single frequency Akatsuki observation to observe the role of ICME events on the formation of the V0 Layer.
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