| 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 (2023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 |
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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 reported period, my main focus was on estimating the electron density profile using the frequency residual data obtained from the Radio Science (RS) payloads onboard the Venus Express (VEX) and Akatsuki missions around Venus. I obtained a total of 110 electron density profiles from VEX-RS observations and also completed the analysis for Akatsuki RS observations as well. These profiles were carefully examined, particularly looking for instances of enhanced electron density at lower altitudes (around 110 km).
In line with the project's objectives, we investigated the influence of space weather events on the sporadic occurrence of the V0 layer. Specifically, we explored the potential impact of Solar Energetic Particles (SEPs) on this layer. Apart from RS experiments, we utilized background data from the Electron Spectrometer (ELS) on ASPERA-4 aboard VEX to identify SEP events during VEX-RS observations. We also examined observations from the Space Environment Monitor (SEM) suite aboard the Geostationary Operational Environmental Satellite (GOES) during alignments of Venus, Earth, and the Sun to confirm SEP events during Akatsuki-RS observations. Our thorough analysis indicates that while SEPs are considered, they may not be the primary driver behind the formation of the V0 layer in the Venusian ionosphere.
This study has been submitted to a peer-reviewed journal for potential publication.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
1. I focused on analyzing the Radio Science experiments conducted by Akatsuki mission, resulting in the acquisition of corresponding electron density profiles. Additionally, I adapted my software to encompass the analysis of the VEX-RS dataset, utilizing frequency residuals to retrieve electron density profiles. By combining data from both missions, I obtained a total of 154 electron density profiles. Among these observations, approximately 23% revealed the occurrence of the V0 layer. While significant progress has been made, around 60% of data processing to retrieve electron density has been accomplished.
2. Solar Energetic Particles (SEPs) were speculated as a potential source for the production of the V0 layer. I delved into the possible role of SEPs in the formation of the V0 layer. I utilized electron density profiles from radio occultation conducted by the VEX and Akatsuki missions. To identify SEP events, I used background data from the Electron Spectrometer (ELS) on ASPERA-4 aboard the VEX mission. Additionally, observations from the Space Environment Monitor (SEM) suite aboard the Geostationary Operational Environmental Satellite (GOES) during alignments of Venus, Earth, and the Sun were also examined. Our comprehensive analysis suggests that while SEPs are considered, they may not serve as the primary driver behind the formation of the V0 layer in the Venusian ionosphere.
3. I presented a research paper at the AGU Fall meeting in December 2023. Additionally, I shared a detailed outcomes concerning the Venusian ionosphere at the Akatsuki Science Working Team meeting.
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| 今後の研究の推進方策 |
The future work plan can be oulined as follow: (1) Develop another software to analyze the raw data obtained from the Radio Science (RS) experiments conducted by the Pioneer Venus Orbiter (PVO) mission. Retrieve electron density profiles along with other atmospheric parameters such as temperature, pressure, and number density profiles of the lower atmosphere. (2) Investigate the origin of the V0 layer in the Venusian ionosphere. The detailed data analysis has suggested that the V0 layer may be a permanent feature of the Venusian ionosphere. Further scrutiny of the data is planned to delve into this phenomenon in more detail. (3) Develop a comprehensive software tool to retrieve sulfuric acid profiles using Akatsuki-RS observations in the Venusian atmosphere. Additionally, explore the coupling mechanisms between the lower atmosphere and ionosphere. (4) 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. (5) I also plan to attend scientific conferences scheduled for this fiscal year, such as the Japan Geoscience Union (JpGU) Meeting-2024, Asia Oceania Geoscience Society (AOGS) annual meetings, Committee on Space Research (COSPAR), and AGU Fall meeting in 2024, to present the scientific outcomes to the broader scientific community.
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