| 研究課題/領域番号 |
22K14083
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| 研究種目 |
若手研究
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| 配分区分 | 基金 |
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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 | 名古屋大学 |
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研究代表者 |
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| 研究期間 (年度) |
2022-04-01 – 2025-03-31
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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 |
4,550千円 (直接経費: 3,500千円、間接経費: 1,050千円)
2024年度: 1,560千円 (直接経費: 1,200千円、間接経費: 360千円)
2023年度: 1,300千円 (直接経費: 1,000千円、間接経費: 300千円)
2022年度: 1,690千円 (直接経費: 1,300千円、間接経費: 390千円)
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| キーワード | VLF waves / conjugated events / bursty-patches / VLF propagation / multi-point observations / ionospheric exit point / vlf waves / multipoint observations / magnetosphere / geospace / ionosphere |
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| 研究開始時の研究の概要 |
Extremely Low and Very Low Frequency emissions at frequencies of 0.3-30 kHz interact with energetic electrons causing their acceleration or loss, playing an important role in radiation belt dynamics. We have little understanding on how these waves travel from the magnetosphere (alt: 1,000-60,000 km) to the ground. Using VLF ground receivers we will determine the likely position where waves exit the ionosphere. Using simultaneous detection of waves on satellites and ground we will study what affects wave propagation and discuss their effect on the loss of hazardous radiation belt electrons.
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| 研究実績の概要 |
We analyzed data from the VLF receiver at OUJ (installed in Oct. 2022) and compared to KAN, focusing on statistical results and conjugated events. VLF waves were more easily detected at KAN (occ. rate of 58%) than at OUJ (38%). Waves at L=5.5 are 20% more likely to reach the ground than at L=4.5. Occurrence rate of conjugated events was quite similar (OUJ 10% vs KAN 12%). 20-26% of waves at OUJ and KAN come from the same source region in the magnetosphere. Ionospheric exit point was on the East-West axis. Latitudinal extent of conjugated events was 1 L-shell, meaning latitudinal propagation can reflect source region size. Occurrence rate of bursty-patches were x10 lower at OUJ, even if their source region should be at those L-shells. We will continue to investigate this point further.
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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
We have analyzed OUJ data for short-term statistics and multiple conjugated events between OUJ and KAN. We have also compared with other PWING data to find general results for overall VLF wave properties. A collaboration with F. Nemec (Charles U., Czechia) used OUJ and other PWING data to asses VLF wave intensities on the ground and in space (paper under revision). The polarization code used to pinpoint ionospheric exit angles has been implemented and validated. We have also started developing a sferics filter to help with VLF bursty-patches characteristics. A paper with some of our results is currently being written. The current difficulty is processing large amounts of data, for statistics and case selection, as it has to be done by eye.
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| 今後の研究の推進方策 |
Currently, the most interesting question is that of bursty-patch propagation to the ground. To investigate this properly we will set up a PHLR and sferics filter to all PWING stations, including OUJ. We hope to have a working code by Fall 2024 and validation by the end of the year (publication expected). This will increase our chances at detecting conjugated events between KAN, OUJ, and Arase. These results will be presented at the VERSIM workshop. For selected events, we will do ray tracing analysis and triangulation of the ionospheric exit point. We hope these results will result in another paper.
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