PPARCセミナー (2025/11/7)
PPARCセミナー (2025/11/7)
(1)
[Name]
Riku Kikuchi
[Title]
地球磁気圏のEMIC波：Arase衛星による偏波解析とイオン組成導出の試み
EMIC Waves in the Magnetosphere: Attempts to Derive Ion Composition Using Polarization Analysis by the Arase Satellite
[Abstract]
Electromagnetic ion cyclotron (EMIC) 波は、温度異方性のあるイオンにより励起される低周波電磁波動であり、その観測から周辺プラズマのイオン組成を推定することが潜在的に可能である。粒子計測器では10-20 eVを下回る低エネルギーイオンの定常的な観測が困難であるが、EMIC波を用いればそのような粒子のイオン組成を導出することができる。これまでにAkebono衛星やVan Allen Probes (RBSP) 衛星により、イオン組成の推定に有益なEMIC波モード変換イベントが報告されている。一方、Arase衛星におけるモード変換の観測事例は限定的で、イオン組成に関する詳細な議論は行われていない。本研究は、Arase衛星の3軸磁場波形データを用いてEMIC波のより広範な観測事例を調べ、電離圏のトップサイドからプラズマ圏における低温イオンの組成分布とその変動を見出すことを目的として着手された。本解析は、「S/Nの良く、H+、He+、O+のサイクロトロン周波数を跨ぐ広帯域のEMIC波」を探索するべく、PWE WFC (Wave Form Capture) 1,024 Hz波形データ(EMIC-Burst: 間欠的データ)、および MGF (Magnetic Field Experiment)による背景磁場情報を用いる。本発表では、2017年3月から2024年8月までの期間におけるWFCデータに対するイベントサーチ結果, 及び偏波解析結果によるイオン組成導出結果を示す.
Electromagnetic ion cyclotron (EMIC) waves are low-frequency, circularly polarized electromagnetic waves excited by anisotropic ion distributions and their observation can be a tool for estimating the ion compositions of the surrounding plasma. While particle instruments onboard satellites often struggle to detect low-energy ions below 10-20 eV, EMIC wave analysis can provide insight into the composition of these cold ions. Previous observations by the Akebono satellite and Radiation Belt Storm Probes (RBSP) have reported on mode conversion events, which are useful for ion composition estimation.However, only one mode conversion event has been reported by the Arase satellite, and ion compositions have not been extensively discussed. This study aims to investigate EMIC waves more comprehensively using magnetic field data from the Arase satellite to determine the distribution and dynamics of cold ion compositions from the topside ionosphere to the plasmasphere. The analysis utilizes 1,024 Hz waveform data from Wave Form Capture (WFC) (EMIC-Burst data: intermittent data) on PWE, and also ambient magnetic field data from Magnetic Field Experiment (MGF) onboard the Arase satellite. The search specifically targets “EMIC waves with sufficient S/N ratios and broad frequency coverage across the cyclotron frequencies of H+, He+ and O+.” In this seminar, I will show the event search results using WFC data from March 2017 to August 2024, as well as the derived ion composition results based on polarization analysis.
(2)
[Name]
Yasumasa Kasaba
[Title]
Plasma and radio waves in BepiColombo [and JUICE]: Progress and Plans
[Abstract]
Beyond Arase Plasma Wave Experiment (PWE), we are running two major
collaborations with Europe. The first is Plasma Wave Investigation
(PWI) aboard the Mio spacecraft of BepiColombo, ESA-JAXA joint mission
to Mercury, which will observe Mercury on the orbit from the end of 2026.
The second is Radio and Plasma Wave Investigations (RPWI) aboard ESA
JUpiter ICy moons Explorer (JUICE) to Jupiter, which will observe Jovian
system on the orbit from 2031.
In both Japan and Europe, main players are overlapped and collaborating
strongly in both and beyond.
We show followings:
(1) BepiColombo/Mio PWI
Results and publications from all Mercury flybys #1-#6
Initial Plan after the Mercury Orbit Insertion in the end of 2026
[based on BepiColombo Science Working Group meetings
@ Roma (July 2025) + ESA/ESAC (Oct 2025)]
[(2) JUICE RPWI
From Lunar-Earth flyby (Aug 2024) toward next Earth flyby (Sep 2026),
and beyond
[based on Kasaba+ SGEPSS 2025 Fall meeting]
