[P-EM16] Magnetospheric Multi Scale (MMS) mission: Accomplishments and Future Plans

[PEM16-03] 磁気圏外周部におけるULF波動内で観測されたEMIC波動への水素イオンからのエネルギー輸送の直接観測

*北村 成寿¹、小路 真史²、北原 理弘³、天野 孝伸¹、大村 善治⁴、中村 紗都子²、三好 由純²、長谷川 洋⁵、加藤 雄人³、斎藤 義文⁵、寺本 万里子⁷、野村 麗子⁶、横田 勝一郎⁸、Gershman Daniel⁹、Vinas Adolfo^9,10、Giles Barbara⁹、Boardsen Scott^9,11、Pollock Craig¹²、Russell Christopher¹³、Strangeway Robert¹³、Ahmadi Narges¹⁴、Lindqvist Per-Arne¹⁵、Ergun Robert¹⁴、Burch James¹⁶ (1.東京大学大学院 理学系研究科 地球惑星科学専攻、2.名古屋大学 宇宙地球環境研究所、3.東北大学大学院 理学研究科 地球物理学専攻、4.京都大学 生存圏研究所、5.宇宙航空研究開発機構 宇宙科学研究所、6.国立天文台、7.九州工業大学、8.大阪大学大学院 理学研究科 宇宙地球科学専攻、9.NASAゴダード宇宙航空センター、10.アメリカン大学 物理学科、11.メリーランド大学、12.デナリサイエンティフィック、13.カリフォルニア大学 ロサンゼルス校 地球惑星物理学研究所、14.コロラド大学 ボルダー校 大気宇宙物理学研究所、15.スウェーデン王立工科大学、16.サウスウェスト研究所)

キーワード：MMS衛星、電磁イオンサイクロトロン波動、波動粒子相互作用

We report the temporal variation of energy transfer from hot anisotropic protons to electromagnetic ion cyclotron (EMIC) waves during a compressional ULF wave event using the data obtained by the four MMS (Magnetospheric Multiscale) spacecraft traversing the duskside outer magnetosphere. For the ULF wave, the period was about 2-5 minutes (Pc5 frequency range), and the magnetic and ion pressures were in antiphase, such that the total pressure remained almost constant. To derive the propagation velocity of the ULF wave, we applied timing method to the filtered (0.001-0.05 Hz) magnetic field data from the four spacecraft. The derived phase velocity was ~40 km/s that was comparable to E × B drift velocities. Thus, they were mirror mode type structures that have zero frequency in the plasma rest flame and we can therefore investigate the spatial size of the structure from the period and the velocity. The burst ion data from Fast Plasma Investigation Dual Ion Spectrometer (FPI-DIS) with a time resolution of 150 ms are available for two of the EMIC wave events during the ULF wave. To directly detect energy transfer from hot protons to EMIC waves, we apply the Wave-Particle Interaction Analyzer (WPIA) method to the data. The energy transfer rate by cyclotron resonance was calculated as the dot product of the wave component of the perpendicular electric fields and ion current perpendicular to the magnetic field around the resonance velocity which is called the resonant current. The energy transfer rate peaked at the local minima of magnetic field intensity, which corresponds to the maxima of the ion pressure in the compressional ULF wave. This result indicates that the spontaneous EMIC wave generation is affected by ULF waves, and preferential locations for the cyclotron resonant energy transfer are magnetic field intensity troughs with the spatial size of only ~3 times of hot proton gyro-radius. In these troughs, the relatively low resonance velocity owing to small magnetic field intensities and the enhanced hot proton flux can contribute to the enhanced energy transfer from hot protons to EMIC waves by cyclotron resonance.