[P-EM17] 宇宙プラズマ理論・シミュレーション

[PEM17-02] Observational evidence of nonlinear growth of whistler-mode waves in an outflow of magnetopause reconnection

*北村 成寿¹、天野 孝伸²、北原 理弘³、大村 善治⁴、Boardsen Scott^5,6、三好 由純¹、中村 紗都子¹、小路 真史¹、加藤 雄人³、小嶋 浩嗣⁴、Gershman Daniel⁵、斎藤 義文⁷、平原 聖文¹、横田 勝一郎⁸、Giles Barbara⁵、Pollock Craig⁹、Le Contel Olivier¹⁰、Russell Christopher¹¹、Strangeway Robert¹¹、Lindqvist Per-Arne¹²、Ergun Robert¹³、Burch James¹⁴ (1.名古屋大学 宇宙地球環境研究所、2.東京大学大学院 理学系研究科 地球惑星科学専攻、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.NASA ゴダード宇宙飛行センター、6.メリーランド大学ボルチモア郡校 ゴダード惑星太陽圏研究所、7.宇宙航空研究開発機構 宇宙科学研究所、8.大阪大学大学院 理学研究科 宇宙地球科学専攻、9.デナリサイエンティフィック、10.プラズマ物理学研究所 フランス国立科学研究センター/エコール・ポリテクニーク/ソルボンヌ大学/パリ南大学/パリ天文台、11.カリフォルニア大学ロサンゼルス校 地球惑星宇宙科学専攻、12.スウェーデン王立工科大学、13.コロラド大学ボルダー校 大気宇宙物理学研究所、14.サウスウェスト研究所)

キーワード：ホイッスラーモード波動、磁気リコネクション、MMS衛星

In this presentation, we show observational results of nongyrotropic electrons close to the cyclotron resonance velocity, which is a key feature of nonlinear growth of whistler-mode waves, using data obtained by the Magnetospheric Multiscale (MMS) spacecraft in an outflow of asymmetric reconnection (reconnection jet) at the dayside magnetopause. Whistler-mode waves are one of the electromagnetic plasma waves, which play important roles in efficient pitch-angle scattering and acceleration of electrons in solar wind, collisionless shock waves, and planetary magnetospheres. The nonlinear wave-particle interaction theory for coherent large amplitude waves predicts that resonant electrons exhibit nongyrotropy due to phase trapping motion around resonance velocities in the presence of an appropriate inhomogeneity. The nongyrotropic electrons exchange energy and momentum with waves efficiently. Here we show examples of nongyrotropic electrons close to the cyclotron resonance velocity during whistler-mode wave events in an outflow of asymmetric reconnection (reconnection jet) at the dayside magnetopause as the observational evidence of nonlinear wave growth. Using measurements by the Fast Plasma Investigation Dual Electron Spectrometer (FPI-DES) and the search-coil magnetometer (SCM), we identified electron flux hole events that induce wave growth; a hole at an appropriate relative phase angle to the whistler-mode wave magnetic field appeared only close to the cyclotron resonance velocity at both of regions where the magnetic field direction was close to or largely different from that of the magnetosphere. The magnitudes of the gradient of the magnetic field intensity along the magnetic field line during such time intervals are consistent with an appropriate magnitude to cause phase trapping of resonant electrons. In these events, a loss cone of the magnetospheric electrons played an important role to generate temperature anisotropy around the cyclotron resonance velocity.