日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 P (宇宙惑星科学) » P-EM 太陽地球系科学・宇宙電磁気学・宇宙環境

[P-EM13] 内部磁気圏

2019年5月29日(水) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:海老原 祐輔(京都大学生存圏研究所)、Danny Summers(Memorial University of Newfoundland)、三好 由純(名古屋大学宇宙地球環境研究所)、齊藤 慎司(名古屋大学 大学院理学研究科)

[PEM13-P04] Sudden enhancements of electron cyclotron harmonic waves observed by the Arase satellite

*新城 藍里1小嶋 浩嗣1笠原 禎也2風間 洋一3臼井 英之4三好 由純5笠羽 康正6松田 昇也7堀 智昭5S. Wang8Sunny Tam9熊本 篤志10松岡 彩子11 (1.京都大学生存圏研究所、2.金沢大学総合メディア基盤センター 、3.ASIAA、4.神戸大学 大学院 システム情報学研究科 、5.名古屋大学宇宙地球環境研究所 、6.東北大学 惑星プラズマ・大気研究センター 、7.宇宙航空研究開発機構 宇宙科学研究所 、8.台湾・中央研究院、9.台湾・成大・宇宙プラズマ、10.東北大学大学院理学研究科地球物理学専攻 、11.宇宙航空研究開発機構 宇宙科学研究所 太陽系科学研究系 )

Electron cyclotron harmonic (ECH) waves are commonly observed in the low latitude region just outside the terrestrial plasmapause. They are purely electrostatic and their frequency spectra show harmonic structures. The harmonic structures are believed to depend on the temperature and density ratio between cold and hot background electrons. The Plasma Wave Experiment (PWE) onboard the Arase satellite has observed ECH waves since the start of its operation. The observed ECH waves are classified into two types. They are the diffuse ECH waves and the enhanced ECH waves. The diffuse ECH waves are weak and they appear as continuous emissions that last for more than a few minutes. The enhanced ECH waves are the sudden enhancements of the diffuse ECH in shorter periods. The present paper focuses on the enhanced ECH waves observed by the Arase satellite.

Kazama et al. (2018) introduced the event that the repeated enhancement of ECH waves is associated with density depletions near the plasmapause. They succeeded in revealing the good correlation of the enhancement of the ECH waves and the sudden decrease of the cold electrons with energies lower than the lowest energy limit of the particle detector. The observed electron features are clear in the relation to the enhancement of ECH waves, but the mechanism of the enhancement is still unclear. We searched for such events of the enhanced ECH waves and examined the correlation of wave intensities, spacecraft potentials and electron velocity distributions observed by the Arase satellite. Some of the events show the features similar to those of Kazama et al. (2018), but there are also many other events with no correlation between the enhancements of the ECH waves and the density depletions. In the present paper, we examine velocity distribution functions of electrons observed by the low-energy particle experiments-electron analyzer (LEPe) onboard Arase. Velocity distribution functions allow us to examine temperature anisotropies of electrons and calculate linear dispersion relations for the ECH waves. Once we get electron temperatures, resonance velocities are calculated. On the other hand, since the wavelength of the ECH waves is very short, the relation of the wavelength and the length of the Arase electric field sensors is also important in evaluating the time variations of the ECH wave intensity. We study the enhanced ECH waves in various viewpoints using wave and electron data observed by the Arase satellite and discuss the generation mechanism in the present paper.