[P-EM11] Dynamics of the Inner Magnetospheric System

[PEM11-P16] Analysis of high temporal variation in electron fluxes during the flux burst event observed by the Arase satellite

*栗田 怜¹、三好 由純²、齊藤 慎司³、加藤 雄人⁴、松田 昇也⁵、笠原 慧⁶、横田 勝一郎⁷、笠原 禎也⁵、松岡 彩子⁸、篠原 育⁹ (1.京都大学生存圏研究所、2.名古屋大学宇宙地球環境研究所、3.情報通信研究機構、4.東北大学、5.金沢大学、6.東京大学、7.大阪大学、8.京都大学理学研究科、9.ISAS/JAXA)

キーワード：あらせ衛星、コーラス、波動粒子相互作用

We examine the high temporal variation in electron fluxes during a flux burst event observed by Medium Energy Particle experiment-electron analyzer (MEP-e) onboard the Arase satellite. The flux burst event is characterized by flux increase of 17-30 keV electrons within 30 seconds at oblique (60-80 degrees) pitch angle range, which is accompanied by a decrease in electron fluxes at lower energy and pitch angle ranges [Kurita et al., 2018]. The rapid flux variation is observed in association with the appearance of intense upper-band chorus emissions. Thus it is suggested that the nonlinear wave-particle interaction between electrons and the upper-band chorus is a plausible mechanism of the flux variation. The importance of the nonlinear wave-particle interaction is examined by a test-particle simulation, and it is found that the acceleration through nonlinear phase-trapping is essential to cause the rapid flux increase [Saito et al., 2021]. It is of interest to further examine whether signatures of nonlinear electron acceleration are captured by MEP-e during the flux burst event. The flux burst event was analyzed using the MEP-e data with a time resolution of ~8 seconds (1 spin period). On the other hand, MEP-e has the capability to derive pitch angle distributions every 250ms because of its 2-pi radian disk-like field-of-view and measurement scheme. Using the pitch angle distribution with the high temporal resolution, we investigate sub-second flux variations during the flux burst event in detail. We find that the flux increase consists of two components: one is the almost same increase as the 1-spin average increase, and the other is a much larger flux increase than the 1-spin average. The larger increase is less frequently observed compared to the smaller one. Thus the larger flux increase does not significantly contribute to the 1-spin averaged flux variation. It is possible that the large flux increase seen in the 250-ms MEP-e data is a signature of electron acceleration through nonlinear wave-particle interactions. This possibility will be discussed by performing a virtual observation in a test-particle simulation domain.