[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P08] Local time dependence of energetic electron precipitation induced by the VLF signal from the ground-based transmitter

*栗田 怜¹、野田 周英¹、笠原 禎也²、松田 昇也²、土屋 史紀³、熊本 篤志³、堀 智昭⁴、新堀 淳樹⁴、三好 由純⁴、篠原 育⁵ (1.京都大学生存圏研究所、2.金沢大学、3.東北大学、4.名古屋大学宇宙気球環境研究所、5.宇宙科学研究所)

キーワード：VLFトランスミッター、波動粒子相互作用、電子降り込み、あらせ衛星

Intense signal from ground-based VLF wave transmitters can go through the ionosphere and penetrate into the magnetosphere, where they propagate further as whistler mode waves. The waves can resonantly interact with energetic electrons in the inner magnetosphere, resulting in the precipitation loss of electrons in the radiation belts. Previous studies show that a day-night asymmetry in the signal intensity of the VLF transmitters in the magnetosphere. Such an asymmetry of the signal intensity is attributed to the day-night variation in the ionospheric density, which is caused by presence and absence of the enhanced ionization of high-altitude atmosphere controlled by the solar illumination. Since the ionospheric density strongly depends on the local time, it is expected that the intensity of the VLF transmitter signals observed in the magnetosphere also depends on the local time and hence the resultant energetic electron precipitation may also have similar dependence. In this study, we analyzed the data obtained by the Arase satellite and the POES satellites to investigate local time dependence of the VLF transmitter signals in the magnetosphere and energetic electron precipitation. We find that the electron precipitation shows expected dependence on local time, and discuss the cause of the dependence from the point of view of resonance energy. It is revealed that local time dependence of the resonance energy can be a candidate to cause the local time dependent precipitation of energetic electrons due to the VLF transmitter signals.