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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Research Letters  

We present the first direct evidence of an in situ excitation of drift-compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift-compressional mode theory, whereas the plasma anisotropy was too small to excite the drift-mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple-nose structures of ring current protons.

DOI： 10.1029/2023GL107707

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research: Space Physics  

Internally driven Pc4-5 waves are excited in the plasmaspheric drainage plume (PDP) and near the plasmapause. The excitation of ultralow frequency (ULF) waves was investigated by using the magnetosphere-ionosphere coupled model between Geospace Environment Modeling System for Integrated Studies-Ring Current (GEMSIS-RC) and GEMSIS-POTential solver (GEMSIS-POT). In order to investigate the effects of cold plasma on the wave excitation, the simulation code to describe the dynamics of cold plasma was included in the model. The model can reproduce the shrink of the plasmasphere on the nightside and the formation of the PDP on the dayside. First, fundamental Pc5 waves are excited through the drift resonance on the dayside. The waves are caused by positive energy gradient of ion phase space density (PSD) at 50–130 keV. Second harmonic waves (drift-bounce resonance) are generated outside the plasmapause. These two types of ULF waves are also seen in the case of constant density. Unlike the case of constant density, localized eastward propagating Pc4 waves (drift resonance) are seen on the dawnside associated with the azimuthal density gradient. The azimuthal wave number of Pc4 waves is about 70 and anti-earthward gradient of PSD about 10 keV contributes to wave growth. We also detect fundamental Pc4-5 waves near the plasmapause on the nightside in the drift resonance with 100–150 keV ions. Simulation results suggest that the plasmapause has an effect to sustain the excitation of Pc4-5 ULF wave through the drift resonance.

DOI： 10.1029/2023JA031638

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開催年月日： 2024年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催年月日： 2024年5月

記述言語：英語   会議種別：口頭発表（一般）  

開催年月日： 2024年3月

記述言語：日本語   会議種別：口頭発表（一般）