[P-EM08] Progress in Physics of the Inner Magnetosphere

[PEM08-15] プラズマ圏EMIC波動の統計解析

加藤 佑一¹、*三好 由純¹、坂口 歌織²、笠原 禎也³、松田 昇也³、桂華 邦裕¹、小路 真史¹、北村 成寿¹、長谷川 周平¹、熊本 篤志⁴、塩川 和夫¹ (1.名古屋大学太陽地球環境研究所、2.情報通信研究機構、3.金沢大学総合メディアセンター、4.東北大学大学院理学研究科　地球物理学専攻)

キーワード：電磁イオンサイクロトロン波動, 統計解析, 発生機構, 磁気音波, 空間分布

We investigate statistically the plasmaspheric EMIC wave using the Akebono/VLF measurements. The plasmaspheric EMIC waves are mainly observed at lower L-shell region (L<2). There are no significant MLT dependences and geomagnetic activities, which are different from the EMIC waves outside the plasmapause. We also investigate statistically the magnetosonic mode waves (MSW), and MSW are typically observed at L>2.5. There are some events to show that EMIC waves and MSW are simultaneous observed, suggesting that MSW convert to EMIC waves inside the plasmasphere. Considering the results from the statistical survey, we propose two different mechanisms on the origin of the plasmaspheric EMIC waves. One possibility is the cyclotron resonance with energetic ions. The estimated resonance energy of ions is a few hundred keV that are radiation belt ions. Another possibility is the mode conversion from MSW. MSW propagate radially into the inner magnetosphere after the generation at the outer portion of the plasmasphere, and then MSW convert to EMIC waves.