[P-EM06_30PO1] Study of coupling processes in Sun-Earth system with large radars and large-area observations

[PEM06-P10] Naライダー/EISCATレーダー連携観測によって検出したオーロラ起因のNa層変動

*津田 卓雄¹、野澤 悟徳²、川原 琢也³、川端 哲也²、斎藤 徳人⁴、和田 智之⁴、小川 泰信¹、大山 伸一郎²、Hall Chris⁵、堤 雅基¹、江尻 省¹、鈴木 臣²、高橋 透²、中村 卓司¹ (1.国立極地研究所、2.名古屋大学太陽地球環境研究所、3.信州大学工学部、4.理化学研究所、5.トロムソ大学)

キーワード：Naライダー, EISCATレーダー, Na層, オーロラ降下粒子, 電離圏電場

Sodium atom layer is generally distributed at 80-100 km. One of mysterious subjects on high-latitude sodium layers is relationship between auroral particle precipitation and sodium atom layer variation. A previous study suggested a sodium column density decrease during a geomagnetic active period due to that the particle precipitation accompanied by electron density enhancement could induce ionization of sodium atom through their ion-molecule chemistry. Another study pointed a possibility of sodium density increase. For this reason, it is suggested that auroral precipitating particle bombardment on meteoric smoke particles can sputter sodium atoms from the smoke particles. On the other hand, ionospheric electric field, which may become more significant near auroral precipitating regions, could induce ion motions (i.e. can generate sodium ion convergence and/or divergence), and then also could affect generation and/or loss processes of sodium atoms through their ion-molecule chemistry. Thus, for the examination of the causality, it is vitally important to distinguish the effects of auroral particle precipitation and ionospheric electric field. Using a sodium lidar (which was installed in early 2010) and European incoherent scatter (EISCAT) radar at Tromsoe, Norway (69.6N, 19.2E), we have investigated, for the first time, that the actual effect of the particle precipitation to the sodium density variations without electric filed injection. In the nighttime observation on 24-25 January 2012, we detected a significant decrease of sodium atom density coincied with electron density enhancements (implying strong particle precipitations) and low ion temperatures (implying no electric field injections). These results strongly suggested that auroral particle precipitations induced sodium atom density decrease. Furthermore we discuss observed time response in the sodium density decrease.