[P-EM28_29PM1] 磁気圏-電離圏結合

[PEM28-10] 北海道HFレーダーと地上磁場におけるPc 4脈動の同時観測研究

*尾花 由紀¹、西谷 望²、堀 智昭²、寺本 万里子³、能勢 正仁⁴、吉川 顕正⁵ (1.大阪電気通信大学工学部基礎理工学科、2.名古屋大学太陽地球環境研究所、3.宇宙航空研究開発機構 宇宙科学研究所、4.京都大学大学院理学研究科、5.九州大学大学院理学研究院地球惑星科学部門)

キーワード：ULF, HFレーダー, 磁気圏電離圏結合, 地磁気脈動

We studied a Pc 4 (6.7-22.2 mHz) oscillation of ionospheric Doppler plasma velocity observed around the dawn terminator on 16 Jul 2013 on an east-northeast pointing beam 14 of SuperDARN Hokkaido HF radar in Japan. We compared this ionospheric Pc 4 oscillation with magnetic field variation at St. Paratunka (PTK) in Russia, Kakioka (KAK) in Japan, Guam (GUA), Middlemarch (MDM) and Te Wharau (TEW) in New Zealand. PTK and conjugate points of MDM and TEW are located almost under the radar beam. The waveforms showed high similarity among the HF Doppler, the D (east-west) component of magnetic field at stations in the middle latitude of northern hemisphere (PTK and KAK). While, at the other stations (MDM, TEW, and GUA) the H (north-south) component of magnetic field showed high similarity to the HF Doppler. Using the value of the peak-to-peak amplitude of the HF Doppler velocity, we estimated amplitude of magnetic field variation with assuming a horizontal current sheet infinitely extended in the ionosphere. The estimated amplitude was comparable to the observed amplitude at PTK. We also studied longitudinal variation in amplitude using magnetic field data at Amsterdam Isl. (AMS) in South Indian Ocean and Fredericksburg (FRD) in the United States. The maximum amplitude was found at AMS which located around the midnight. These results can be interpreted as follows. This event had its source from night side and the Doppler velocity oscillation was caused by an oscillating electric field in the east-west direction. In the northern hemisphere (PTK and KAK), the ionosphere above the observatory was sunlit, thus the ionospheric Hall current induced by the electric field makes D component of magnetic filed oscillation on the ground. On the other hand, in the southern hemisphere (MDM and TEW) and GUA, the ionosphere above the stations was still in the darkness, thus effective ionospheric current could not be induced due to low conductivity. The H component of magnetic field oscillation may reflect direct incidence of magnetic field oscillation from the magnetosphere to the ground.