[P-EM28_29PM1] Magnetosphere-Ionosphere Coupling

[PEM28-10] A Simultaneous Observation of Pc 4 pulsation by Hokkaido HF Radar and Ground-Based Magnetometers

*Yuki OBANA¹, Nozomu NISHITANI², Tomoaki HORI², Mariko TERAMOTO³, Masahito NOSE⁴, Akimasa YOSHIKAWA⁵ (1.Department of Engineering Science, Osaka Electro-Communication University, 2.Solar-Terrestrial Environment Laboratory, Nagoya University, 3.Japan Aerospace Exploration Agency, 4.Graduate School of Science, Kyoto University, 5.Department of Earth and Planetary Sciences, Kyushu University)

Keywords:ULF, HF radar, M-I coupling, magnetic pulsation

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.