Japan Geoscience Union Meeting 2016

Presentation information

International Session (Oral)

Symbol P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM07] Dynamics in magnetosphere and ionosphere

Tue. May 24, 2016 1:45 PM - 3:15 PM 103 (1F)

Convener:*Yoshizumi Miyoshi(Institute for Space-Earth Environmental Research, Nagoya University), Yoshimasa Tanaka(National Institute of Polar Research), Aoi Nakamizo(Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology), Mitsunori Ozaki(Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University), Shin'ya Nakano(The Institute of Statistical Mathematics), Tomoaki Hori(Institute for Space-Earth Environmental Research, Nagoya University), Chair:Akimasa Ieda(Institute for Space-Earth Environmental Research, Nagoya University)

3:00 PM - 3:15 PM

[PEM07-06] Response of the incompressible ionosphere to the compression of the magnetosphere during the geomagnetic sudden commencements

*Takashi Kikuchi1, Kumiko Hashimoto2, Ichiro Tomizawa3, Yusuke Ebihara4, Yukitoshi Nishimura5, Tohru Araki6, Atsuki Shinbori4, B. Veenadhari7, Takashi Tanaka8, Tsutomu Nagatsuma9 (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Kibi International University, 3.Center for Space Science and Radio Engineering, University of Electro-Communications, 4.Research Institute for Sustainable Humanosphere, Kyoto University, 5.Department of Atmospheric and Oceanic Sciences, University of California, 6.Geophysical Institute, Kyoto University, 7.Indian Institute of Geomagnetism, 8.International Center for Space Weather Science and Education, Kyushu University, 9.National Institute of Information and Communications Technology)

Keywords:Incompressible ionosphere, geomagnetic sudden commencement, TM0 mode wave, ionospheric current, potential electric field

The ionospheric plasma in midlatitude moves upward/downward during the geomagnetic sudden commencement causing the HF Doppler frequency changes; SCF (+ -) and (- +) on the day- and night-sides, respectively, except for the SCF (+ -) in the evening as found by Kikuchi et al.[1985]. Although the preliminary and main frequency deviations (PFD, MFD) of the SCF have been attributed to the dusk-to-dawn and dawn-to-dusk potential electric fields, there still remain questions if the positive PFD can be caused by the compressional magnetohydrodynamic (MHD) wave and what causes the evening anomaly of the SCF. With the HF Doppler sounder, we show that the dayside ionosphere moves upward toward the sun during the main impulse (MI) of the SC, when the compressional wave is supposed to push the ionosphere downward. The motion of the ionosphere is shown to be correlated with the equatorial electrojet (EEJ), matching the potential electric field transmitted with the ionospheric currents from the polar ionosphere. We confirmed that the electric field of the compressional wave is severely suppressed by the conducting ionosphere and reproduced the SC electric fields using the global MHD simulation in which the potential solver is employed. The model calculations well reproduced the PI and MI electric fields and their evening anomaly. It is suggested that the electric potential is transmitted from the polar ionosphere to the equator by the TM0 mode waves in the Earth-ionosphere waveguide. The near-instantaneous transmission of the electric potential leads to instantaneous global response of the incompressible ionosphere.