[P-EM13] Inner magnetosphere: Recent understanding and new insights

[PEM13-21] Magnetic field disturbances associated with the magnetic dipolarization observed by Arase (ERG) in the inner magnetosphere

*Ayako Matsuoka¹, Masahito Nose², Yoshizumi Miyoshi², Iku Shinohara¹, Mariko Teramoto², Reiko Nomura³, Akiko Fujimoto⁴, Yoshimasa Tanaka⁵, Manabu Shinohara⁶, Yoshiya Kasahara⁷, Yasumasa Kasaba⁸, Keigo Ishisaka⁹, Shoya Matsuda¹, Masafumi Shoji², Tomoko Nakagawa¹⁰, Yoichi Kazama¹¹, Shiang-Yu Wang¹¹, Satoshi Kasahara¹², Shoichiro Yokota¹³, Takefumi Mitani¹ (1.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.RISE, National Astronomical Observatory of Japan, 4.School of Computer Science and Systems Engineering, Kyushu Institute of Technology, 5.National Institute of Polar Research, 6.National Institute of Technology, Kagoshima College, 7.Information Media Center, Kanazawa University, 8.Planetary Plasma and Atmospheric Research Center, Tohoku University, 9.Faculty of Engineering, Toyama Prefectural University, 10.Faculty of Engineering, Tohoku Institute of Technology, 11.Academia Sinica Institute of Astronomy and Astrophysics, 12.School of Science, The University of Tokyo, 13.School of Science, Osaka University)

Keywords:Arase, magnetic field, dipolarization, Alfven wave

The magneto-hydrodynamic waves propagating in the plasma sheet are recognized to transport substantial energies in the magnetosphere. We investigated magnetic field disturbances of the Alfven waves observed by the Arase spacecraft at about 5 earth-radii distance in the midnight. In the inner plasma sheet Alfven waves were often accompanied by the magnetic dipolarization.
We examined the magnetic disturbances in the plane perpendicular to the ambient magnetic field. In the two events examined in our study, the magnetic field disturbances were linearly polarized and the polarization direction gradually rotated 180 degrees in 200 seconds. It is well interpreted that Arase traversed a magnetic flux tube where torsional Alfven waves propagated. The change of the polarization direction reflected the change of observation location in the flux tube. Torsional-mode is significantly common and natural as the parallel-propagating Alfven wave. It is known that large-scale energy transfer and dissipation of the torsional Alfven waves take place on the solar surface.
Meanwhile, in the boundary plasma sheet adjacent to the lobe, the magnetic field disturbances were linearly polarized again and confined to the dawn-dusk direction. They are interpreted as plane Alfven waves having uniformity in the dawn-dusk direction and propagating obliquely. The kinetic effect of the Alfven waves has been often discussed in previous works in association with the auroral emission at the ionospheric altitude.