Japan Geoscience Union Meeting 2016

Presentation information

Print

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 3:30 PM - 5:00 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:Yukinaga Miyashita(Institute for Space-Earth Environmental Research, Nagoya University)

3:45 PM - 4:00 PM

[PEM07-08] Ballooning instability with the magnetosphere-ionosphere feedback coupling

*Tomo-Hiko Watanabe1 (1.Graduate School of Science, Nagoya University)

Keywords:aurora, magnetosphere-ionosphere coupling, instability

The ballooning instability has been investigated as a possible mechanism for triggering the substorm in the magnetosphere. The ballooning mode is destabilized, when the interchange term provided with the pressure gradient and the magnetic curvature overcomes the line bending term causing the shear Alfven waves. In the magnetosphere-ionosphere (M-I) coupling system in polar regions, on the other hand, the shear Alfven waves (or the kinetic Alfven waves) can also be destabilized by the magnetospheric convection, if the ionospheric density change is taken into account with the feedback mechanism [1-3].
In the present study, we have investigated the ballooning and the feedback instabilities in the same theoretical framework. Our linear analysis demonstrates that, as the interchange term increases, the "unstable" shear Alfven waves with the opposite sign of the real eigenvalues in their lowest harmonic branch collide with each other and transit to the ballooning mode. It implies that competitions and/or interactions between the two instabilities may provide a plausible explanation of auroral breakup triggered through the M-I coupling.
[1] T. Sato, J. Geophys. Res., 83, doi:10.1029/JA083iA03p01042.
[2] T.-H. Watanabe, Phys. Plasmas, 17, 022904 (2010).
[3] T.-H. Watanabe, Geophys. Res. Lett., 41, doi:10.1002/2014GL061166 (2014).