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

[PEM13-12] Instantaneous Frequency Analysis on Nonlinear EMIC Emissions: Arase Observation

*Masafumi Shoji¹, Yoshizumi Miyoshi¹, Yoshiharu Omura², Lynn M Kistler^1,3, Yasumasa Kasaba⁴, Shoya Matsuda⁵, Yoshiya Kasahara⁶, Ayako Matsuoka⁵, Reiko Nomura⁷, Keigo Ishisaka⁸, Atsushi Kumamoto⁴, Fuminori Tsuchiya⁴, Satoshi Yagitani⁶, Mariko Teramoto¹, Kazushi Asamura⁵, Takeshi Takashima⁵, Iku Shinohara⁵ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.Research Institute for Sustainable Humanosphere, Kyoto University, 3.Institute for the Study of Earth Oceans and Space, University of New Hampshire, 4.Tohoku University, 5.Institute of Space and Astronautical Science, 6.Kanazawa University, 7.National Astronomical Observatory of Japan, 8.Toyama Prefecture University)

Keywords:nonlinear wave particle interaction, Arase spacecraft

In the inner magnetosphere, the Arase spacecraft has observed electromagnetic ion cyclotron (EMIC) emissions with both rising and falling frequencies. The instantaneous frequency analyses on the electromagnetic fields of the EMIC rising tone emission have been performed by the Hilbert-Huang transform. The time variation of the instantaneous frequency shows a good agreement with the nonlinear theory for the frequency evolutions. Rapid instantaneous frequency modulation is also found during the rising tone emission. We estimate the peak-to-peak time of the fluctuation in the frequency and find that the fluctuation is caused around a half of the particle trapping time. From the motion of the phase-bunched particle around the resonant velocity, it is expected that the nonlinear resonant current, which induces the falling frequency is formed in half the trapping time.