Instantaneous Frequency Analysis on Nonlinear EMIC Emissions: Arase Observation

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 transfor...

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Bibliographic Details
Published in:Geophysical research letters 2018-12, Vol.45 (24), p.13,199-13,205
Main Authors: Shoji, Masafumi, Miyoshi, Yoshizumi, Omura, Yoshiharu, Kistler, Lynn M., Kasaba, Yasumasa, Matsuda, Shoya, Kasahara, Yoshiya, Matsuoka, Ayako, Nomura, Reiko, Ishisaka, Keigo, Kumamoto, Atsushi, Tsuchiya, Fuminori, Yagitani, Satoshi, Teramoto, Mariko, Asamura, Kazushi, Takashima, Takeshi, Shinohara, Iku
Format: Article
Language:English
Subjects:
Arase
Cyclotrons
Electromagnetic fields
EMIC wave
Emission analysis
Emissions
ERG
Falling
Frequency analysis
Frequency dependence
Frequency modulation
Genetic transformation
instantaneous frequency
Magnetosphere
Magnetospheres
Nonlinear analysis
nonlinear wave particle interaction
rising tone
Spacecraft
Trapping
Variation
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Summary: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. Plain Language Summary The Arase spacecraft observed nonlinear EMIC rising and falling tone emissions in the inner magnetosphere. Instantaneous frequency of nonlinear EMIC rising tone emission is analyzed by Hilbert‐Huang Transformation. Fast frequency modulation of the rising tone emission is found in the instantaneous frequency, which can be caused by the phase‐bunched particles in the phase space. Key Points Typical nonlinear EMIC rising and falling tone emissions have been observed by the electric and magnetic field detectors onboard Arase Instantaneous frequency of a rising tone emission is analyzed and compared with the nonlinear growth theory EMIC waves have short‐time frequency modulations caused by phase‐bunched ion motion in the phase space
ISSN:0094-8276
1944-8007
DOI:10.1029/2018GL079765