[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P19] Wave normal angle of chorus waves that generate electrostatic emissions observed by the Arase satellite

*Towa Yoshida¹, Satoshi Kurita², Hirotsugu Kojima², Yoshiya Kasahara³, Shoya Matsuda⁴, Ayako Matsuoka⁵, Yoshizumi Miyoshi⁶, Tomoaki Hori⁶, Mariko Teramoto⁷, Kazuhiro Yamamoto⁶, Iku Shinohara⁸ (1.Kyoto University, 2.Research Institute for Sustainable Humanosphere, Kyoto University, 3.Emerging Media Initiative, Kanazawa University, 4.Kanazawa University, 5.Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, 6.Institute for Space-Earth Environmental Research, Nagoya University, 7.Kyushu Institute of Technology, 8.Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science)

Keywords:Chorus wave, Langmuir wave

Chorus waves are whistler mode electromagnetic waves observed in the Earth's magnetosphere, excited near the magnetic equator and propagate toward higher latitudes. Chorus waves are typically observed in the frequency range 0.1-0.8fce, where fce is the equatorial electron cyclotron frequency. Chorus waves are observed in two frequency bands with power gaps near 0.5 fce. Chorus waves are associated with various nonlinear phenomena and the important role of acceleration processes in the magnetosphere. The STEREO satellite observed an oblique whistler mode wave with distorted electric field. This distortion is from the plasma density fluctuations which driven by the electrostatic field of the whistler mode wave [Kellogg et al., 2010]. In ISEE satellite, the beam mode electrostatic bursts modulated by chorus waves have been observed [Reinleitner et al., 1982], and this modulation is caused by the Landau resonance of electrons and the chorus wave [Reinleitner et al., 1983]. Van Allen Probes observed Langmuir waves modulated by chorus waves. In addition, the electron measurements show a beam in phase space density at the Landau resonance energy of chorus waves [Li et al., 2017]. However, in these previous studies, the wave instruments covered only up to ~10kHz and did not accurately the high frequency components of electrostatic emissions. In addition, only a few cases have been analyzed by previous studies.
In order to further examine the electrostatic emissions associated with chorus waves, we perform a statistical analysis on the basis of plasma wave data obtained by the Arase satellite, which can measure waves up to 20 kHz. The oblique chorus waves play an important role in driving electrostatic emissions. However, the characteristics of wave normal angle of the chorus waves that excite electrostatic emission have not been analyzed. We performed an automatic detection of this event using data from Plasma Wave Experiment (PWI) on the Arase satellite, statistically analyzed the wave normal angle of chorus waves with electrostatic emissions. As a result, we found that chorus waves with wave normal angle ~20 degree, the occurrence of simultaneously observed electrostatic bursts was less than 5%. In contrast, oblique chorus waves with wave normal angle of about 50 degrees, the occurrence is about 15%. In addition, we analyzed the frequency where the electrostatic component of chorus waves has maximum power. When chorus waves have maximum power at 0.55fce~0.65fce, the electrostatic emissions are observed simultaneously. Furthermore, we will analyze the relation between chorus wave power and occurrences.