HR: 1330h
AN: SM42C-0626    [PDF]
TI: Generation mechanism of chorus emissions in the dayside magnetosphere
AU: * Hikishima, M
EM: hikisima@reg.is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science and Technology, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa, 920-8667 Japan
AU: Yagitani, S
EM: yagitani@reg.is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science and Technology, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa, 920-8667 Japan
AU: Nagano, I
EM: nagano@reg.is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science and Technology, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa, 920-8667 Japan
AU: Omura, Y
EM: omura@kurasc.kyoto-u.ac.jp
AF: Radio Science Center for Space and Atmosphere, Kyoto University, Gokanosho, Uji, 611-0011 Japan
AU: Matsumoto, H
EM: matsumot@kurasc.kyoto-u.ac.jp
AF: Radio Science Center for Space and Atmosphere, Kyoto University, Gokanosho, Uji, 611-0011 Japan
AB: The chorus emissions have been observed by the GEOTAIL spacecraft around the equatorial plane in the dayside outer magnetosphere. We analyze the wave - particle interaction involved in the generation and propagation of the chorus emissions. The chorus emissions are generally considered as generated via the cyclotron resonance between electrons and whistler mode waves. Detailed examination of the measured velocity distributions of the resonant electrons has shown that their pitch angle anisotropy is too small to generate simultaneously observed chorus emissions via linear cyclotron resonance. This seems to be caused by the pitch angle scattering of cyclotron resonant electrons due to the generated chorus emissions. The whistler mode wave first grows linearly and incoherently within a certain frequency band. The unstable pitch angle anisotropy of the resonant electrons is pitch - angle scattered by the linear cyclotron interaction and rapidly reduced to the small "critical anisotropy." With such a reduced anisotropy the linear cyclotron interaction can no longer be sustained. The pitch angle scattering occurs within much less than 1 second, which is quite short enough compared with the time resolution of GEOTAIL particle measurements (several tens of seconds). This would suggest that we could observe only the "already well-reduced and marginally stable anisotropy" with GEOTAIL. In this study, by means of theoretical analysis and particle simulation, we investigate the cyclotron resonance and pitch angle diffusion of the resonant electrons, to analyze the generation mechanism of the chorus emissions.
DE: 2731 Magnetosphere--outer
DE: 2772 Plasma waves and instabilities
DE: 6984 Waves in plasma
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting