HR: 1340h
AN: SM23A-0489    [Abstracts]
TI: Cyclotron interaction for the chorus emissions in a nonuniform magnetic field
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@rish.kyoto-u.ac.jp
AF: Research Institute for Sustainable Humanosphere, Kyoto University, Gokanosho, Uji, 611-0011 Japan
AU: Matsumoto, H
EM: matsumot@rish.kyoto-u.ac.jp
AF: Research Institute for Sustainable Humanosphere, Kyoto University, Gokanosho, Uji, 611-0011 Japan
AB: The chorus emissions have been frequently observed by the GEOTAIL spacecraft around the equatorial plane in the dayside outer magnetosphere. The chorus emissions consist of the elements with rapid frequency variation in a few seconds, and it is generally considered that they are generated via nonlinear wave-particle interaction between anisotropic electrons and whistler mode waves. The exact mechanisms of the chorus emissions involved in complicated behavior in amplification and nonlinear frequency shift of chorus emissions are not yet well clarified. We have confirmed an evidence of wave-particle interaction of the chorus emissions from comparison between wave and particle data simultaneously observed onboard GEOTAIL. It is found that the resonant electrons are pitch-angle diffused through the linear cyclotron interaction so that the initially unstable pitch-angle anisotropy is rapidly reduced to the small "critical anisotropy." We also analyze the cyclotron growth and propagation mechanisms of the whistler mode waves by using electromagnetic particle simulation. As the simulation model, we inject the whistler mode wave parallel to the magnetic field into hot electrons with large anisotropy in a one-dimensional model. From the simulation result, the resonant electrons with the resonant velocity corresponding to the wave frequency are pitch-angle diffused, then the initially unstable anisotropy decreases down to the stable anisotropy, which is onsistent with the GEOTAIL observation. We will show and discuss the evolution of the resonant electrons and the frequency shift of the chorus emissions in a nonuniform magnetic field.
DE: 7843 Numerical simulation studies
DE: 7867 Wave/particle interactions
DE: 2731 Magnetosphere--outer
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting