Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm42c0619k&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM42C-0619
Physics
2700 Magnetospheric Physics, 2720 Energetic Particles, Trapped, 2730 Magnetosphere: Inner, 7843 Numerical Simulation Studies, 7867 Wave/Particle Interactions
Scientific paper
By using a newly developed hybrid simulation scheme of electrons, pitch angle and energy diffusion processes of relativistic electrons through the wave particle interaction with electromagnetic waves are studied. To overcome the difficulty owing to the significant difference of Larmor radii between thermal electrons and relativistic electrons, we developed a new hybrid simulation scheme, where cold component of electrons are treated as a fluid and hot component of electrons are treated as particles including relativistic effects. This simulation scheme allows us to investigate the scattering process of relativistic electrons through the resonant interaction with electromagnetic waves. In the outer radiation belt, the acceleration process of relativistic electrons has been studied in details for the case of the resonant interaction with enhanced whistler mode waves (Horne and Thorne 1998; Summers et al., 1998). Although studies based on the quasi-linear approach have been achieved to explain energizing of relativistic electrons (Summers and Ma 2000; Miyoshi et al., 2003), there have been still remained problems to be evaluated. One is the nonlinear effect of plasma waves and energetic particles and the other is the accuracy of diffusion coefficients which actually control the energy range and time scale of the energization. The purpose of present study is to evaluate the diffusion coefficients derived through the previous works and the nonlinear effects possibly appeared in the energizing process of electrons by resonant interactions of energetic electrons. The comparison of the diffusion rates between the result of present numerical experiment and the quasi-linear estimation by solving the diffusion equation is performed under the same parameters of whistler mode waves and the initial distribution of high energetic electrons. The comparison is performed for the plasma parameter fp/fc is equal to 1.0. As a result, it is revealed that the quasi-linear theory tends to overestimate the energy diffusion and underestimate the rate of the pitch angle scattering taken place in the resonant interaction. This result suggests that the estimation of diffusion coefficients becomes not accurate under the low density plasma condition, owing to the assumption of wave dispersion relation in the previous studies. In addition, another possibility is pointed out that the difference is caused by a discrepancy of assumption between the simulation model and the quasi-linear theory. In the simulation model, an open system is used by treating whistler mode waves as propagating into the simulation system from external source, which seems realistic condition in the storm-time inner magnetosphere. On the other hand, in the quasi-linear theory, the diffusion in the velocity space is assumed to be under the condition that energy exchange between particles and the field is a quasi-equilibrium state in the closed system. Based on the results of present study, it is shown that the reexamination is necessary for the resonant interaction process including the treatment of appropriate plasma settings with consideration of an open plasma system as it is in the outer radiation belt during geomagnetic storms.
Iizima Masahide
Katoh Yuto
Ono Takafumi
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