2:55 PM - 3:10 PM
[PEM08-03] A method for direct measurements of wave-particle interactions in the Earth's inner magnetosphere
Keywords:whistler-mode chorus emissions, pitch angle scattering, WPIA, ERG mission, electron acceleration, wave-particle interactions
Fukuhara et al. (2009) proposed Wave-Particle Interaction Analyzer (WPIA), which is a new instrumentation measuring a relative phase angle between a wave magnetic field vector and a velocity vector of each particle and calculates the energy exchange between waves and particles. The WPIA, which enables us to directly detect wave-particle interactions in space plasmas, will be installed on the ERG satellite of JAXA/ISAS. Katoh et al. (2013) formulated measurable values of the WPIA as the Joule heat Wint and discussed the feasibility of measuring Wint. In the present study, in addition to the method to detect the energy exchange, we propose a method to directly detect the pitch angle scattering of resonant particles. The method is calculating G that is the pitch angular component of the time variation of the momentum of particles.
We apply the proposed method to results of the one-dimensional electron hybrid simulation reproducing the generation process of chorus emissions around the magnetic equator [Katoh and Omura, 2007]. In the result of the analysis, we obtain significant values of G for electrons in the kinetic energy and pitch angle ranges satisfying the cyclotron resonance condition with the reproduced chorus emissions. We compared the result of the analysis of G with the temporal variation of both the pitch angle distributions and the wave spectra observed at fixed points in the simulation. While the velocity distribution function varies similarly in both hemispheres, the obtained time variation of the momentum is only significant in the pitch angle range corresponding to electrons moving northward (southward) in the southern (northern) hemisphere, indicating the pitch angle scattering of electrons by chorus emissions propagating away from the equator. The results of the present study demonstrate that the proposed method enables us to identify the location where wave-particle interactions occur in the simulation system. Furthermore, we re-examine the formula of the measurement values Wint to detect the energy exchange, based on the discussion of the quantity G.