Direct measurement of nonlinear wave-particle interaction in the magnetosphere: A simulation study of whistler-mode chorus emissions

Fukuhara et al. (Earth Planets Space, 2009) proposed the Wave Particle Interaction Analyzer (WPIA) observing interactions between plasma waves and energetic electrons directly and quantitatively in space plasmas. WPIA measurements are realized by conducting various types of calculations performed within a characteristic time scale of wave-particle interactions using wave vectors and each velocity vector of plasma particles Respectively measured by wave and particle instruments onboard a spacecraft. Specifically, an example of WPIA measurements is the inner product between the velocity of particles and the electric field of plasma waves, E dot v, corresponding to the variation of the kinetic energy of an individual particle and, equivalently, the gain of waves. WPIA has a capability of the direct measurement of the phase relation between waves and particles which is important in understanding interactions in space plasmas. To evaluate the feasibility of WPIA in analyzing wave-particle interactions and to discuss details of nonlinear wave-particle interactions, we analyze a data base of the simulation results reproducing whistler-mode chorus generation by using one-dimensional electron hybrid code. In order to simulate the WPIA measurement, we observe electromagnetic waves and the velocity vector of energetic electrons passing through the fixed observation points assumed in the simulation system, and then we conduct analyses using simulated observation results of waves and particles from the point of view of WPIA algorithms. In the result, we find significant increase of integrated values of E dot v in the wave generation region representing the wave excitation. Furthermore, we find that large integrated values are observed in the region where we observe intense wave generations. In this presentation, we also show the results of data analyses based on linear and nonlinear theories and discuss the physical meaning of E dot v in understanding nonlinear wave-particle interactions.