Excitation of magnetosonic waves in the terrestrial magnetosphere: Particle-in-cell simulations

Abstract

[1] Two-dimensional electromagnetic particle-in-cell simulations are performed to study the temporal development of an ion Bernstein instability driven by a proton velocity distribution with positive slope in the perpendicular velocity distribution f p (v ? ), where ? denotes directions perpendicular to the background magnetic field B 0 . A subtracted Maxwellian distribution is first used to construct the positive slope in f p (v ? ), and linear kinetic dispersion analysis is performed. The results of a simulation using such an initial proton distribution agree well with the linear kinetic analysis. The simulation results demonstrate that the ion Bernstein instability grows at propagation angles nearly perpendicular to B 0 and at frequencies close to the harmonics of the proton cyclotron frequency. The distribution in the simulation is further generalized to contain a proton shell with a finite thermal spread and a relatively cold ion background. The simulation results show that the presence of the cold background protons and the increase of the shell velocity shift the excited waves close to the cold plasma dispersion relation for magnetosonic waves, i.e., w r = kv A , where w r is the wave frequency, k is the wave number, and v A is the Alfvén velocity. The general features of the simulated field fluctuations resemble observations of fast magnetosonic waves near the geomagnetic equator in the terrestrial magnetosphere. A test particle computation of energetic electrons interacting with the simulated electromagnetic fluctuations suggests that this growing mode may play an important role in the acceleration of radiation belt relativistic electrons.

One-dimensional particle-in-cell simulations of electrostatic Bernstein waves in plasmas with kappa velocity distributions

“…Furthermore, the ion shell distribution was used, with finite thermal spread and a cold ion background. The results of the simulations conducted by Lui et al 22 resembled the observed fast magnetosonic waves found in different regions of the magnetosphere, consistent with their theoretical model.…”

“…Their work was motivated by observations in the terrestrial magnetosphere, near the plasma sheet boundary layer, of enhanced field fluctuation spectra, 21 believed to be produced by ion Bernstein waves. Lui et al 22 performed fully electromagnetic particlein-cell simulations to study the temporal development of an ion Bernstein instability driven by a proton velocity distribution, with a positive slope in the perpendicular velocity distribution. The subtracted Maxwellian distribution was first used to produce the positive slope, in accordance with earlier work by Gary et al, 10 to compare simulation results with those from the kinetic theory.…”

Relativistic electron scattering by large amplitude electromagnetic ion cyclotron waves: The role of phase bunching and trapping

“…The time evolution of the mean square pitch angle change, <Δ α 2 >, of the test electrons is then calculated and the time derivative of <Δ α 2 > during its linear growth phase is used to determine the pitch angle diffusion coefficient. The test particle approach studies electron scattering at a fundamental level and can well reproduce the quasi‐linear diffusion coefficients for EMIC waves [ Liu et al , 2010a, 2010b], whistler waves [ Tao et al , 2011], and fast magnetosonic waves [ Liu et al , 2011], at sufficiently small wave amplitudes. As fluctuation amplitudes increase, this approach provides clear criteria as to when quasi‐linear theory no longer provides a valid approximation for the diffusion coefficients [ Liu et al , 2010a].…”

Interactions between magnetosonic waves and radiation belt electrons: Comparisons of quasi‐linear calculations with test particle simulations

“…Both observations [Meredith et al, 2008] and simulations [Chen et al, 2010;Liu et al, 2011;Ma et al, 2014] have shown that such equatorial MS waves are preferentially excited by proton ring distributions. The signatures of MS waves include their low ellipticity, which leads to nearly linear polarization, and their nearly perpendicular propagation, which results in much stronger E ⟂ and B ∥ components compared to E ∥ and B ⟂ components, respectively .…”