Magnetosonic waves are electromagnetic emissions from a few to 100 Hz primarily confined near the magnetic equator both inside and outside the plasmasphere. Previous studies proved that MS waves can transport equatorially mirroring electrons from an equatorial pitch angle of 90$^\circ$ down to lower values by bounce resonance. But the dependence of bounce resonance effect on wave or background plasma parameters is still unclear. Here we applied a test particle simulation to investigate electron transport coefficients, including diffusion and advection coefficients in energy and pitch angle, due to bounce resonance with MS waves. We investigate five wave field parameters, including wave frequency width, wave center frequency, latitudinal distribution width, wave normal angle and root-mean-square of wave magnetic amplitude, and two background parameters, $L$-shell value and plasma density. We find different transport coefficients peaks resulted by different bounce resonance harmonics. Higher order harmonic resonances exist, but the effect of fundamental resonance is much stronger. As the wave center frequency increases, higher order harmonics start to dominate. With wave frequency width increasing, the energy range of effective bounce resonance broadens, but the effect itself weakens. The bounce resonance effect will increase when we decrease the wave normal angle, or increase the wave amplitude, latitudinal distribution width, L-shell value, and plasma density. The parametric study will advance our understanding of the favorable conditions of bounce resonance.

Lower-band chorus waves are known to play dual roles in radiation belt dynamics (electron acceleration and precipitation), and understanding their properties and excitation is very important. A systematic study of chorus waves properties in terms of background plasma parameters (electron perpendicular beta β⊥ and the ratio of plasma frequency to electron cyclotron frequency fpe /fce) has not been performed previously. We use burst mode data from Van Allen Probe A from 2014 to 2017 and develop an algorithm to extract individual lower band rising tone chorus elements. We statistically analyze four properties of rising tone chorus elements: time duration τ , frequency width ∆f , chirping rate Γ, and maximum intensity Ia. Statistical results show typical properties of chorus waves: Ia ∼ 0.09 nT, ∆f ∼0.08fce , Γ ∼2 × 103 Hz/s, τ ∼ 0.015 − 0.25 s. On the nightside and dawnside, Γ shows wider spread and is more distributed over larger values, which is associated with the wider distribution of β⊥. Chorus waves at duskside and dayside have larger values of τ , associated with smaller β⊥ and larger fpe /fce. The dependence of chorus wave properties on background plasma parameters is also examined. We show that normalized ∆f has positive correlation with β⊥ and fpe /fce. Normalized τ shows negative correlation with β⊥ and positive correlation with fpe /fce , respectively. Normalized Γ shows positive correlation with β⊥ and negative correlation with fpe /fce. These results help us better understand chorus waves excitation and their relation to the microburst.

Here we examine properties of MeV electron microbursts to better understand their generation mechanisms. Using 15 years of data from SAMPEX/HILT, >1MeV microburst repetition periods (time spacing between bursts) are examined and clear dependencies on AE, L shell, and MLT are discovered. Microburst repetition periods are shortest around 0-6 hr MLT and 4-5 Lshell, and grow longer towards the day and afternoon sectors and larger L shells. Shorter repetition periods (<1 sec) are also found to be more common during higher AE, while longer periods (>10 sec) more common during quiet times. The microburst repetition period distributions are compared directly to those of rising tone chorus wave elements and found to be similar in the night, dawn and day MLT sectors, suggesting chorus wave repetition periods are likely directly controlling those of microburst precipitation. However, dusk-side distributions differ, indicating that the dusk-side microbursts properties may be controlled by other processes.

In this study, we use observations of THEMIS and Van Allen Probes to statistically study the modulations of chorus emissions by variations of background magnetic field and plasma density in the ultra low frequency range. The modulation events are identified automatically and divided into three types according to whether the chorus intensity is correlated to the variations of magnetic field only (Type B), plasma density only (Type N) or both (Type NB). For THEMIS observations, the occurrences of the types B and N are larger than type NB, while for Van Allen Probes observations most events are Type N. The chorus intensity is mostly correlated to the magnetic field strength negatively and plasma density positively. Modulation event occurrences peak at the dawn sector. The chorus intensity tends to increase when the magnitude of the magnetic field perturbation increases, but little dependence on the amplitude of plasma density perturbation is found.

We report plasma wave observations of equatorial magnetosonic waves at integer harmonics of the local gyrofrequency of doubly-ionized helium (He++). The waves were observed by Van Allen Probe A on 08 Feb 2014 when the spacecraft was in the afternoon magnetic local time sector near L ≈ 4 inside of the plasmasphere. Analysis of the complementary in-situ energetic ion measurements (1-300 keV) reveals the presence of a helium ion ring distribution centered near 30 keV. Theoretical linear growth rate calculations suggest that the local plasma and field conditions can support the excitation of the magnetosonic waves from the unstable ring distribution. This represents the first report of the generation of magnetosonic equatorial noise via a ring distribution in energetic He++ ions in the near-Earth space plasma environment.

Recent proceedings in the radiation belt studies have proposed new requirements for numerical methods to solve the kinetic equations involved. In this article, we present a numerical solver that can solve the general form of radiation belt Fokker-Planck equation and Boltzmann equation in arbitrarily provided coordinate systems, and with user-specified boundary geometry and boundary conditions. The solver is based upon the mathematical theory of stochastic differential equations, whose computational accuracy and efficiency are greatly enhanced by specially designed adaptive algorithms and variance reduction technique. The versatility and robustness of the solver is exhibited in three example problems. The solver applies to a wide spectrum of radiation belt modeling problems, including the ones featuring nonlinear wave-particle interactions.

Russian Alpha radio navigation system (RSDN-20) emits F1=11.9kHz signals into the magnetosphere which propagate as whistler-mode waves. Observed by waveform continuous burst mode from EMFISIS on Van Allen Probes, a case is presented and featured with ducted propagation, multiple reflections and triggered emissions. Both risers and fallers appear in the triggered emissions. We use a ray-tracing method to demonstrate ducted propagation, which has a similar wave normal angle near $150^{\circ}$ as the observation. The arrival time of reflected signals is estimated using propagation analysis and compared with the observed signal arrival time. To test the non-linear cyclotron resonance theory, the order of chirping rate in triggered emission is estimated. The estimated order agrees with the observation.