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.

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.

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.