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Chorus subpackets/subelements are the wave packets occurring at intervals of ∼10–100 msec and are suggested to play a crucial role in the formation of substructures within pulsating aurora. In this study, we investigate the evolution of subpackets from the upstream to downstream regions. Using Van Allen Probe A measurements, we have found that the frequency of the upstream subpackets increases smoothly, but that of the downstream subpackets remains almost unchanged. Through a simulation in the real‐size magnetosphere, we have reproduced the subpackets with characteristics similar to those in observations, and revealed that the frequency chirping is influenced by both resonant current of electrons and wave amplitude due to nonlinear physics. Although the resonant currents in the upstream and downstream regions are comparable, the wave amplitude increases significantly during evolution, resulting in lower sweep rate in the downstream region. Our findings provide a fresh insight into the evolution of chorus subpackets.

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 correlates to the variations of the magnetic field only (Type B), plasma density only (Type N), or both (Type NB). For the THEMIS observations, the occurrences of the Types B and N are larger than Type NB, while for the Van Allen Probes observations, most events are of Type N. The chorus intensity is mostly correlated to the magnetic field strength negatively and plasma density positively. The chorus intensity tends to increase when the magnitude of the magnetic field perturbation increases, but little dependence on plasma density perturbation amplitude is found.

The lower hybrid (LH) waves are electrostatic emissions near the LH resonant frequency. They propagate perpendicularly with a small wavelength comparable to Larmor radius of thermal particles and can be capable of heating both ions and electrons. In this study, we statistically study the global distribution of LH waves in the inner magnetosphere by using Van Allen Probes observation from 2012 to 2018. We find that (a) LH waves are commonly observed in the inner magnetosphere. Most LH waves are confined near the magnetic equator with typical amplitudes of 0.02–0.2 mV/m and occurrence rates up to 10%. (b) LH waves extend to innerLregions with increasing wave amplitudes as AE* increases. (c) Weak LH waves occur at the nightside inside the plasmapause. Moderate and strong LH waves occur at the nightside and noon inside the plasmapause. As AE* increases, they extend to all magnetic local times inside the plasmapause and dawnside outside the plasmapause.

In this study, we statistically investigate the features of magnetic dips by constructing superposed epoch analysis on Van Allen Probe data. Based on the values of electron and proton plasma betas, we categorize dips into two types: electron‐dominant and proton‐dominant. The global distributions of dips are obtained. Superposed epoch analysis on two types reveals a correlation between the magnetic fluctuations and plasma betas. Moreover, the occurrences of butterfly pitch angle distributions of relativistic electrons driven by the magnetic dips are confirmed on a statistical basis. Our results reveal the statistical characteristics of magnetic dips and establish the relationship among the magnetic fluctuations and background plasma parameters, indicating the potentially important role of magnetic dips in the inner magnetosphere dynamics.

Radiation belt electrons can be accelerated and scattered by magnetosonic waves in the Earth's magnetosphere, and the scattering rate of electrons is sensitive to the wave normal angle. However, observationally it is difficult to identify the wave normal angle within a few degrees. In this study, using 2‐D particle‐in‐cell (PIC) simulations, we investigate the wave normal angle distribution of magnetosonic waves excited by ring distribution protons. Both the linear theory and simulations have shown that the wave normal angles are distributed over a narrow range (82°–89°) with a major peak at about 85° during the linear growth stage when the proton ring velocity is close to the Alfven speed. In addition, 2‐D PIC simulations further demonstrated that the waves tend to have larger wave normal angles (84°–89°) during the saturation stage since the waves with smaller wave normal angles are dissipated faster. It is also found that wave normal angles decrease with the increase of wave frequency. With the increase of the ring velocity of the proton ring distribution, the perpendicular wavenumber of excited magnetosonic waves decreases, which leads to the decrease of the wave normal angle. The simulation results provide a valuable insight to understand the property of magnetosonic waves, and the findings are useful for the global simulations of radiation belt dynamics.

In this study, we use about 6.5 years of observation of Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite to study the spectral broadening of NWC ground transmitter signals and examine key parameters that control the width and intensity of the broadening power. First, we analyze a typical spectral broadening event, with enhanced wave intensity between lower hybrid resonance frequency and NWC signal frequency (19.8 kHz). The width and intensity of broadening power are positively proportional to the NWC wave amplitude. A following statistical analysis reveals a similar dependence on the NWC wave amplitude. The statistical analysis also indicates a significantly negative correlation of broadening spectral intensity and width with the background plasma density. The observations are consistent with existing theories predicting that lower plasma density drives a lower threshold for spectral broadening.