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Both proton ring and shell distributions, providing a positive gradient along the perpendicular direction, can trigger ion Bernstein instabilities and excite magnetosonic (MS) waves in the Earth’s inner magnetosphere. A thorough comparison of the ion Bernstein instability due to the proton ring and shell distributions has not been performed. In this study, we perform and compare the MS wave instabilities under different wave normal angles and parameters of ring and shell distributions. We find that (1) compared to shell-driven MS waves, ring-driven MS waves have narrower frequency and wavenumber ranges. (2) The peak growth rates of shell-driven MS waves are always near the first peaks of the square of first-kind Bessel function Jn2. While, The peak growth rates of ring-driven MS waves are near the first peaks of Jn2, and shift to the cold plasma dispersion relation as ring velocity or wave normal angle increases. (3) MS wave growth rates increase as first peaks of Jn2 approach the cold plasma dispersion in frequency-wavenumber domain. This result can be used to explain dependences on ring (shell) velocity and wave normal angle. (4) The MS wave frequency range and growth rates decrease with increasing ring or shell temperature.

Abstract Chorus waves are intense electromagnetic emissions critical in modulating electron dynamics. In this study, we perform two‐dimensional particle‐in‐cell simulations to investigate self‐consistent wave‐particle interactions with oblique chorus waves. We first analyze the electron dynamics sampled from cyclotron and Landau resonances with waves, and then quantify the advection and diffusion coefficients through statistical studies. It is found that phase‐trapped cyclotron resonant electrons satisfy the second‐order resonance condition and gain energy from waves. While phase‐bunched cyclotron resonant electrons cannot remain in resonance for long periods. They transfer energy to waves and are scattered to smaller pitch angles. Landau resonant electrons are primarily energized by waves. For both types of resonances, advection coefficients are greater than diffusion coefficients when the wave amplitude is large. Our study highlights the important role of advection in electron dynamics modulation resulting from nonlinear wave‐particle interactions.

Abstract Chorus subpackets are the wave packets with modulated amplitudes in chorus waves, commonly observed in the magnetospheres of Earth and other planets. Nonlinear wave‐particle interactions have been suggested to play an important role in subpacket formation, yet the corresponding electron dynamics remain not fully understood. In this study, we have investigated the electron trapping through cyclotron resonance with subpackets, using a self‐consistent general curvilinear plasma simulation code simulation model in dipole fields. The electron trapping period has been quantified separately through electron dynamic analysis and theoretical derivation. Both methods indicate that the electron trapping period is shorter than the subpacket period/duration. We have further established the relation between electron trapping period and subpacket period through statistical analysis using simulation and observational data. Our study demonstrates that the nonlinear electron trapping through cyclotron resonance is the dominant mechanism responsible for subpacket formation.

Abstract A 2‐D GCPIC simulation in a dipole field system has been conducted to explore the excitation of oblique whistler mode chorus waves driven by energetic electrons with temperature anisotropy. The rising tone chorus waves are initially generated near the magnetic equator, consisting of a series of subpackets, and become oblique during their propagation. It is found that electron holes in the wave phase space, which are formed due to the nonlinear cyclotron resonance, oscillate in size with time during subpacket formation. The associated inhomogeneity factor varies accordingly, giving rise to various frequency chirping in different phases of subpackets. Distinct nongyrotropic electron distributions are detected in both wave gyrophase and stationary gyrophase. Landau resonance is found to coexist with cyclotron resonance. This study provides multidimensional electron distributions involved in subpacket formation, enabling us to comprehensively understand the nonlinear physics in chorus wave evolution.

Abstract 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.

Abstract Here we examine properties of MeV electron microbursts to better understand their generation mechanisms. Using 15 years of data from Solar, Anomalous, Magnetospheric Particles Explorer/Heavy Ion Large Telescope, >1 MeV microburst repetition periods (time spacing between bursts) are examined and clear dependencies on Auroral Electrojet (AE), L shell, and magnetic local time (MLT) are discovered. Microburst repetition periods are shortest around 0–6 hr MLT and 4–5 L shell, and grow longer toward the day and afternoon sectors and larger L shells. Shorter repetition periods (10 s) 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.

Abstract The frequency chirping of chorus waves is commonly observed in the Earth’s inner magnetosphere, but its generation remains an open question. Recently, Liu et al. (2021), https://doi.org/10.1029/2021JA029258 reported two unusual rising‐tone (upward chirping) chorus elements. Although the central frequency of constituent subpackets rises, the frequency of a single subpacket is surprisingly downward chirping. With a gcPIC‐δf simulation in the dipole field, we successfully reproduce this kind of substructure, which contains alternating signs of chirping. Interestingly, both hole and hill structures are formed around the theoretical resonant velocities in the electron phase space, no matter whether the chirping is upward or downward. However, during each chirping interval, only one structure (either a hole or a hill) is associated with wave excitation: the upward chirping is related to the hole, while the hill contributes to the downward chirping. Our study provides a fresh perspective on the theory of frequency chirping in chorus waves.

In this study, we use approximately 3 years of observations from the Exploration of energization and Radiation in Geospace (ERG/Arase) satellite to statistically study the meridional distribution of wave power from very-low-frequency (VLF) ground transmitters in the inner magnetosphere and analyze the corresponding latitudinal dependence. The results show that the mean intensity of NWC transmitter signals decreases as the transmitter emission propagates from the southern latitude (∼—30°) region to the equator in the inner magnetosphere and then increases as the emission propagates to the northern latitude (∼30°) region again. Similar latitudinal dependence can be found from the Van Allen Probes’ observation with a narrower latitude range (∼−20° to 0°). A ray-tracing simulation of the transmitter emission propagation is performed and reproduces a meridional wave power distribution similar to the observation. Similar latitudinal dependence can also be found for NAA, NLK and NLM transmitters.

Microbursts are impulsive (

Microbursts, short-lived but intense electron precipitation observed by low-Earth-orbiting satellites, may contribute significantly to the losses of energetic electrons in the outer radiation belt. Their origin is likely due to whistler mode chorus waves, as evidenced by a strong overlap in spatial correlation of the two. Despite previous efforts on modeling bursty electron precipitation induced by chorus waves, most, if not all, rely on the assumption that chorus waves are ducted along the field line with zero wave normal angle. Such ducting is limited to cases when fine-scale plasma density irregularities are present. In contrast, chorus waves propagate in a nonducted way in plasmas with smoothly varying density, allowing wave normals to gradually refract away from the magnetic field line. In this study, the interaction of ducted and nonducted chorus waves with energetic electrons is investigated using test particle simulation. Substantial differences in electron transport are found between the two different scenarios, and resultant electron precipitation patterns are compared. Such a comparison is valuable for interpreting low Earth-orbiting satellite observations of electron flux variation in response to the interaction with magnetospheric chorus waves.

Observations from Van Allen Probes are analyzed to obtain the statistical wave normal distribution of lightning-generated whistlers (LGWs). An automatic algorithm is developed to identify burst mode waveform data with LGW signals and analyze the wave polarization information for these LGW signals. The spatial distribution of the LGW occurrence and the probabilities of different propagation types demonstrate that most LGWs can be observed in the low L-shell region (L < 3), where the dominant propagation type is oblique outward. Parallel propagation dominates in the high L-shell region, but the LGW occurrence is very small. Additionally, a small group of oblique but inwardly propagating LGWs are observed at low altitudes (<0.2RE). A ray tracing simulation is performed not only to confirm predominant oblique and outward wave vectors in the vast region of the plasmasphere but also to verify the existence of these inward propagating LGW signals at low altitudes near the topside ionosphere. [ABSTRACT FROM AUTHOR]

Magnetosonic (MS) 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° down to lower values by bounce resonance. However, the dependence of the 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 root-mean-square of wave magnetic amplitude, and two background parameters, L-shell value and plasma density. We find different transport coefficient peaks resulting from 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. [ABSTRACT FROM AUTHOR]

This article is an editorial that discusses the circulation of heavy ions and their role in regulating the dynamics of near-Earth plasma. The research in this field has gained attention in recent years, with studies focusing on the composition of ions, their sources and sinks, and how they affect magnetospheric processes. The editorial synthesizes insights from five recent papers, which cover topics such as ion upflow during aurora events, atmospheric loss cone for energetic particles, magnetospheric mass density, nitrogen ion observations, and the dynamics of ion fluxes in turbulent magnetotail dipolarizations. These studies highlight the complexity and significance of heavy ions in understanding Earth's space environment and have implications in solar, ionospheric, and magnetospheric physics. [Extracted from the article]