Xueyi Wang

Mars possesses a unique plasma environment formed by the interaction between the solar wind and the Martian induced magnetosphere. Ion escape from Mars has long been recognized as a key process governing the evolution of the Martian atmosphere and climate. Global hybrid simulations provide a powerful tool for investigating the large‐scale Martian plasma environment while retaining ion kinetic effects. However, many recent hybrid models simplify ionospheric ion production by prescribing ion emission from the ionosphere. In this study, we have developed a new three‐dimensional (3‐D) global hybrid simulation model, the general curvilinear plasma simulation code for Mars (GCPIC‐M), in which ionospheric ion production is self‐consistently determined through photochemical reactions. Under given upstream solar wind conditions, the simulated heavy ion density profiles in the ionosphere agree well with Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Using this model, we have quantified planetary ion escape and investigated its dependence on the interplanetary magnetic field (IMF) cone angle. The simulated escape rates are on the order of s ⁻¹ , consistent with typical values in observations. Moreover, the escape rate exhibits a nonmonotonic dependence on IMF cone angle, reaching a maximum of ∼7 × s ⁻¹ near ∼, where foreshock wave activity is enhanced. These results highlight the kinetic nature of Martian ion escape and the importance of IMF geometry. By self‐consistently linking ion production, transport, and atmospheric escape, GCPIC‐M provides a unified framework for investigating ion kinetic processes in the Martian plasma environment.

Magnetic reconnection at the dayside magnetopause is the primary pathway for transferring mass, momentum, and energy from the solar wind into the terrestrial magnetosphere. Previous studies have shown that the spatiotemporal dynamics of dayside magnetic reconnection can be inferred remotely from properties of Earth's cusps, specifically their ion dispersion signatures, as well as structure and location within the magnetosphere. Despite the abundance of in situ cusp observations from multiple space‐based instruments, intermittent sampling spacecraft moving quickly along their trajectories precludes characterization of the cusp's global response to dynamic upstream drivers. To overcome this limitation, we leveraged existing data sets to develop a machine learning‐based model of three‐dimensional ion fluxes in the high‐altitude northern cusp that are modulated by solar‐wind forcing. This model is based on a residual neural network trained on solar wind parameters from NASA's OMNIWeb database, and ion flux measurements from the CIS/HIA instrument aboard ESA's Cluster mission. The model reproduces longitudinal and latitudinal displacements of the cusp under ‐ and ‐dominated interplanetary magnetic field regimes, in close agreement with reconnection theory. To quantify uncertainty and evaluate performance, we use an ensemble of 100 identical networks with randomized training and validation splits, reserving a fixed test set shared by all models. The statistics indicate consistent predictions within the central cusp region. Also, we used Shapley Additive exPlanations to visualize input feature contributions to the model's outputs. The analysis suggests that the magnitude of ion fluxes within the cusp is most strongly associated with , and solar wind parameters.

Chorus waves are coherent whistler‐mode emissions in Earth’s magnetosphere and play a key role in the acceleration and loss of radiation belt electrons. Their spectra commonly consist of discrete and repetitive elements, yet the mechanism governing this repetition is not fully understood. Using typical magnetospheric plasma parameters, we perform simulations to investigate the excitation of repetitive chorus elements. The repetition period is quantified and its dependence on plasma parameters and the background magnetic‐field configuration is examined. The results identify two factors controlling chorus element repetition: external energetic‐electron injection and intrinsic nonlinear wave growth. Energetic‐electron injection replenishes free energy, whereas nonlinear growth converts this free energy into wave energy. Specifically, the repetition period increases with the electron injection timescale but decreases with the nonlinear growth rate. Standardized regression coefficients indicate a slightly stronger influence of nonlinear wave growth on the repetition period.

Electromagnetic ion cyclotron (EMIC) waves contribute to magnetospheric loss cone scattering, but the fundamental processes during EMIC wave formation and evolution have not been systematically studied. We examine the formation of EMIC waves, driven by temperature anisotropy, in a uniform plasma using one‐dimensional (1D) and two‐dimensional (2D) hybrid simulations in proton‐only and hydrogen‐helium mixed plasmas. In a 1D plasma, a hot proton population with sufficient temperature anisotropy leads to the growth of parallel‐propagating EMIC waves in line with the predictions of the linear‐fit dispersion relation. The changing plasma temperatures and wave structures during EMIC wave evolution are illustrated. Additionally, a standing structure with parallel wave‐vector was found to act as a mechanism for parallel heating of the cold background plasma. This electrostatic structure emerges with half the EMIC wavelength, and is generated by nonlinear EMIC self‐interaction. In the 2D case, we observe the formation of structures possessing perpendicular wavenumbers and a broad‐spectrum overlap between the EMIC and electrostatic waves leading to locally enhanced amplitudes. In simulations with a cold helium population, we note specific contributions of each ion species to the thermal evolution of the system; hot protons carry cross‐field thermal energy and cold protons and helium respond to the electrostatic mode and its harmonics respectively. Harmonics of the electrostatic mode are nontrivial in the mixed plasma and contribute substantially to heating in the cold plasma background. Overall, results show evidence of nonlinear processes contributing to particle heating and modulation of excited EMIC waves.

Chorus waves are intense whistler‐mode emissions in space that play a key role in regulating energetic electron dynamics in the hazardous radiation belt. While rising‐tone chorus has been extensively studied, the generation mechanism of falling‐tone chorus remains a long‐standing problem. Using Van Allen Probe A observations, we reveal that falling‐tone chorus in Earth's magnetosphere originates on the downstream side of the magnetic equator along the wave propagation direction, in contrast to the upstream source of rising‐tone chorus. Guided by the typical magnetospheric plasma parameters, we perform the first simulation of falling‐tone chorus in a dipole magnetic field representative of Earth's magnetosphere and reproduce its downstream source region. We further demonstrate that falling‐tone chorus is excited through nonlinear interactions with resonant electrons, where both wave growth and frequency chirping are triggered by resonant currents. Our study fills a critical gap in understanding the nonlinear generation of chorus waves under realistic magnetospheric conditions.

Whistler-mode waves play an important role in electron dynamics within planetary magnetospheres and are ubiquitously observed across a wide range of plasma environments. In Earth's inner magnetosphere, they are commonly classified into incoherent whistler, chorus, and hiss based on their spectral characteristics. This study presents a computational investigation under typical magnetospheric conditions to examine how plasma parameters determine the excitation of different whistler-mode waves. Under low-density conditions outside the plasmasphere, the parameter regimes leading to incoherent whistler, discrete-element chorus, and hiss-like chorus are identified. Peak wave amplitude is quantified for each simulation case, and an empirical relation is established to describe its dependence on hot electron number density and temperature anisotropy. Incoherent whistler waves are driven by linear instabilities of hot electrons, whereas chorus waves arise through nonlinear wave–particle interactions. The growth rates of chorus waves are quantified along the wave packet evolution and are consistent with theoretical predictions. Under high-density conditions within the plasmasphere or plume regions, hiss waves are preferentially generated. This study delineates the parameter regimes for simulating various whistler-mode waves and contributes to a deeper understanding of wave–particle interactions.

It has been proposed that the cyclic rising tone in frequency observed in rising tone quasi-periodic (QP) fast magnetosonic waves is due to the cyclic diffusion of the inner energy edge of the source proton shell distribution toward lower energies. Linear theory shows that as the inner edge of the proton shell diffuses inwards the unstable frequency rises leading to a rising tone. We present the first observations of this diffusion of the proton shell distribution for this type of wave event, observed by the HOPE instrument on Van Allen Probes B, where this diffusion is clearly observed in two back-to-back QP wave cycles. Linear instability is performed on the observed proton shell distribution, and the linear growth rate is compared with the observed wave frequency, the linear theory applied to the observed proton shell distributions was qualitatively but not quantitatively consistent with observed wave frequencies. Nearby Waveform Receiver burst mode measurements showed that the spacing of the emission bands in frequency was very close the proton cyclotron frequency f _cP , suggesting near source. However, a ±2 nT spacecraft induced oscillation at ½ the spacecraft spin period in the background magnetic field magnitude could not allow us to conclude that the emission bands where at integer multiples of f _cP , a stronger condition for source proximity.

It has been proposed that the cyclic rising tone in frequency observed in rising tone quasi‐periodic (QP) fast magnetosonic waves is due to the cyclic diffusion of the inner energy edge of the source proton shell distribution toward lower energies. Linear theory shows that as the inner edge of the proton shell diffuses inwards the unstable frequency rises leading to a rising tone. We present the first observations of this diffusion of the proton shell distribution for this type of wave event, observed by the HOPE instrument on Van Allen Probes B, where this diffusion is clearly observed in two back‐to‐back QP wave cycles. Linear instability is performed on the observed proton shell distribution, and the linear growth rate is compared with the observed wave frequency; the linear theory applied to the observed proton shell distributions was qualitatively but not quantitatively consistent with the observed wave frequencies. Nearby Waveform Receiver burst mode measurements showed that the spacing of the emission bands in frequency was very close to the proton cyclotron frequency f _cP , suggesting a near source. However, a ±2 nT spacecraft induced oscillation at ½ the spacecraft spin period in the background magnetic field magnitude could not allow us to conclude that the emission bands where at integer multiples of f _cP , a stronger condition for source proximity.

Cold protons play an important role in the Earth’s magnetosphere by modifying the dispersion relation of plasma waves. Their energy flux can be enhanced through a nonresonant response to electromagnetic ion cyclotron (EMIC) waves. This study combines Magnetospheric Multiscale (MMS) observations and a hybrid simulation to investigate cold proton dynamics during this nonresonant process. It is found that the energy flux of cold protons with kinetic energies below ~ 200 eV increases due to the bulk flow induced by EMIC waves, and this enhancement becomes stronger and extends to higher energies at higher magnetic latitudes. Despite the flux enhancement, the temperature and number density of cold protons remain constant. Moreover, we identify the formation mechanism of proton phase-bunching distribution in stationary gyrophase. During the nonresonant process, particles bunch in anti-phase with the wave magnetic fields, without exchanging energy with waves. In contrast, during the resonant process, particles bunch in anti-phase with the wave electric fields, facilitating energy transfer from particles to waves. We demonstrate that particle phase-bunching is a necessary but not sufficient condition for identifying resonant interactions with waves, and that the occurrence of energy transfer determines whether the response is nonresonant or resonant. Graphical Abstract

Previous studies indicate that small magnetic flux ropes occupy ∼one third of solar‐wind intervals, yet their appearance in the magnetosheath remains unclear. We use the AuburN Global hybrid CodE in three Dimension (ANGIE3D) to investigate their evolution as they cross Earth's bow shock. We find that the ropes are compressed in the ram direction but retain their transverse dimensions. During shock crossing, backstreaming ions from the trailing edge of the flux rope produce foreshock signatures. In the magnetosheath, significant parallel temperature enhancement occurs within a thin layer on the flux rope's surface. From these results we derive observational signatures to aid identification of interplanetary SFRs in the magnetosheath. These results advance our understanding of coherent‐structure evolution and identification in magnetosheath.