This paper reports a dispersion analysis of two wave packets simultaneously observed near the local proton gyrofrequency by the Parker Solar Probe. The observed wave event exhibits clear two-banded wave packets both propagating along the magnetic field, characterized by left-handed (L-mode) and right-handed (R-mode) polarizations simultaneously. By incorporating the Doppler shift effect into a linear dispersion analysis, we find two possible scenarios that explain these simultaneous opposite polarizations: (1) Two inherently L-mode waves in the plasma frame, propagate parallel and antiparallel to the solar wind velocity, with similar wave frequencies and wave numbers. The polarization of the antiparallel propagating wave reverses as it moves sunward in the plasma frame while still comoving with the solar wind in the stationary frame. This reversal manifests the polarization of the wave as an R-mode in the spacecraft frame. (2) Simultaneous L-mode and R-mode waves propagate parallel to the solar wind velocity, with different wave frequencies and wave numbers. Concurrent proton observations during the wave event reveal a dominant anisotropic ( T ⊥ / T ∥ > 1 ) core distribution with a drifting beam population. Estimation of the linear growth rate for both L-mode and R-mode waves suggests that both scenarios are plausible, indicating that the observation is near the wave-generation region. We explore the potential impact of these simultaneous waves on solar wind heating and scattering effects, hypothesizing that such waves might enhance efficiency compared to waves with a single wave packet, contingent upon the statistical significance of such waves.

Electromagnetic ion cyclotron (EMIC) waves, driven by ring current ion temperature anisotropy in the Earth's magnetosphere, play a key role in accelerating and precipitating relativistic electrons in the radiation belts. Their excitation and saturation are significantly affected by the surrounding cold plasma. Previous studies have shown that background cold helium ions can influence the growth and saturation of EMIC waves, yet the role of cold oxygen ions in wave saturation remains less understood. In this paper, we use linear theory and nonlinear hybrid simulation to investigate the effect of cold oxygen ions in the EMIC wave growth and saturation in a homogeneous plasma containing hot and cold protons, cold helium and cold oxygen ions. Our findings reveal that increasing the cold oxygen ion concentration decreases the EMIC wave growth rate and broadens the spectral width of stop bands near the helium and oxygen gyrofrequencies. Furthermore, an increasing oxygen ion concentration notably reduces the saturation amplitude of EMIC waves in cases where the helium band is dominant, while cases with a dominant hydrogen band remain unaffected. Cold ions are heated during wave excitation, and cold helium ions are heated to keV energy, more significantly than cold protons and oxygen ions. With cold oxygen ion concentration increasing, cold helium ions take longer time to be heated to keV energy. These results offer insights into how cold plasma modifies the spectral properties and amplitudes of EMIC waves, shedding light on energy transfer from hot protons to cold plasma through EMIC waves.

We compared the performance of DREAM3D simulations in reproducing the long-term radiation belt dynamics observed by Van Allen Probes over the entire year of 2017 with various boundary conditions (BCs) and model inputs. Specifically, we investigated the effects of three different outer boundary conditions, two different low-energy boundary conditions for seed electrons, four different radial diffusion (RD) coefficients (DLL), four hiss wave models, and two chorus wave models from the literature. Using the outer boundary condition driven by GOES data, our benchmark simulation generally well reproduces the observed radiation belt dynamics inside L* = 6, with a better model performance at lower mu than higher mu, where mu is the first adiabatic invariant. By varying the boundary conditions and inputs, we find that: (a) The data-driven outer boundary condition is critical to the model performance, while adding in the data-driven seed population doesn't further improve the performance. (b) The model shows comparable performance with DLL from Brautigam and Albert (2000, ), Ozeke et al. (2014, ), and Liu et al. (2016, ), while with DLL from Ali et al. (2016, ) the model shows less RD compared to data. (c) The model performance is similar with data-based hiss models, but the results show faster loss is still needed inside the plasmasphere. (d) The model performs similarly with the two different chorus models, but better capturing the electron enhancement at higher mu using the Wang et al. (2019, ) model due to its stronger wave power, since local heating for higher energy electrons is under-reproduced in the current model. Relativistic electrons in the outer radiation belt are very dynamic involving various acceleration and loss processes under the influence of radial diffusion (RD), hiss, and chorus waves. The physical processes are regarded as diffusive in behavior. The DREAM3D code solves the Fokker-Plank equation to investigate the radiation belt dynamics in the aspect of the diffusive dynamics of electrons. A variety of empirical models and boundary conditions have been developed and included in the simulations in the literature. In this study, we compare the DREAM3D performance in reproducing the observed radiation belt dynamics with various empirical models of the RD coefficients, hiss and chorus wave, and boundary conditions. In conclusion, we find the data-driven outer boundary condition is very important to reproduce the observed radiation belt variations. For the RD coefficients, all DLL exhibit comparable performances while DLL from Ali et al. (2016, ) shows slower RD due to its smaller magnitude. All the hiss wave models lead to effective loss inside the plasmasphere, but stronger losses are needed. For the chorus wave models, the two models are comparable with a small difference in model performance due to the different levels of wave power. This work compares the performance of long-term radiation belt simulations using various inputs and boundary conditions Using GOES outer boundary condition, the benchmark simulations reproduce the radiation belt dynamics inside L* = 6 observed by Van Allen Probes The data-driven OB condition is critical to the model performance, and stronger loss inside the plasmasphere could improve the performance

AbstractProton cyclotron waves (PCWs) upstream of Mars are thought to be associated with the instabilities of pickup ions. The instabilities of pickup ions of ring distributions have larger maximum growth rates compared with beam distributions. However, observations revealed a notably‐reduced occurrence rate of PCWs for pickup ions of ring distributions. Linear instability analysis and a corresponding two‐dimensional particle‐in‐cell (PIC) simulation are performed to investigate the instabilities of pickup ion ring distributions upstream of Mars. Linear instability analysis indicates that a pickup ion ring distribution is unstable to the ion cyclotron, ion Bernstein, and mirror instabilities. The corresponding PIC simulation confirms the linear analysis results and further demonstrates that the pickup ions are scattered toward an isotropic shell distribution by the waves excited. Interestingly, the saturation energy of the waves is much lower than that driven by a corresponding pickup ion beam distribution, and mirror waves eventually dominate the system.

Recognition for All: A Way Forward to Enhance Diversity, Equity and Inclusion in Space Physics M. Fraz Bashir,1 Amy M. Keesee,2, 3 Seth G. Claudepierre,4 Michael D. Hartinger,5 Elizabeth A. MacDonald,6 and Allison Jaynes7 Department of Earth, Planetary and Space Sciences, UCLA, Los Angeles, CA, USA∗ Department of Physics and Astronomy, University of New Hampshire, Durham, NH, USA Space Science Center, University of New Hampshire, Durham, NH, USA Department of Atmospheric and Oceanic Sciences, UCLA, Los Angeles, CA, USA Center for Space Plasma Physics, Space Science Institute, Boulder, CO, USA NASA Goddard Space Flight Center, Greenbelt, MD, USA Department of Physics Astronomy, University of Iowa, IA, USA

EDITORIAL article Front. Astron. Space Sci., 22 February 2023Sec. Space Physics Volume 10 - 2023 | https://doi.org/10.3389/fspas.2023.1149649

Abstract Linear instability analysis as well as a corresponding two‐dimensional hybrid simulation are performed to examine the excitation of the proton cyclotron waves observed upstream of Mars. The waves are believed to be excited by the pickup ions produced from the ionization of the Martian hydrogen exosphere. And previous statistical analysis of wave observations suggested that the waves are mostly related to pickup ion beam velocity distributions. While earlier linear instability analysis of pickup ion beam distributions has mainly been focused on the parallel unstable modes, our analysis reveals that the maximum growth rate occurs at very oblique propagation. The corresponding hybrid simulation confirms the linear analysis results and further demonstrates that the pickup ions are scattered toward an isotropic shell velocity distribution by the waves excited. Interestingly, the waves at oblique propagation gradually damp out and the system is eventually dominated by waves of quasi‐parallel propagation.

The laminar coupling of energy between a laser-produced plasma and a background magnetized plasma was investigated via planar laser induced fluorescence diagnostic and magnetic flux probes. Experiments performed on the Large Plasma Device at the University of California, Los Angeles, mapped out the two-dimensional spatiotemporal evolution of the laser-plasma (debris) ion velocity distribution function (VDF) to assess debris-background coupling in a sub-Alfvénic regime. The acquisition of these data necessitates high repetition rate (1 Hz) as each dataset is the accumulation of thousands of laser shots, which would not be feasible in single-shot experiments. Fully kinetic, three-dimensional particle-in-cell simulations are compared to the measured VDFs to provide a framework in which we can understand the coupling of a sub-Alfvénic plasma flow through a preformed, magnetized plasma. The simulations display the same departure from the expected gyromotion of the debris plasma as observed in the experimental data, and in conjunction with the measured magnetic field traces, have led to the direct observation of the collisionless coupling via laminar fields.

Various systems can be modeled as a point-like explosion of ionized debris into a magnetized, collisionless background plasma – including astrophysical examples, active experiments in space, and laser-driven laboratory experiments. Debris streaming from the explosion parallel to the magnetic field may drive multiple resonant and non-resonant ion-ion beam instabilities, some of which can efficiently couple the debris energy to the background and may even support the formation of shocks. We present a large-scale hybrid (kinetic ions + fluid electrons) particle-in-cell (PIC) simulation, extending hundreds of ion inertial lengths from a 3-D explosion, that resolves these instabilities. We show that the character of these instabilities differs notably from the 1-D equivalent by the presence of unique transverse structure. Additional 2-D simulations explore how the debris beam length, width, density, and speed affect debris-background coupling, with implications for the generation of quasi-parallel shocks.

The coupling between a rapidly expanding cloud of ionized debris and an ambient magnetized plasma is revisited with a hybrid (kinetic ion/fluid electron) simulation code that allows a study over a wide range of plasma parameters. Over a specified range of hypothetical conditions, simple scaling laws in terms of the total debris mass and explosion speed are derived and verified for the maximal size of the debris cloud and the fraction of debris that free-streams from the burst along the magnetic field. The amount of debris that escapes from the burst with minimal coupling to the background magnetic field increases with the debris gyroradius. Test cases with two different debris species--including a heavy minority species with a relatively large gyroradius--highlight how the collisionless coupling of the debris depends on the single-particle trajectories as well as the overall conservation of energy and momentum.

During geomagnetic storms, the ring current ions sometimes exhibit rapid loss as suggested by the fast recovery of the Dst index on a time scale of a few hours. The effects of magnetic field line curvature (FLC) scattering on the loss of ring current ions, which have not been well quantified, are studied here by test particle simulations under the T89c magnetic field model. Our simulation results show that the prediction of ion loss based on a single-value cutoff of the kappa parameter or maximum of delta mu/mu of a single FLC scattering is not accurate. Instead, the e-folding lifetime (tau) for the loss of ring current ions due to cumulative FLC scattering has been calculated for different initial ion energies, equatorial pitch angles, and L shells under different geomagnetic conditions. The results show that in general the FLC scattering loss is faster for ions of higher energy, higher mass, smaller pitch angle, higher L, and at high Kp level. Specifically, we find that at Kp = 6 the lifetime can be L > 5 for 100 s keV protons and at L > 4 for 100 s keV O+, which demonstrates that FLC scattering can be an important mechanism for the observed fast loss (tau < 10 h) of ring current ions during geomagnetic storms. Furthermore, we formulate an empirical formula for tau as a function of ion energy, pitch angle, position, species, and Kp. The empirical formula can be directly included in ring current models to account for the FLC scattering effects.

Saturn's largest icy moon, Rhea, hosts a tenuous surface-sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea and confirm that Cassini detected nongyrotropic fluxes of outflowing CO2+ during both the R1 and R1.5 encounters. Accounting for this nongyrotropy, we show that these possess comparable along-track densities of similar to 2x10(-3) cm(-3). Negatively charged pickup ions, also detected during R1, are surprisingly shown as consistent with mass 26 +/- 3 u which we suggest are carbon-based compounds, such as CN-, C2H-, C-2(-), or HCO-, sputtered from carbonaceous material on the moon's surface. The negative ions are calculated to possess along-track densities of similar to 5x10(-4) cm(-3) and are suggested to derive from exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO2 exosphere and surprisingly low O-2 sputtering yields. These pickup ions provide important context for understanding the exospheric and surface ice composition of Rhea and of other icy moons which exhibit similar characteristics.

Saturn's largest icy moon, Rhea, hosts a tenuous surface-sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea to show that Cassini detected nongyrotropic fluxes of outflowing CO$_2^+$ during both the R1 and R1.5 encounters. Accounting for nongyrotropy, we show that these possess comparable alongtrack densities of $\sim$2$\times$10$^{-3}$ cm$^{-3}$. Negatively charged pickup ions, also detected during R1, are shown as consistent with mass 26$\pm$3 u which we suggest are carbon-based compounds, such as CN$^-$, C$_2$H$^-$, or C$_2^-$, sputtered from carbonaceous material on the moons surface. The negative ions are calculated to possess alongtrack densities of $\sim$5$\times$10$^{-4}$ cm$^{-3}$ and are suggested to derive from implanted exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO$_2$ exosphere and surprisingly low O$_2$ sputtering yields. These pickup ions provide important context for understanding Rhea's exospheric and surface-ice composition as well as of other icy moons which exhibit similar characteristics.