Journal of Geophysical Research: Space Physics最新文献

The Small Payloads for Investigation of Disturbances in Electrojet by Rockets 2 (SPIDER-2) sounding rocket was launched from Esrange, Sweden, on the 19th of February 2020 at 23:14 UT. It traversed a pulsating aurora event, deploying eight free falling units which provided in situ multi-point measurements of the electric field, magnetic field and plasma parameters. In this article, the measured plasma parameters have been analyzed and compared with each other and with optical measurements obtained by ground based instrumentation. Peaks in electron density, thermal ion flux and optical emission have been found in the E region. Electron density profiles have been derived from the data collected by the Langmuir probes in two free falling units, the electron probes in the main rocket and the wave propagation experiment. A generally good agreement has been found among the different measurements in the up-leg of the trajectory, while the effect of the rocket wake was evident in the down-leg. The observed electron density profile has been found to agree with an incoming flux of high energetic electrons with energies around 20 keV. Auroral pulsations with a periodicity of 1–2 s have been recorded by an onboard photometer, a ground-based high speed camera, and the in situ thermal ion flux. The percentages of variation between the ON and OFF phases of the pulsations have been quantified for these quantities. The brightness measured by the photometer varies up to 68%, while the thermal ion flux measurements show only a 2.5% variation.

The inductive component of the magnetospheric electric field, which is associated with the temporal change of magnetic field, provides an additional means of local plasma energization and transport in addition to the electrostatic counterpart. This study examines the detailed response of the inner magnetosphere to inductive electric fields and the associated electric-driven convection corresponding to different solar wind conditions. A novel modeling capability is employed to self-consistently simulate the electromagnetic and plasma environment of the entire magnetospheric cavity. The explicit separation of the electric field by source (inductive vs. electrostatic) and subsequent implementation of inductive effects in the ring current model allow us to investigate, for the first time, the effect of the inductive electric field on the kinetics and evolution of the ring current system. The simulation results presented in this study demonstrate that the inductive component of the electric field is capable of providing an additional source for long-lasting plasma drifts, which in turn significantly alter the trajectories of both thermal and energetic particles. Such changes in the plasma drift, which arise due to the inductive electric fields, further reshape the storm-time ring current morphology and alter the degree of the ring current asymmetry, as well as the timing and the peak of the ion pressure. The total ion energy is increasing at a faster rate than the supply of energetic ions to the ring current, suggesting that the inductive electric field provides effective and accumulative local energization for the trapped ring current population without confining additional particles.

Recent Cluster satellite observations have illustrated that substorm auroral bead formation and currents are associated with the presence of dispersive scale standing Alfvén waves, which are also known as kinetic scale field line resonances (KFLRs) or kinetic Alfvén eigenmodes. In this work, the properties of these waves are further examined using simulations of a gyrofluid-kinetic electron model in conjunction with the Cluster observations at mid-latitudes and Defense Meteorological Satellite Program satellite observations at high-latitudes. These simulations incorporate, for the first time, the effects of both hot magnetospheric and cold ionospheric electron populations within the multi-period evolution of KFLRs. The simulation results demonstrate consistent characteristics with the observed energized electron distributions both at mid- and high-latitudes. Tracing of the energized particle evolution shows that electrons can effectively interact with the wave all along the field line. Quantified energy conversion rates (as determined from $��j_{\Vert }�E_{\Vert }�$) show that significant wave energy dissipation occurs at all latitudes with a maximum occurring in the vicinity of the peak in the profile of the magnetic field to density ratio $��\left(��B�/�n��\right)�$. Additionally, even though dispersive effects lead to the propagation of wave energy across field lines, the particle energization leads to rapid damping of the resonant system in only a few Alfvén periods.

We report on the detection of protons and the potential detection of H₂⁺ between Saturn's F and G rings based on Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) time-of-flight (TOF) composition measurements acquired during Saturn Orbit Insertion (SOI) outbound pass. The range in dipole L shell is 2.3 < L < 2.8. Initial results based on TOF data were presented in E. C. Sittler et al. (2017). Here we present the latest results of our analysis. During the SOI outbound pass between the F and G rings the CAPS IMS was in a mode of reduced post-acceleration voltage at −6 kV instead of the usual −14.6 kV. This reduced voltage still allows the analysis of protons since 6 keV protons are minimally scattered by the instrument's ultrathin carbon foils when compared to heavier ions O⁺ and O₂⁺. Background noise from penetrating radiation and ghost peaks produced by foil-scattered O⁺ ions within the instrument were considered in our analysis. The analysis allowed an determination of the proton density, temperature and flow velocity, accounting for spacecraft potential by assuming a convected Maxwellian for the proton velocity distribution function. We find average proton density n_P = 3.4 ± 1.2 #/cm³, proton temperature T_P = 1.74 ± 0.12 eV, proton corotation flow speed V_P = 24 ± 1.5 km/s in spacecraft reference frame and spacecraft potential Φ_SC = −0.8 ± 1.5 V. These results are compared with previous theoretical estimates of H⁺ and H₂⁺ ions within Saturn's inner magnetosphere.

Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple-band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all-sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground-satellite measurements of three types of subauroral-latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere.

Following the largest magnetic storm in 20 years (10 May 2024), REPTile-2 on NASA's CIRBE satellite identified two new radiation belts containing 1.3–5 MeV electrons around L = 2.5–3.5 and 6.8–20 MeV protons around L = 2. The region around L = 2.5–3.5 is usually devoid of relativistic electrons due to wave-particle interactions that scatter them into the atmosphere. However, these 1.3–5 MeV electrons in this new belt seemed unaffected until a magnetic storm on 28 June 2024, perturbed the region. The long-lasting nature of this new electron belt has physical implications for the dependence of electron wave-particle interactions on energy, plasma density, and magnetic field strength. The enhancement of protons around L = 2 exceeded an order of magnitude between 6.8 and 15 MeV forming a distinct new proton belt that appears even more stable. CIRBE, after a year of successful operation, malfunctioned 25 days before the super storm but returned to functionality 1 month after the storm, enabling these discoveries.

The ionosphere is pivotal for satellite navigation, radio communication, and the modeling of space weather. However, the accurate three-dimensional modeling of ionospheric features remains a challenge. Since solar activity introduces changes in space weather, we collected COSMIC radio occultation observations of 2010–2020 with a suite of indices related to solar and geomagnetic activities, especially including solar EUV and X-ray radiation fluxes, to develop a deep learning model for the global ionospheric electron density. This model, which is called the Solar Flare and Radiation Neural Network (SFRNN) and is based on Embedding, Long Short-Term Memory and fully connected layers, presented excellent performance in reconstructing ionospheric profiles. In this study, 28-min was found to be the best input solar radiation interval for SFRNN with annual RMSEs of 6.24 × 10⁴ to 1.56 × 10⁵ el/cm³. Significantly, during solar flare events, SFRNN had a lower reconstruction error than the former artificial neural network (ANN) model that only uses space weather indices. The most substantial improvement was observed under X-class flares, where SFRNN exhibited a 18.3% lower Root Mean Squared Error than ANN. To further validate the modeling accuracy, electron density profiles derived from Jicamarca incoherent scatter radar (ISR) were used. SFRNN successfully provided profiles with high consistency with the ISR observation in the ionospheric layers. Our modeling results demonstrate that refined solar activity parameters can effectively improve reconstruction performance.

A major challenge in solar-terrestrial physics is to understand the large-scale dynamics of planetary magnetospheres, such as the motion of the Earth's magnetopause. Currently, a combination of in situ measurements and numerical modeling has been used to address this challenge, but no global imaging has been available. The discovery of soft X-rays by the solar wind charge exchange (SWCX) process offers an opportunity to image the emitted X-ray photons. The SMILE mission, due for launch in late 2025, will carry a wide field of view soft X-ray telescope designed to observe emission from the magnetosheath and cusps. As no emission is expected from within the magnetosphere, it is expected that the magnetopause boundary will be observable from changes in X-ray intensity across the boundary. Extracting the 3D magnetopause boundary from the 2D X-ray images is a challenging task and several methods have been developed to model it. One method is to create a 3D emissivity model and adjust its parameters to fit the 2D X-ray image. In this paper, we develop a Cusp and Magnetosheath Emissivity Model (CMEM) and compare its performance to a previous model that did not include the cusps. We find CMEM has an improved fit to emissivity simulations for a wide range of solar wind densities, but that a poor choice of initial parameters can generate unphysical fits in both models. We propose and verify a method to resolve this that uses the upstream solar wind density to constrain some of the initial parameters.

Ultra Low Frequency (ULF) waves play an important role in radiation belt dynamics, modulation of higher frequency wave modes and energetic particle precipitation. We investigate the effects of ULF waves on electron precipitation using a global magnetohydrodynamic (MHD) model and a test particle code. ULF waves are simulated using the Lyon-Fedder-Mobarry (LFM) global MHD model coupled to the Rice Convection Model with solar wind parameters provided as upstream boundary conditions. The MHD fields are used to trace electron trajectories as test particles in the Dartmouth rbelt3d model (Kress et al., 2007, https://doi.org/10.1029/2006JA012218). We simulate the 17 March 2015 storm, the largest geomagnetic storm of Solar Cycle 24 with a Dst of −223 nT, to examine electron precipitation associated with recurring ULF oscillations. The simulation results show that the initial bipolar electric field oscillation observed by Van Allen Probes causes energy dependent electron acceleration and inward radial transport, while the loss cone size increases on the dayside due to magnetopause compression causing precipitation loss across all energies. The subsequent ULF oscillations are more effective in producing precipitation for higher energy electrons that are drift phase bunched due to the initial electric field impulse, with loss continuing to occur on the dusk side where electrons drift in phase with anti-sunward propagating ULF waves.

Sporadic meteors are a significant source of metals in the Earth's atmosphere and ionosphere, and the understanding of the seasonal variations of their strengths can provide valuable insights into the origins and orbits of cosmic dust particles near Earth. This study analyzes meteor echo data collected by an all-sky interferometric meteor radar in Ledong (LD, 18.4°N, 109.0°E) to quantify the strengths of sporadic meteor sources and their seasonal variations. The results indicate that the helion, antihelion, and apex sources are stronger than the north toroidal source, highlighting a concentration of sporadic meteors near the ecliptic plane and fewer near the ecliptic poles. Distinct seasonal variations are observed, with meteor activity peaking in April and September, likely corresponding to periods of increased meteor and dust particle density in Earth's orbit. Moreover, eight meteor showers are identified as significantly influencing the apparent radiant distributions and have comparable strengths with sporadic meteor sources. To enhance the analysis, a monthly radiant weighting system in ecliptic coordinates is developed, enabling precise calculation of source strengths and improved characterization of seasonal variations in radiant distributions. This research advances our understanding of sporadic meteors and their role in Earth's atmospheric processes, providing a foundation for future investigations into cosmic dust dynamics.