Journal of Geophysical Research: Space Physics最新文献

During a special MMS Turbulence campaign, almost 80 min of continuous high resolution burst measurements were downlinked from a traversal across Earth's magnetosheath behind mixed quasi-parallel/perpendicular bow shock conditions. Throughout the magnetosheath, we observed magnetic holes containing intense whistler waves known as “Lion Roars” (LRs). We compared the observed properties of LRs to determine why the whistler waves included higher order harmonics in some magnetic holes but not in others. We refer to the LR events with and without harmonics as “Higher Order Harmonic LRs (HOHLRs)” and “nonharmonic LRs”, respectively. From our observations of the LR events, we found that each wave train featured an electron beam moving at the electron Alfvén speed and parallel to the background magnetic field. We also observed that this electron beam had a stronger phase space density for the LRs near the bow shock. For the HOHLR events, we observed that they exhibited a strong antiparallel Poynting flux and high counts of solitary waves surrounding their corresponding magnetic holes, with some detected solitary waves at the edges of the magnetic hole. Additionally, the fundamental frequencies for the HOHLRs were observed around 0.18–0.23 of the electron cyclotron frequency, $��f_{�c�E�}�$. For the nonharmonic LR events, we observed a strong presence of solitary waves within the confines of their magnetic hole, leading to a population of trapped electrons with a parallel/antiparallel temperature anisotropy, strong $��\delta �E_{\parallel }�$ fluctuations, and Poynting flux flowing in an oblique direction with respect to the background magnetic field. Additionally, the fundamental frequencies of nonharmonic LRs were lower, ranging from 0.11 to 0.18 $��f_{�c�E�}�$.

During a special MMS Turbulence campaign, almost 80 min of continuous high resolution burst measurements were downlinked from a traversal across Earth's magnetosheath behind mixed quasi-parallel/perpendicular bow shock conditions. Throughout the magnetosheath, we observed magnetic holes containing intense whistler waves known as “Lion Roars” (LRs). We compared the observed properties of LRs to determine why the whistler waves included higher order harmonics in some magnetic holes but not in others. We refer to the LR events with and without harmonics as “Higher Order Harmonic LRs (HOHLRs)” and “nonharmonic LRs”, respectively. From our observations of the LR events, we found that each wave train featured an electron beam moving at the electron Alfvén speed and parallel to the background magnetic field. We also observed that this electron beam had a stronger phase space density for the LRs near the bow shock. For the HOHLR events, we observed that they exhibited a strong antiparallel Poynting flux and high counts of solitary waves surrounding their corresponding magnetic holes, with some detected solitary waves at the edges of the magnetic hole. Additionally, the fundamental frequencies for the HOHLRs were observed around 0.18–0.23 of the electron cyclotron frequency, $��f_{�c�E�}�$. For the nonharmonic LR events, we observed a strong presence of solitary waves within the confines of their magnetic hole, leading to a population of trapped electrons with a parallel/antiparallel temperature anisotropy, strong $��\delta �E_{\parallel }�$ fluctuations, and Poynting flux flowing in an oblique direction with respect to the background magnetic field. Additionally, the fundamental frequencies of nonharmonic LRs were lower, ranging from 0.11 to 0.18 $��f_{�c�E�}�$.

The generation of traveling ionospheric disturbances (TIDs) near solar terminators has been predicted, and several studies have reported the detection of TIDs associated with sunrise. However, there are also observations that do not show TID signatures at sunrise. We address this issue by investigating false TID detection at sunrise using total electron content (TEC) data from the global navigation satellite system (GNSS) network over the United States and plasma density measurements from the first Republic of China satellite (ROCSAT-1). The TEC morphology near sunrise, characterized by a rapid TEC increase, creates significant deviations between observed and trend (or filtered) TEC values. The collective pattern of this difference (dTEC) appears as a negative dTEC band aligned with sunrise. While this feature can be interpreted as a signature of large-scale TIDs (LSTIDs), it may also falsely suggest a high occurrence rate of medium-scale TIDs (MSTIDs) when dTEC is used as a detection proxy. However, the negative dTEC band at sunrise is not indicative of LSTIDs because the rapid TEC transition at sunrise is caused by photoionization. This interpretation is supported by the detection of a similar dTEC band at sunrise in model outputs that contain no TID information. Furthermore, the distribution of electron density irregularities derived from ROCSAT-1 showed no evidence of enhanced MSTID activity near sunrise. Therefore, false TID detections near sunrise in GNSS TEC data should not be overlooked.

Earth's outer radiation belt electron flux is highly variable and can be enhanced by over an order of magnitude over timescales less than one day, as observed during the October 2012 storm. Previous studies of this storm (e.g., Reeves et al., 2013, https://doi.org/10.1126/science.1237743) have invoked local acceleration to explain this. However, here, we argue that the observations can instead be explained by fast inward radial transport. One method often invoked to distinguish between these two acceleration processes is the existence of local peaks in electron phase space density (PSD) as a function of L* at fixed first, M, and second, K, adiabatic invariants. However, this method relies on the assumption that the evolution of the PSD as a function of L* occurs over timescales slower than the satellite orbital period. Here, high spatiotemporal resolution data from the Global Positioning System (GPS) spacecraft constellation is used to show that enhancements in the PSD occur during the October 2012 storm over short timescales not resolvable by the Van Allen Probes. In addition, Geostationary Operational Environmental Satellite spacecraft data also indicate that these enhancements are consistent with relativistic electron injections. A radial diffusion model is shown to reproduce the PSD dynamics observed by the Van Allen Probes, once rapid variations at the simulation outer boundary are included, consistent with GPS data. This verifies that apparently “locally growing” peaks in PSD along high apogee satellite orbits can be produced by fast inward radial transport without requiring the action of any local acceleration processes.

In this work, we investigate co-seismic ionospheric disturbances (CSIDs) generated by the M8.8 earthquake of 29 July 2025 east of Petropavlovsk-Kamchatsky, Russia. By combining Ionosonde, global navigation satellite system slant TEC (sTEC) measurements, seismic waveforms, and time-distance (TTD) analysis, we track earthquake-induced perturbations across five azimuthal sectors extending from the western Pacific to the American west coast. We detected CSIDs with velocity 2.95–3.23 km/s linked to Rayleigh surface waves and associated acoustic waves, with Rayleigh-wave velocities of 3.46–3.87 km/s. Multiple-cusp signatures are identified on ionograms, indicative of vertical electron density perturbations associated with Rayleigh waves. Tracking nodes of these MCS perturbations across consecutive profiles yield apparent vertical velocities of 411–880 m/s, providing approximate constraints on upward propagation. sTEC-derived CSID velocities show good agreement with MCS-inferred speeds, ranging from 2.42 to 3.91 km/s, while delays of 8–18 min relative to Rayleigh-wave arrivals reflect acoustic coupling and ionospheric propagation. This study highlights the anisotropic propagation of earthquake-driven ionospheric disturbances and underscores the value of a multi-instrument approach in resolving both horizontal and vertical dynamics of CSIDs.

During the Mother's Day Storm, the most intense storm of the last 20 years, with a peak Dst of less than −400 nT, the Macau Science Satellite-1 observed the penetration of relativistic electrons of energies greater than 1 MeV into the inner radiation belt at Low Earth Orbit (LEO). The arrival of the MeV electrons was observed to occur instantaneously following the Dst minimum, with their continuous enhancement in the South Atlantic Anomaly over 7 days in the recovery phase reaching L $��=�$ 1.5. The so-called impenetrable barrier, previously estimated to be located at L $��=�$ 2.8 during the Van Allen Probes' era, has been significantly violated. A combined analysis of observations with Arase data at mid-latitude reveals the evolution of electron spectrum and pitch angle distribution for the first time, including zebra stripe patterns, an increase in electron flux near the loss cone, and a decrease in electron flux at higher pitch angles. These new results suggest that MeV electrons might undergo several steps to reach the inner radiation belt at LEO during this storm, which includes radial transport, radial diffusion, local acceleration and pitch angle scattering.

The location and stability of the dayside X-line at the magnetopause are two fundamental properties of the process that dominates solar-terrestrial interactions. Various investigations using simulations and theory concluded that the location of the dayside X-line is not stable in physical space but convects away from the subsolar region in the direction of the plasma bulk velocity in the magnetosheath. This study investigates the stationarity, or stability, of the dayside reconnection X-line using MMS observations. The X-line encounters are identified by ion beam switches. For a given beam switch time series, it is assumed that the first or initial ion beam direction observed by the satellites during a magnetopause crossing indicates the direction the X-line convects. The ratio of X-lines moving toward or away from the subsolar region is about equal. No preference of the X-line drift in the direction of the bulk velocity in the magnetosheath could be found. In about half of the cases, the X-line moves against the magnetosheath flow direction and toward the subsolar region. In addition, about 40% of the events show multiple crossings of a single X-line. These multiple crossings in short succession suggest that the X-line oscillates around the primary reconnection location.

In this work, we investigate co-seismic ionospheric disturbances (CSIDs) generated by the M8.8 earthquake of 29 July 2025 east of Petropavlovsk-Kamchatsky, Russia. By combining Ionosonde, global navigation satellite system slant TEC (sTEC) measurements, seismic waveforms, and time-distance (TTD) analysis, we track earthquake-induced perturbations across five azimuthal sectors extending from the western Pacific to the American west coast. We detected CSIDs with velocity 2.95–3.23 km/s linked to Rayleigh surface waves and associated acoustic waves, with Rayleigh-wave velocities of 3.46–3.87 km/s. Multiple-cusp signatures are identified on ionograms, indicative of vertical electron density perturbations associated with Rayleigh waves. Tracking nodes of these MCS perturbations across consecutive profiles yield apparent vertical velocities of 411–880 m/s, providing approximate constraints on upward propagation. sTEC-derived CSID velocities show good agreement with MCS-inferred speeds, ranging from 2.42 to 3.91 km/s, while delays of 8–18 min relative to Rayleigh-wave arrivals reflect acoustic coupling and ionospheric propagation. This study highlights the anisotropic propagation of earthquake-driven ionospheric disturbances and underscores the value of a multi-instrument approach in resolving both horizontal and vertical dynamics of CSIDs.

Loss of relativistic electrons with energies above 0.5 MeV through the magnetopause, commonly referred to as magnetopause shadowing, has been extensively investigated using both simulations and observations. However, direct and systematic observational evidence remains limited. In this study, we extend a previously developed magnetopause model by incorporating inward magnetopause motion, which generates induced electric fields within the boundary layer. These fields are amplified during compression and further enhanced by magnetic field strengthening on the magnetospheric side. Relativistic electrons (0.5–a few MeV) are influenced by the induced fields primarily through gyroradius reduction caused by energy loss and through $��\overrightarrow{E}�\times �\overrightarrow{B}�$ drift toward the magnetosphere, both of which inhibit escape. Stronger electric fields extend the energy range of confined electrons toward higher energies. Depending on the local field geometry, the induced electric field can either accelerate or decelerate electrons. In contrast, ultra-relativistic electrons (several MeV), with gyroradii comparable to the magnetopause thickness, are less affected and more likely to escape directly. When a finite magnetic field component normal to the magnetopause is present, electrons across a broad energy range (0.5–10 MeV) can escape efficiently, as this component guides their motion across the boundary and reduces sensitivity to the induced field. In such cases, energy variations still occur but become less significant with increasing normal component strength, owing to shorter residence times within the magnetopause.

Quasi-thermal noise (QTN) spectroscopy is a plasma diagnostic technique that enables precise measurements of moments for the local electron velocity distribution function. Previous studies on the QTN technique applied to weakly ionized collisional plasma were limited by the assumptions of unmagnetized and Maxwellian distributions. In this paper, we extend prior research by considering collisional and a secondary hot Maxwellian distribution. Further analysis indicates that as the collision frequency increases, the peak power spectral density at the $��\text{electron}��\text{plasma}��\text{frequency}��f_p�$ decreases. In addition, we find that the influence of collisions on low-frequency cyclotron harmonic signals in a magnetized plasma is mainly related to the plasma-to-electron cyclotron frequency ratio $��{\omega }_{\text{pe}}�/�{\Omega }_{\text{ce}}�$, but also has non-trivial dependencies on the plasma Debye Length $��L_D�$. Finally, we observed that in eight representative cases, the plasma harmonic disappearance frequency ratio is generally ∼0.25. Our research provides valuable theoretical guidance for the future application of QTN techniques in detecting plasma parameters, especially for collision frequencies typical of Earth's ionosphere.