Journal of Geophysical Research: Space Physics最新文献

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.

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.

Predicting times of arrival and properties of space weather events, such as coronal mass ejections and stream interaction regions (SIRs), has become an important focus of the space physics community within recent years. Extensive efforts have been undertaken to model these space weather events throughout the heliosphere in order to better understand their properties and predict how and when they will impact planetary environments. In this study, we compare in situ solar wind parameters during SIRs measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft to parameters generated by the Wang-Sheeley-Arge (WSA)-ENLIL stationary solar wind model. We compare times of arrival, end times, event duration, solar wind parameters, and magnetic compression ratios as measured by MAVEN versus WSA-ENLIL using a previously compiled 9-year catalog of SIR observations. We find that WSA-ENLIL, on average, predicts earlier times of arrival and longer duration SIRs than what is observed by MAVEN. We examine how in situ solar wind parameters compare to those predicted by WSA-ENLIL and find that solar wind proton density and magnetic field magnitude are slightly underpredicted by the model, while solar wind speed is well predicted. We also find that the magnetic compression ratio predicted by WSA-ENLIL is higher than MAVEN by an average of $��\sim �$26%. We examine the effects of planetary geometry on the modeling outputs and find that certain parameters are more adversely impacted than others depending on the alignment of Earth and Mars.

The polar cap ionosphere is a dynamic and intricately structured environment that plays host to polar cap patches (PCPs) and other mesoscale density formations. These phenomena can lead to the emergence of smaller-scale structures through various plasma instability mechanisms. Existing literature highlights substantial variability in the occurrence, density, and characteristics of PCPs influenced by solar and geomagnetic conditions. However, a comprehensive statistical analysis utilizing long-term data is lacking, particularly from the Resolute Bay Incoherent Scatter Radar North (RISR-N). In this article, we consider 11 years of RISR-N data (≅one solar cycle) to perform an analysis of PCPs, focusing on their occurrence distributions, behavior with density, temperature, different geomagnetic indices, and characteristics over time. We show the long-term distribution of PCPs and how it varies with geomagnetic activity. We examine the role of solar activity by investigating correlations between solar activity indices (e.g., F10.7, solar wind conditions) and the occurrence of PCPs to provide a clearer picture of the influence of solar activity on patch dynamics. We identify seasonal and diurnal variability of PCPs to establish a clear understanding of how these factors influence their behavior.