Journal of Geophysical Research: Space Physics最新文献

Prior studies identified a fine structure in the middle latitude ionosphere known as the strip-like plasma density bulge. These bulges emerge during geomagnetic storms, exhibiting a broad longitudinal span of over 150° and a narrow latitudinal extent of 1°–5°. The observations from the DMSP and ICON satellites reveal stronger equatorward ion drifts and neutral winds on the poleward side of bulges compared to the equatorward side. Using the Sami2 is Another Model of the Ionosphere (SAMI2), the bulge feature was reproduced for the storm of 4∼6 November 2021 by amplifying the default meridional winds. Numerical simulations indicate that global wind disturbances establish a sharp meridional wind gradient within the lower mid-latitude region. This gradient, in turn, drives a divergence in ion transport parallel and perpendicular to the magnetic field lines, which ultimately results in the localized accumulation of plasma. The phenomenon is most pronounced in the vicinity of ±30° quasi-dipole latitude. This region is characterized by a magnetic inclination angle of approximately 45°, a configuration where the meridional wind component acts most efficiently to elevate ions vertically.

We report in situ evidence for Enceladus' Alfvén wing system and its coupling with Saturn's ionosphere, based on multi-instrument observations from the Cassini spacecraft. Analysis of 36 events, including 13 from non-flyby paths, confirms the existence of a Main Alfvén Wing (MAW) current system generated at Enceladus, and associated Reflected Alfvén Wings (RAWs) occurring both at Saturn's ionosphere and on the density gradient of Enceladus' plasma torus, extending longitudinally to at least $��\sim �120�°�$ ($��\sim �$2,000 moon radii) downstream of the moon. Additionally, the observations reveal the systematic existence of a filamentation process of these large-scale Alfvénic perturbations (MAW and RAWs) during their propagation at any distance from their source. These findings demonstrate a more extensive electrodynamic coupling than previously reported for Enceladus and more generally for any moon-magnetosphere interaction. Moreover, the observation of energetic electron depletions and water-group ion signatures at longitudes even further from the moon supports the interpretation of an extended and persistent interaction region. These results highlight Enceladus' role in shaping Saturn's magnetospheric environment and underscore the importance of future missions to exhaustively analyze this type of complex interaction between a moon and a planet.

The study reports a long-lasting nighttime TEC (Total Electron Content) enhancement and the violent outburst of scintillations in response to the recovery phase of the May 2024 Superstorm over the northeast Asian sector using comprehensive observations mainly from the Shandong Peninsula of China and the madrigal GPS TEC in global. Since ∼11:30 UT on 11 May 2024 of the geomagnetic superstorm, a unique nighttime TEC enhancement (above 40 TECU) appeared in Northeast Asia with almost double TEC values than that in the quiet condition, which is lasting more than 12 hr. It is interesting to emphasize that the nighttime TEC enhancement drifted westward overall from Japan to the west of China. Moreover, a sharp escalation of phase and amplitude scintillation indices (>0.4) has been captured at Weihai since ∼20:00 UT at 11 May 2024, which is coincident with the arrival of spread F precisely along with the nighttime TEC enhancement very likely. In contrast, normally, the scintillation indices just fluctuate around 0.1, in which the amplitude scintillation index is slightly greater than the phase scintillation index in general. Therefore, the findings detail the responses to 2024 May superstorm at mid-latitudes of Northeast Asia, deepening the recognization on space weather effects.

Electron cyclotron harmonic (ECH) waves, a subset of electron Bernstein modes, are characterized by their distinct harmonic frequency structures. In the outer magnetosphere of the Earth, these waves play a vital role in electron scattering, pitch-angle diffusion, and the subsequent precipitation of particles into the ionosphere. In contrast, their properties in the vicinity of the Lunar surface remain relatively poorly understood. In this study, we investigate the statistical characteristics of ECH waves using 8 years of observations from the ARTEMIS mission, with the objective of systematically characterizing their behavior across diverse Lunar plasma environments. Our analysis indicates that the overall occurrence rate of ECH waves within the region $��r�\le �12�R_L�$ is approximately 0.099%, but this rate rises to more than 1% on the anti-sun side in close proximity to the Moon. Moreover, the majority of ECH wave events are detected when the Moon resides within the Earth's magnetotail. On the anti-sun side, enhanced ECH wave amplitudes are most pronounced in the near Lunar surface region. These results demonstrate that the local Lunar plasma environment strongly influences ECH wave activity, with Lunar magnetic field anomalies significantly modulating the occurrence rate of ECH waves while exerting no substantial influence on their amplitude. Collectively, these findings provide new insights into the plasma processes operating near the Lunar surface.

The formation process of the F3 layer at sunrise in the middle latitudes is newly investigated using data from the Mother's Day geomagnetic storm of 10–11 May 2024. Ionosonde, Fabry-Perot Interferometer (FPI), satellite data, and model simulations of Equatorial Electric Field for India, South-East Asia-Australia, and Japanese sectors are utilized. The F3 layer was recorded by Ionosondes at Japanese mid-latitude stations during 19 UT–21 UT, which coincided with the local Sunrise time. Over Perth (Australia), Wuhan (China), and Ahmedabad (India), formations were delayed at 22 UT–23 UT. The COSMIC vertical profiles showed enhanced F2 layer altitude after 19 UT, and confirmed the formation of additional ionospheric stratifications above the F2 layer. The thermospheric winds measured by FPI at northern mid-latitude and southern low-latitudes indicated strong equatorward winds in both hemispheres starting around 18:30 UT. The analysis revealed that dawn-time F3 layer stratifications in middle latitude were manifestations of residual nighttime F layer, which was raised to higher altitude by the equatorward winds, even as a new weak F2 layer was formed below by photo-ionization. The reduction in thermospheric O/N₂ caused the F3 layer at higher altitudes to survive and remain stronger than the F2 layer for a considerable time after sunrise. In contrast, the low-latitude F3 layer was formed by vertical drift induced by the electric field, when an IMF-Bz transition resulted in an eastward penetration electric field pulse in the dawn sector. At Perth in the southern hemisphere, both mechanisms were effective in the formation (wind) and sustenance (electric field) of the F3 layer.

The F10.7 and F30 solar indices are the solar radio fluxes measured at wavelengths of 10.7 and 30 cm, respectively, which are key indicators of solar activity. F10.7 is valuable for explaining the impact of solar ultraviolet (UV) radiation on the upper atmosphere of Earth, while F30 is more sensitive and could improve the reaction of thermospheric density to solar stimulation. In this study, we present a new deep learning model, named the Solar Index Network, or SINet for short, to predict daily values of the F10.7 and F30 solar indices. The SINet model is designed to make medium-term predictions of the index values (1–60 days in advance). The observed data used for SINet training were taken from the National Oceanic and Atmospheric Administration as well as Toyokawa and Nobeyama facilities. Our experimental results show that SINet performs better than five closely related statistical and deep learning methods for the prediction of F10.7. Furthermore, to our knowledge, this is the first time deep learning has been used to predict the F30 solar index.

We investigate the injection and transport of energetic particles from the Earth's plasma sheet into the inner magnetosphere during the three consecutive substorms that occuurred on 7 September 2017. Using coordinated observations from the MMS, LANL, and Van Allen Probes spacecraft, we track the evolution of ion and electron fluxes from the mid-tail to the inner magnetosphere. Using the dipole field approximation to trace particle drift orbits from LANL satellites at geosynchronous orbit, we identified the equatorial injection region to extend from ∼2000 to ∼0400 MLT. Subsequently, the injected particles were detected further earthward at Van Allen Probes (L ∼ 4), particularly on the dayside. The multi-point data reveal that stronger substorms injected ions over a wide energy range (1–200 keV) with significant dayside penetration, while weaker substorms resulted in narrower energy injections (5–30 keV). Back-tracing the proton drift paths further, calculated using the electric and magnetic fields from the MHD simulation, indicates that convection and adiabatic drifts alone are insufficient to account for the ion injections observed at the Van Allen Probe locations. This suggests that non-adiabatic processes, such as substorm-driven impulsive electric fields, are required for particles to reach the same regions. In contrast, electrons at Van Allen Probes lacked clear injection signatures, suggesting the influence of localized electric fields. These results highlight the spatiotemporal complexity of substorm injections and emphasize the value of multi-point observations and simulations to understand particle transport in the inner magnetosphere.

We propose an approach to simulate ultra-wideband (UWB) electromagnetic pulse (EMP) propagation in the ionosphere with magnetic field-aligned irregularities of plasma density based on Monte Carlo technique. This approach considers propagation of a nanosecond EMP by ray trajectories in the frequency domain, which allows one to analyze the role of scattering effects for lower and higher harmonics of the pulse. Parameters of the irregularities used in the simulations are chosen close to those of artificial ionospheric turbulence (AIT) density striations stimulated by high-frequency (HF) heating facilities. The employed technique provides a possibility to compare the effects of dispersion and scattering on the waveform of bipolar nanosecond EMP for various parameters of ionospheric plasma and its disturbances. In the presence of 10-m scale, 10-percent level density striations, we show that lower frequencies are most responsible for the EMP waveform transformation due to the plasma dispersion, and are scattered away from the initial propagation direction, while higher frequencies experience minor dispersion and are less scattered. The influence of AIT-type striations on the straightforward EMP delay and its broadening in the time domain is analyzed compared to the EMP propagation in uniform plasma. Preliminarily, the effects of AIT-type striations on EMP characteristics seem to be weak in the main part of its frequency spectrum, even for strong (non-realistic) plasma density depletions of up to 50%.

Geomagnetic indices can be used to quantify variations in geomagnetic activity caused by Sun-Earth interactions across the magnetosphere and ionosphere. The global Kp index is widely used as a global geomagnetic indicator, but it is based mostly on the Northern Hemisphere with no contributions from South American observatories. As a result, regional features such as the South American Magnetic Anomaly (SAMA) are not represented. To address this limitation, the regional Ksa index was developed using magnetometer data collected from the Embrace Magnetometer Network (Embrace MagNet), which consists exclusively of South American stations. This study analyzes data from Ksa and Kp and introduces two additional hybrid indices, Kp* and Ksa*. The Kp* index uses global data from the International Real-time Magnetic Observatory Network processed with the Embrace MagNet algorithm, while the Ksa* index applies the Finnish Meteorological Institute algorithm to South American data. The analysis was conducted over the year 2020, a period characterized by low solar activity, to investigate the behavior of the indices under quiet conditions during three seasonal periods: December solstice, Equinoxes, and June solstice. Pearson correlation coefficients were computed to evaluate the relationships between the indices. The results revealed significant discrepancies between indices derived from different data sets, even when processed with the same algorithm. These differences emphasize the impact of regional geomagnetic phenomena such as the SAMA and Sq current variability.

State parameter profiles in the equatorial topside ionosphere were measured in June, 2023, and late July and early August, 2025, at the Jicamarca Radio Observatory. The measurements combined multiple radar pulsing schemes and analysis methods. In 2025, for the first time, plasma drifts were measured concurrently with electron densities, electron and ion temperatures, and ion composition by exploiting a new electronic beam steering capability. Significant quiet-time day-to-day variability is evident across all measurements. In this study, variability in the vertical drifts is considered as a source of variability in the other plasma state parameters. Topside temperatures and the midday temperature depression in particular are examined for sensitivity to vertical drifts. While predictions obtained from the SAMI2-PE model, which includes energetic electron transport, exhibit reasonable agreement with observations overall, they do not account for topside variability. Some limitations of the measurements and the model along with strategies for improvement and further study are discussed.