Journal of Geophysical Research: Space Physics最新文献

The extension of the post-sunset equatorial plasma bubbles (EPBs) to mid-latitudes during geomagnetic storms has been widely reported. However, previous research has primarily focused on the initiation and spatial distribution of these EPBs, while their decay processes remain underexplored. In this study, we provide observations of the evolution and dissipation of intense EPBs during the geomagnetic storm on 23–24 April 2023, using measurements from the Global-scale Observations of the Limb and Disk (GOLD), Swarm, and COSMIC-2 satellites. During the storm main phase, intense EPBs with zonal extents of ∼2–3° and latitudinal extents reaching up to ±35° magnetic latitude (Mlat) were observed between 15°W and 5°W. Simultaneously, very low electron density regions, spanning approximately from ±30° to ±45° Mlat and 420–500 km in altitude, were observed in the mid-latitudes. During the storm, the EPBs were observed to extend gradually poleward and subsequently encountered the low electron density regions. This encounter process, along with the storm-caused electric field dynamics, led to a gradual weakening and diffusion of the EPBs. The airglow images from GOLD showed that EPBs evolved from coherent depletions into structurally diffused forms with embedded filamentary features and eventually merged into the background. Notably, a hemispheric asymmetry in EPB dissipation was observed. In the Northern Hemisphere, EPBs tended to retain their morphology for a longer time, while in the Southern Hemisphere, more rapid dissipation occurred, likely due to differing background plasma conditions and magnetic field configurations in the two hemispheres. These findings reveal a previously uncharacterized feature of EPB dissipation during geomagnetic storms.

Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) have long been a subject of interest in ionospheric research. However, their spatiotemporal variability across regions, local times, seasons, and solar cycles is very complicated and remains not well established. Using Total Electron Content (TEC) data from global GNSS receiver networks processed at MIT Haystack Observatory, we perform a detailed statistical analysis of MSTIDs over the Continental US (CONUS). Differential TEC data every day from 2012 to 2023 are processed using a keogram-based image processing technique to identify MSTID wave properties, including the occurrence, propagation direction, phase speed, wavelength, and period. Focusing on eastern US midlatitudes (80°W, 40°N), we extend comparisons longitudinally and latitudinally across CONUS. Our results reveal significant variability in MSTID occurrence rates and propagation directions, notably linked to solar terminators. MSTID occurrence peaks after summer sunrise (with minor maxima near winter daytime), around summer sunset, and after summer midnight. Occurrence generally correlates positively with solar activity in summer but can become negative after winter midnight. In winter, MSTIDs propagate southeastward in the morning and rotate clockwise to west-northwestward after midnight; in summer, propagation is more variable. Comparisons across the CONUS highlight strong regional differences. Our findings reflect complex drivers behind MSTIDs, including gravity waves, electrodynamic processes, and solar terminators. Their relative influences vary with local time, season, and location. This long-term analysis provides critical insights into MSTID climatology and forms a basis for in-depth investigations of MSTID generation mechanisms.

Spatial geographic variability in Earth's core magnetic field, measured at 400 km altitude but corrected for ionospheric and magnetospheric signals, correlates with electron flux levels measured by the RBSP spacecraft. A higher Earth's |B| magnitude results in lower flux over L2-6. Over 20 eV–2 MeV, at L2-4, this negative correlation is as large as −0.21, peaking at the 158 keV electrons, with the strongest effects in the 71 keV–2 MeV electrons. Despite higher L shells being well above the 400 km field measure, statistically significant correlation with the core field was still seen in higher energy 1–2 MeV electrons over L5-6. Adding Earth's geographic |B| variability as a covariate in regression or ARMAX analyses, particularly at lower L shells, results in stronger correlations between electron flux and solar wind, substorm, and ULF wave drivers, with possible nonlinearity in the associations accounted for by taking logs of the variables. At L2, substorms (measured by the SME index), ULF waves, and solar wind velocity show increased correlations with electron flux (30%, 100%, and 175%, respectively) when Earth's |B| is added as a covariate to the ARMAX regression models. Modest increases in correlation of electron flux with these possible drivers were also seen at L3-6. This argues for the addition of Earth's |B| as a covariate in models of electron response to drivers.

A number of mechanisms have been suggested to operate within the terrestrial bow shock to redistribute energy contained in the incoming solar wind flow. The majority of mechanisms involve the generation of turbulence while some are based on particle motion alone. In this paper, we investigate the possible occurrence of the Electron Trajectory Instability, that results from short scale electric field gradients. Spike-like bipolar features in electric field measurements are a commonly observed signature within the terrestrial bow shock. They are usually associated with the passage of electrostatic solitary waves associated with phase space holes in the particle distribution. Using electric field measurements, we compare different interferometric methods to determine the propagation direction, velocity, and spatial scale of these features. Based on these results, it appears that the instability criterion for the Electron Trajectory Instability is fulfilled and the electron trajectories will diverge in the presence of these structures.

The zonal neutral wind is generally believed as the driving source of zonal drift of the equatorial plasma bubbles (EPBs). Comparing their correlations is crucial for understanding the zonal drift of EPBs. However, studies on their relationship by utilizing ground-based observational data are very limited, especially in the Chinese sector. In this study, we conducted a statistical comparison between the EPB zonal drift velocity estimated from an All-Sky Airglow Imager (ASAI) and the zonal neutral wind obtained from a Fabry-Perot Interferometer (FPI) and a Dual-Channel Optical Interferometer (DCOI) deployed at the Fuke ($���19.5�°��N�$; $���109.1�°��E�$, dip latitude ∼9.7°N) station over more than 1 yr, from June 2023 to December 2024. The results show that the zonal drift velocities of over 50% EPB events are generally consistent with the zonal neutral wind velocities. For the remaining cases, the EPB zonal drift velocity differs from the zonal neutral wind velocity, with more pronounced deviations observed around midnight. Before midnight, events with EPB zonal drift velocities lower than the wind velocity outnumber those with higher velocities. After midnight, this trend reverses, with higher EPB velocities becoming more frequent. Additionally, the differences between EPB zonal drift velocity and zonal neutral wind velocity exhibit seasonal variations and are modulated by geomagnetic activity. These results provide valuable insights for advancing our understanding of the patterns and physical mechanisms governing EPB zonal drift.

The zonal neutral wind is generally believed as the driving source of zonal drift of the equatorial plasma bubbles (EPBs). Comparing their correlations is crucial for understanding the zonal drift of EPBs. However, studies on their relationship by utilizing ground-based observational data are very limited, especially in the Chinese sector. In this study, we conducted a statistical comparison between the EPB zonal drift velocity estimated from an All-Sky Airglow Imager (ASAI) and the zonal neutral wind obtained from a Fabry-Perot Interferometer (FPI) and a Dual-Channel Optical Interferometer (DCOI) deployed at the Fuke ($���19.5�°��N�$; $���109.1�°��E�$, dip latitude ∼9.7°N) station over more than 1 yr, from June 2023 to December 2024. The results show that the zonal drift velocities of over 50% EPB events are generally consistent with the zonal neutral wind velocities. For the remaining cases, the EPB zonal drift velocity differs from the zonal neutral wind velocity, with more pronounced deviations observed around midnight. Before midnight, events with EPB zonal drift velocities lower than the wind velocity outnumber those with higher velocities. After midnight, this trend reverses, with higher EPB velocities becoming more frequent. Additionally, the differences between EPB zonal drift velocity and zonal neutral wind velocity exhibit seasonal variations and are modulated by geomagnetic activity. These results provide valuable insights for advancing our understanding of the patterns and physical mechanisms governing EPB zonal drift.

Electromagnetic ion cyclotron (EMIC) waves are a key driver of particle precipitation and energy redistribution in the magnetosphere. While they have been extensively studied in the inner magnetosphere, their behavior in the outer magnetosphere remains poorly understood. In this study, we utilize ground-based measurements from the Autonomous Adaptive Low-Power Instrument Platform (AAL-PIP) chain to investigate the occurrence and amplitude of H-band and He-band EMIC waves under varying AE, SYM-H, and solar wind dynamic pressure ($��P_d�$) in Earth's outer magnetosphere (L > 7). In the outer magnetosphere, both the occurrence rate and amplitude of EMIC waves increase under high AE and enhanced $��P_d�$ conditions, similar to responses in the inner magnetosphere. However, unlike the inner magnetosphere, where EMIC waves are generally confined near noon, enhanced $��P_d�$ in the outer magnetosphere drives waves across a broader magnetic local time (MLT) distribution, including the dawn and dusk sectors. Furthermore, during substorm periods, H-band EMIC waves are absent in the dawn sector—a feature rarely observed in the inner region. SYM-H shows only a weak correlation with wave amplitude and He-band wave occurrence, while a stronger correlation is found with H-band wave activity in both dawn and dusk sectors. Additionally, the radial dependencies also differ: as L increases, the wave occurrence rate decreases for both bands, but H-band amplitudes increase while He-band amplitudes decrease. This likely reflects differences in ion composition and wave growth conditions at larger radial distances. This study provides new insights into the global distribution and driving physics of EMIC wave activity in the outer magnetosphere.

Electromagnetic ion cyclotron (EMIC) waves are a key driver of particle precipitation and energy redistribution in the magnetosphere. While they have been extensively studied in the inner magnetosphere, their behavior in the outer magnetosphere remains poorly understood. In this study, we utilize ground-based measurements from the Autonomous Adaptive Low-Power Instrument Platform (AAL-PIP) chain to investigate the occurrence and amplitude of H-band and He-band EMIC waves under varying AE, SYM-H, and solar wind dynamic pressure ($��P_d�$) in Earth's outer magnetosphere (L > 7). In the outer magnetosphere, both the occurrence rate and amplitude of EMIC waves increase under high AE and enhanced $��P_d�$ conditions, similar to responses in the inner magnetosphere. However, unlike the inner magnetosphere, where EMIC waves are generally confined near noon, enhanced $��P_d�$ in the outer magnetosphere drives waves across a broader magnetic local time (MLT) distribution, including the dawn and dusk sectors. Furthermore, during substorm periods, H-band EMIC waves are absent in the dawn sector—a feature rarely observed in the inner region. SYM-H shows only a weak correlation with wave amplitude and He-band wave occurrence, while a stronger correlation is found with H-band wave activity in both dawn and dusk sectors. Additionally, the radial dependencies also differ: as L increases, the wave occurrence rate decreases for both bands, but H-band amplitudes increase while He-band amplitudes decrease. This likely reflects differences in ion composition and wave growth conditions at larger radial distances. This study provides new insights into the global distribution and driving physics of EMIC wave activity in the outer magnetosphere.

A moderate geomagnetic storm was driven by high-speed solar wind stream on 14 March 2016. We show that large-scale traveling ionospheric disturbances (LSTIDs) played a significant role in producing the ionospheric storm positive phase at mid-latitudes in the North American sector. The equatorward expansion of the positive storm phase followed the equatorward propagation of the LSTIDs, after which the total electron content (TEC) increased by 11 TECU (42%). Our novel method to estimate Joule heating suggests that sudden increases in Joule heating in the auroral oval triggered the LSTIDs. The effects of the LSTIDs observed by the Millstone Hill radar were sudden uplifts of the ionospheric F region followed by downlifts. The absence of an eastward electric field in the radar measurements rules out the role of electric field in causing the positive storm phase. We suggest that the uplifts of the ionosphere were associated with equatorward neutral wind perturbations carried along with the LSTIDs, whereas the downlifts were associated with poleward winds. During the whole period of the two LSTIDs, the TEC continued to increase. The increase in TEC during the uplift can be explained by the decrease in the recombination rate at higher altitudes under continuous solar photoionization. The maximum in peak-F density during the second downlift can be explained by compression of the plasma. To explain the increase in TEC during the downlift, an additional mechanism is needed, which could be downward plasma flux from the plasmasphere or increase in atomic oxygen due to changes in thermospheric circulation.

A moderate geomagnetic storm was driven by high-speed solar wind stream on 14 March 2016. We show that large-scale traveling ionospheric disturbances (LSTIDs) played a significant role in producing the ionospheric storm positive phase at mid-latitudes in the North American sector. The equatorward expansion of the positive storm phase followed the equatorward propagation of the LSTIDs, after which the total electron content (TEC) increased by 11 TECU (42%). Our novel method to estimate Joule heating suggests that sudden increases in Joule heating in the auroral oval triggered the LSTIDs. The effects of the LSTIDs observed by the Millstone Hill radar were sudden uplifts of the ionospheric F region followed by downlifts. The absence of an eastward electric field in the radar measurements rules out the role of electric field in causing the positive storm phase. We suggest that the uplifts of the ionosphere were associated with equatorward neutral wind perturbations carried along with the LSTIDs, whereas the downlifts were associated with poleward winds. During the whole period of the two LSTIDs, the TEC continued to increase. The increase in TEC during the uplift can be explained by the decrease in the recombination rate at higher altitudes under continuous solar photoionization. The maximum in peak-F density during the second downlift can be explained by compression of the plasma. To explain the increase in TEC during the downlift, an additional mechanism is needed, which could be downward plasma flux from the plasmasphere or increase in atomic oxygen due to changes in thermospheric circulation.