Journal of Geophysical Research: Space Physics最新文献

Though the Moon does not possess a global magnetic field like the Earth, there are localized crustal magnetic fields on the lunar surface. Because of the plasma interaction with the crustal magnetic fields, electrostatic and electromagnetic environments near magnetized regions can differ from those near non-magnetized regions on the Moon. Previous studies observationally revealed the difference in the electrostatic potential on the lunar surface between magnetized and non-magnetized regions of the Moon in the solar wind, which was attributed to upward electric fields formed by electron-ion decoupling above the magnetic anomaly regions. However, these inhomogeneous distributions of surface potentials associated with lunar crustal magnetic fields remain uncharacterized in plasma regimes different from the solar wind. In this study, we use a large number of observations by Kaguya and a numerical model of photoelectrons emitted from the sunlit lunar surface to investigate the horizontal distributions of the lunar surface potential in the terrestrial magnetotail lobes. We estimate the relative surface potential variations from the measured energy shift of lunar surface photoelectrons. The results indicate that photoelectrons emitted from relatively strong crustal magnetic field regions tend to be more decelerated, suggesting more positive potentials on the magnetized surface. This implies that upward electric fields are formed by the interaction of terrestrial magnetotail plasma with the lunar crustal magnetic fields in a similar manner to the solar wind interaction with lunar crustal magnetic fields.

Enhanced plasma lines (PLs) obtained from incoherent scatter radars can be utilized to estimate multiple parameters of the ionosphere. The occurrence rates of these PLs, intensified by auroral precipitations, depend on the magnetic local time (MLT) according to the source regions of the precipitated electrons. To comprehensively understand how both nightside and dayside PLs respond to the solar-wind-magnetosphere-ionosphere coupling interactions, we present the first-ever 11-year statistical analysis of PLs data. This analysis is based on the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radar data set, spanning from 2009 to 2019. Our statistical analysis reveals distinctive characteristics in the behavior of enhanced PLs. The occurrence rates of PL enhancements in the E-region peak during nighttime (19:00–07:00 MLT), aligning with the activity of secondary electrons from the magnetotail, while in the F-region peaks occur during daytime (07:00–19:00 MLT), consistent with electron beams from the cusp. A clear seasonal preference emerges, with higher occurrence rates of PL enhancements in the E-region during winter and in the F-region during summer. This observation may be attributed to heightened auroral activity during equinoctial months. Additionally, the PL enhancements demonstrate a correlation with intervals of heightened solar-geomagnetic activity, providing further evidence for a robust connection to auroral precipitation. These findings offer valuable insights into the excitation mechanisms of enhanced PLs and present a novel tool for advancing research in particle precipitation.

Mirror mode structures are born from a plasma instability driven by a large temperature anisotropy and appear downstream of planetary and interplanetary shocks, in their magnetosheath. As so-called “magnetic bottles” imprisoning dense and hot plasma, they are usually observed downstream of their region of formation, where the anisotropy is large and free energy is available, implying that they are advected with the plasma flow to the detection region. At Earth and other planets, the quasi-perpendicular shock provides the plasma with the necessary heating along the perpendicular direction to the local magnetic field. At Mars, which boasts an extended exosphere, an additional source of temperature anisotropy exists, through unstable ring-beam velocity distributions, that is, through ions locally ionized and subsequently picked up by the local electric fields. We report here for the first time an example of near locally-generated mirror mode structures due to pickup protons at Mars using the full plasma instrument suite on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We present events with mirror modes in quasi-perpendicular and quasi-parallel shock conditions, discuss the locality of their generation and show that, in addition to the classic quasi-perpendicular source of anisotropy, another source exists, that is, unstable pickup protons. The existence at Mars of this extra ion anisotropy-generating mechanism is reminiscent of comets.

Due to the relative location of the Sun, Earth, and Moon, a common and special phenomenon occurs, termed a solar eclipse. During the solar eclipse, the solar radiation is greatly obscured, therefore, a series of disturbances could be imposed into the ionosphere. Using electron density observations from the Challenging Minisatellite Payload satellite, the equatorial electrojet (EEJ) measurements from the ground station, and simulations from the Thermosphere Ionosphere Electrodynamic General Circulation Model, this work explored the behaviors of EEJ during the total solar eclipse on 29 March 2006. The path of this solar eclipse goes across the dip equator, providing an opportunity for us to explore the perturbations of EEJ. It is found that the observed EEJ at the MBO station is reduced, with a maximum and average percentage of 38.85% and 19.43%, respectively. The perturbations of EEJ are not only established that are directly affected by the solar eclipse but also after the solar eclipse ends. Local Cowling conductivity associated with E-region electron density is greatly decreased when the solar eclipse occurs. The zonal electric field established by the E-region wind might play a key role in the regulation of EEJ in both eclipse and post-eclipse phases.

During the Van Allen Probes era, several multi-MeV (>4 MeV) electron flux enhancements were observed. The cause of electron acceleration up to multi-MeV remains an ongoing science topic. In this study, we focus on examining the relationship between phase space density (PSD) radial profile shapes and the occurrence of multi-MeV electron flux enhancement events. This will determine which process (local acceleration or radial diffusion) is dominant in producing multi-MeV electron flux enhancements at a specific L*. Growing peaks in PSD radial profiles are associated with the local acceleration (i.e., a wave-particle interaction) of multi-MeV electrons. For each growing peak in PSD, we determined the L* where the local acceleration occurs for each respective electron energy. Similarly, we also identify which PSD profiles are related to acceleration via radial diffusion profiles. Both sets of profiles are compared with the Van Allen Probe-A observed multi-MeV electron flux enhancements. Results show that both mechanisms (local acceleration and radial diffusion) can facilitate multi-MeV electron acceleration, however each mechanism has a preferable L* region where it is the dominant acceleration process.

Characterizing the spatial and temporal variations of the equatorial ionization anomaly (EIA) is essential for understanding ionospheric dynamical processes and further developing empirical total electron content (TEC) models. Using the multiple-source fused TEC data during the solar minimum period, the EIA crest and trough positions were extracted, analyzed, and modeled. We primarily investigated the longitudinal differences in the probability of bimodal occurrence (PBO) and its time dependence at each longitude. The main results are as follows: (a) The PBO exhibits significant longitudinal variation, with a wave-number-3 structure from 11:00 to 13:00 LT and a wave-number-4 structure around 15:00 LT. There is a sequential enhancement and recession among four sectors from east to west between 09:00 LT and 15:00 LT. (b) The seasonal dependence of PBO varies across sectors, particularly during the solstice months. The wavenumber spectral components of TEC along the longitudinal direction exhibit similar temporal patterns, suggesting that the atmospheric tides may modulate the local time and seasonal dependence of PBO. (c) Two EIA position models were developed. The model based on longitude and month can accurately capture the seasonal and spatial variations in the locations of peaks and troughs, with a mean residual of 0° and a standard deviation of 2.1°–2.3°.

On 15 January 2022, the submarine volcano in Hunga Tonga-Hunga Ha’apai (hereinafter Tonga volcano) erupted at 04:14 universal time. This study investigated the two- and three-dimensional co-volcanic ionospheric disturbances (CVIDs) induced by the strong Tonga volcano. Based on dense Global Navigation Satellite System network data in Australia, the two-dimensional detrended total electron content maps were first generated by using the Savitzky-Golay filtering method. Using a compressed sensing-based computerized ionospheric tomography approach, the three-dimensional ionospheric electron densities were reconstructed. After the eruption, the distinctive CVIDs began to be mostly observed over southeastern Australia, about 4,000 km from the volcano. Two patterns of observable CVIDs, that is, fast-mode and slow-mode CVIDs, traveled outward from the Tonga volcano at speeds of 600–850 and 200–350 m/s, respectively. The slow-mode CVIDs were related to the Lamb and secondary gravity waves, while the fast-mode CVIDs were related to acoustic waves. Three-dimensional reconstruction results demonstrated that as the CVIDs propagated upward, the electron densities fluctuated at most altitude-longitude slices, and the wave-like propagating patterns were clearly observed around the peak ionospheric heights of 260–340 km. At the peak ionospheric height, the ionospheric parameters derived from the two ionosondes over Australia also detected similar wave-like features. Two-dimensional and three-dimensional observational evidence of the Tonga-induced CVIDs enhances research on volcanic eruption effects over the upper ionosphere.

An earthquake doublet occurred in Turkey on 6 February 2023, with propagating Rayleigh waves triggering perturbations in the ionospheric total electron content (TEC) for both the M 7.8 earthquake (EQ7.8) and the M 7.5 earthquake (EQ7.5). A discrepancy between the velocities of TEC perturbations and Rayleigh waves has been noted, but its causes remain unresolved in previous studies. In this study, we calculated the velocities of TEC perturbations and the frequency-dependent velocities of Rayleigh waves, considering their intrinsic dispersive characteristics. To retrieve TEC, we utilized ground-based Global Navigation Satellite System (GNSS) data from geostationary Earth orbit (GEO) satellites to mitigate the effects of moving ionospheric pierce points (IPPs) from orbiting satellites. The results reveal that the velocities of TEC perturbations ($��\sim �$2.60 km/s for EQ7.8 and $��\sim �$2.77 km/s for EQ7.5) do not align with the velocities of Rayleigh waves across the entire frequency band (2.4–3.0 km/s for EQ7.8 and 2.6–3.5 km/s for EQ7.5). However, they are comparable within specific periods of 10–30 s due to dispersion effects for both EQ7.8 and EQ7.5. The dispersive Rayleigh waves, which exhibit significant amplification in the 10–30 s period range, are identified as the primary source of the pronounced coseismic TEC perturbations, particularly for EQ7.5.

High-latitude ionospheric convection is a useful diagnostic of solar wind-magnetosphere interactions and nightside activity in the magnetotail. For decades, the high-latitude convection pattern has been mapped using the Super Dual Auroral Radar Network (SuperDARN), a distribution of ground-based radars which are capable of measuring line-of-sight (l-o-s) ionospheric flows. From the l-o-s measurements an estimate of the global convection can be obtained. As the SuperDARN coverage is not truly global, it is necessary to constrain the maps when the map fitting is performed. The lower latitude boundary of the convection, known as the Heppner-Maynard boundary (HMB), provides one such constraint. In the standard SuperDARN fitting, the HMB location is determined directly from the data, but data gaps can make this challenging. In this study we evaluate if the HMB placement can be improved using data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), in particular for active time periods when the HMB moves to latitudes below $��55�°�$. We find that the boundary as defined by SuperDARN and AMPERE are not always co-located. SuperDARN performs better when the AMPERE currents are very weak (e.g., during non-active times) and AMPERE can provide a boundary when there is no SuperDARN scatter. Using three geomagnetic storm events, we show that there is agreement between the SuperDARN and AMPERE boundaries but the SuperDARN-derived convection boundary mostly lies $��\sim �3�°�$ equatorward of the AMPERE-derived boundary. We find that disagreements primarily arise due to geometrical factors and a time lag in expansions and contractions of the patterns.