JGR:Space physics

The heliosphere is full of galactic cosmic rays (GCR), high-energy charged particles coming isotropically from the galaxy. The GCR interact with the solar wind blown by the Sun carrying out plasma, magnetic fields and transient structures such as interplanetary coronal mass ejections (ICMEs) and their associated magnetic flux ropes (MFR). The GCR interaction with ICMEs has been extensively studied particularly the GCR flux attenuation (known as Forbush decreases) as a result of interacting with the ICME sheath and magnetic field. In this work, we investigate the opposite effect: the MFR's ability to generate GCR anisotropies which an observer may detect as an increase in the GCR flux. To achieve this, we simulated a flux of protons with energies in the 10–160 GeV range arriving from all directions to a cylindrical MFR (with and without sheath) with plasma, magnetic field, and spatial dimensions found in average ICMEs observed at 1 au. By following the individual trajectories of the injected particles we found that the MFR deviates the charged particles preferentially in one direction parallel to the MFR–axis. We also found that the peak of this anisotropic GCR flux depends on: the angle between the MFR and ambient magnetic fields; the presence or not of the sheath region; the energy of the incident particles and the observer location inside the MFR.

The migrating diurnal tide (DW1) is derived by fitting Hough Mode Extensions to the TIMED/TIDI near-global wind measurements within the mesosphere and lower thermosphere between 85 and 100 km from 2004 to 2014. The tidal amplitude peaks around the equinoxes with a large interannual variability of up to 50%. The correlation coefficients between the tidal amplitude variability and the solar cycle as represented by F10.7, stratospheric Quasi-Biennial Oscillation (QBO), and El Niño-Southern Oscillation (ENSO) are calculated every 10 days revealing seasonal dependencies. The interannual variability is positively correlated with QBO from spring to fall, maximizing around the equinoxes; anti-correlated to the solar cycle in early winter; and anti-correlated to ENSO in early winter and slightly in March. Multivariate linear regressions are performed to quantitatively analyze the linear relationships between the DW1 amplitude and those factors. The fittings perform best with the QBO at 30 and 50 hPa both being considered. The contribution of QBO peaks around January and October may be related to the polar vortex modulated by QBO in the northern and southern hemispheres, respectively. The correlation between the DW1 amplitude and ENSO is negative with time lags <∼5 months during early winter and spring.

The impact of upstream conditions on magnetopause reconnection has been an intriguing question in solar wind-magnetosphere coupling. In this study, we conduct a statistical analysis of plasma properties in the reconnection outflow region and the associated upstream solar wind/magnetosheath. We observe that the normalized ion density (N/N sw ) decreases and the flow speed (V/V sw ) increases in the upstream magnetosheath with distance from the subsolar point, consistent with previous models and observations. The magnetic field strength (|B|), ion density (N), and ion bulk speed (|V|) in the upstream magnetosheath exhibit close correlations with those in the reconnection outflow region. This upstream-downstream correlation likely arises from the process of forming reconnection outflows, where most upstream ions cross the separatrix and mix with ion outflow already accelerated near the X-line. High-speed part of reconnection outflow is mostly located on the magnetosphere side of the magnetopause current layer, with outflow velocities peaking close to the upstream magnetosheath Alfvén speed. The spatial extent of high-speed outflow is greater in conditions of lower solar wind Alfvén Mach number (M A,sw ). Additionally, the southward magnetic field in the magnetosheath and |B| of magnetopause current layer are larger in the cases of lower M A,sw . These findings indicate a close connection of plasma properties between the outflow region of magnetopause reconnection and the upstream magnetosheath.

We investigate the unique magnetosphere of Uranus and its interaction with the solar wind. Following the work of Masters (2014), https://doi.org/10.1002/2014ja020077 and others, we developed and validated a simple yet valuable and illustrative model of Uranus' offset, tilted, and rapidly-spinning magnetic field and magnetopause (nominal and fit to the Voyager-2 inbound crossing point) in three-dimensional space. With this model, we investigated details of the seasonal and interplanetary magnetic field (IMF) orientation dependencies of dayside and flank reconnection along the Uranian magnetopause. We found that anti-parallel (magnetic field shear angle greater than 170°) reconnection occurs nearly continuously along the Uranian dayside and/or flank magnetopause under all seasons of the 84 (Earth) year Uranian orbit and the most likely IMF orientations. Such active and continuous driving of the Uranian magnetosphere should result in constant loading and unloading of the Uranian magnetotail, which may be further complicated and destabilized by sudden changes in the IMF orientation and solar wind conditions plus the reconfigurations from the rotation of Uranus itself. We demonstrate that unlike the other magnetospheric systems that are Dungey-cycle driven (i.e., Mercury and Earth) or rotationally driven (Jupiter and Saturn), global magnetospheric convection of plasma, magnetic flux, and energy flow may occur via three distinct cycles, two of which are unique to Uranus (and possibly also Neptune). Our simple model is also used to map signatures of dayside and flank reconnection down to the Uranian ionosphere, as a function of planetary latitude and longitude. Such mapping demonstrates that “spot-like” auroral features should be very common on the Uranian dayside, consistent with observations from Hubble Space Telescope. We further detail how the combination of Uranus' rapid rotation and unique and very active global magnetospheric convection should be consistent with fueling of the surprisingly intense trapped radiation environment observed by Voyager-2 during its single flyby. Summarizing, Uranus is a very interesting magnetosphere that offers new insights on the nature, complexity, and diversity of planetary magnetospheric systems and the acceleration of particles in space plasmas, which might have important analogs to exoplanetary magnetospheric systems. Our hypotheses can be tested with further work involving more advanced models, new auroral observations, and unprecedented missions to explore the in situ environment from orbit around Uranus, which should include a complement of magnetospheric instruments in the payload.

This paper introduces a Triangle Network-Joint Slope (TN-JS) approach to characterize the spatial and temporal dynamics of Equatorial Plasma Bubbles (EPBs) during geomagnetic storms. To collaboratively determine the EPB drift directions from multiple stations, a Delaunay triangle network is constructed, utilizing the distribution of Ionospheric Piercing Points (IPPs). The Time Difference of Arrival (TDOA) is extracted through cross-correlating the Rate of Total Electron Content (ROT). The EPB drift direction can be approximately calculated by considering TDOA and IPP distances within each individual triangle of the network. This calculation is then refined through a joint statistical analysis. Using a reference station as the origin, the remaining stations within the network are projected along the estimated EPB drift direction. A spatial-temporal color map illustrating regional ionospheric anomaly ROT observations is constructed. The EPB drift velocity among multiple stations can be collectively estimated by fitting the slope of this map, facilitating outlier exclusion. Accounting for satellite dynamic effects and the diverse orbit characteristics of GPS and BDS, corresponding IPP scan velocity compensation is performed and analyzed for EPB dynamic estimation. Using the geomagnetic storm event that occurred on September 8 as a case study, the spatial-temporal kinetic properties of EPBs is characterized by analyzing Global Navigation Satellite System (GNSS) observations from 17 Hong Kong monitoring stations with the proposed TN-JS approach. The results indicate during this magnetic event, that EPBs exhibit a westward drift trend with velocities ranging from a few tens to hundreds of meters per second in GPS and BDS observations.

Cusp auroras poleward of the typical auroral oval are ascribed to high-latitude lobe reconnection when the Interplanetary Magnetic Field (IMF) B z is predominantly northward. In this study, we further investigate the ionospheric characteristics of a unique high-latitude cusp region employing multiple satellite observations. A cusp aurora event with wide spatial spread was observed in the postnoon polar cap region. It was found to be associated with northward IMF B z and positive B y components. The cusp aurora was located from 68° to 86° in magnetic latitude and within 15–17 hr in magnetic local time. This broad coverage in the polar cap indicates direct precipitating particles from the magnetosheath. Particle energy is different between the equatorward and poleward edges of the cusp aurora. The precipitating ions at the equatorward side maintain magnetosheath particle characteristics as expected, while ions with higher energies occurred in the poleward side. Further, the poleward edge of the cusp aurora was nearly situated in the center of a convection shear and was associated with an upward field-aligned current. These observations suggest a lobe cell circulation, hence we attribute the formation of the cusp aurora to the high-latitude lobe reconnection. Simultaneous observations in the southern hemisphere indicate the absence of cusp aurora. The auroral presence only in the northern hemisphere is probably due to the combination of large dipole tilt angle and positive IMF B z , which facilitates the lobe reconnection.

The solar wind-magnetosphere-ionosphere interaction at Jupiter is reproduced numerically adopting the nine-component magnetohydrodynamic simulation. Calculations take into account the magnetosphere-ionosphere coupling, Jovian rotation, and Io plasma source. High-speed rotating plasma inside restricted magnetospheric space causes expansion and contraction of magnetic field, forming super-rotation at radial distance 20∼30 Rj and co-rotation breakdown further outside. Field-perpendicular current that restores co-rotational delay beyond 30 Rj is connected via field-aligned current to the main oval in the ionosphere. Inside 20 Rj, there is almost co-rotation region (deviation from co-rotation less than 20 km/s). Particularly within 10 Rj, the deviation from co-rotation is less than 2 km/s. In the nearly co-rotating region, the Io plasma forms a disk structure through field-aligned redistribution. The interchange instability occurs near the outer wall of the Io plasma disk, and instability flow develops to vortex. Through this instability, a part of the centrifugal drift current supporting the Io plasma disk is connected to low-latitude field-aligned current that generates beads-like spots on the lower latitude side of the main oval. Resulting interchange instability comes to satisfy the structure of convection and enables further development of vortex. The Coriolis force acting on eastward flow inside the developing vortex makes this flow protrude further outward, forming eastward bending fingers. Inside 10 Rj, Io plasma transport by the interchange instability becomes slower, despite the center of the disk. Io plasma escapes from the inner magnetosphere with a time constant of 20 days if this slow transport is taken into account.

Power line harmonic radiation (PLHR) events are radiated by electric power systems on the ground at harmonics of the base power system frequency (50 or 60 Hz, depending on the region). We analyze the global third harmonics PLHR at 150 and 180 Hz using electric field data collected by China Seismo-Electromagnetic Satellite during the recent solar minimum between January 2019 and December 2022. The average frequency spectrum over industrialized areas shows that the third harmonic has a high occurrence rate in the U.S. region, as well as in western China and northern India, but is very low in the European region. In particular, in the China region and the U.S. region, more than 11,000 and 24,000 dayside and nightside third harmonic PLHR events have been detected from 2019 to 2022, respectively. Compared to the 150 Hz PLHR occurrence rate detected above the China region, the 180 Hz PLHR occurrence rate above the U.S. region is higher, which reveals a significant regional difference. In addition, both at nighttime and daytime, the PLHR electric field intensities at 180 Hz are higher than that at 60 Hz above the U.S. region, which is also different from the result above the China region.

Statistically ion and electron densities are enhanced above strong crustal magnetic field regions according to measurements made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. Plasma created by ionization of neutrals in the lower ionosphere (where chemistry dominates) flows upward and becomes trapped on closed magnetic field loops. Enhanced ion density in the ionosphere (particularly O2+) is associated with enhanced photochemical escape of atomic oxygen. This paper presents a quasi-1D multi-fluid time-dependent model of the Martian ionosphere for nine ion species. Ionospheric temperatures are adopted but ion densities and velocities (along the field lines) are determined using a numerical solution of the continuity and momentum equations. Diurnal effects are explored by varying photoionization rates. Three crustal field cases are considered: a low altitude closed, a high altitude closed, and a high altitude open field line. Additionally, a case with no crustal field is modeled to provide a comparison between regions with and without crustal fields in the upper Martian ionosphere. Model results show higher ion and electron densities in the crustal field cases than in the purely induced field case. Additionally, we find that densities are generally higher on the closed field lines than on the open field lines, and ion velocities are generally up the field lines, away from the Martian surface. We also find that velocities are larger on the open field line case. We compare modeled density results to MAVEN data and find general agreement. Implications for atmospheric escape, particularly photochemical escape of O, are also discussed.

Electron cyclotron harmonic (ECH) waves are electrostatic emissions with frequencies between the harmonics of the electron gyrofrequencies. Their frequency properties provide clues for understanding their generation and are keys to evaluating their scattering efficiency. Based on Magnetospheric Multiscale satellite observations, we explored the statistical frequency properties of first-harmonic band ECH waves in the outer magnetosphere. The frequencies at the peak power of ECH waves are found to be day-night and dawn-dusk asymmetries, with higher values in the regions from dawn to post-noon, and these asymmetries are more evident during weaker geomagnetic activity. Furthermore, the frequencies at the peak power of ECH waves decrease gradually with increasing |MLAT| and are positively correlated with their amplitudes at each magnetic local time or |MLAT|. Information on the frequency properties of ECH waves presented in this study can be crucial for future modeling of their contributions to magnetospheric electron dynamics.

Detached subauroral proton arcs are commonly observed during the recovery phase of geomagnetic storms, and have been extensively investigated. However, there is limited study on their occurrence during the main phase of storms. This study investigated nightside detached auroras (NDAs) observed by the far-ultraviolet imager onboard the Defense Meteorological Satellite Program spacecraft. The NDAs occurred in the nightside sector, separated from the equatorward boundary of the auroral oval, and were observed during the main and recovery phases of the geomagnetic storm on 02 October 2013. The occurrence of the NDAs appears to correlate with the expanding auroral oval toward lower latitudes, and is independent of the polarity change in the interplanetary magnetic field Bz component. Particle measurements indicate that the NDAs were generated by energetic protons, primarily above 10 keV, originating from the ring current. These precipitating proton fluxes, predominantly anisotropic, were observed to be detached from the isotropic boundary within the auroral oval. Analysis of Pc1 data obtained by ground stations suggests that electromagnetic ion cyclotron waves account for the generation of the NDAs. The limited latitudinal distribution of the NDAs indicates the wave activity in the magnetospheric source region within a narrow L-shell region. The observations presented in this study would contribute to our understanding of the coupling processes between the magnetosphere and ionosphere within the subauroral region.

This study focuses on the poorly known effect of polar cap patches (PCPs) on the ion-neutral coupling in the F-region. The PCPs were identified by total electron content measurements from the Global Navigation Satellite System (GNSS) and the ionospheric parameters from the Defense Meteorological Satellite Program spacecraft. The EISCAT incoherent scatter radars on Svalbard and at Tromsø, Norway observed that PCPs entered the nightside auroral oval from the polar cap and became plasma blobs. The ionospheric convection further transported the plasma blobs to the duskside. Simultaneously, long-lasting strong upper thermospheric winds were detected in the duskside auroral oval by a Fabry-Perot Interferometer (FPI) at Tromsø and in the polar cap by the Gravity Recovery and Climate Experiment satellite. Using EISCAT ion velocities and plasma parameters as well as FPI winds, the ion drag acting on neutrals and the time constant for the ion drag could be estimated. Due to the arrival of PCPs/blobs and the accompanied increase in the F-region electron densities, the ion drag is enhanced between about 220 and 500 km altitudes. At the F peak altitudes near 300 km, the median ion drag acceleration affecting neutrals more than doubled and the associated median e-folding time decreased from 4.4 to 2 hr. The strong neutral wind was found to be driven primarily by the ion drag force due to large-scale ionospheric convection. Our results provide a new insight into ionosphere-thermosphere coupling in the presence of PCPs/blobs.

No abstract is available for this article.

This study uses Mars Atmosphere and Volatile EvolutioN observations of electron density and magnetic field for a period of four Martian years (MYs 33–36) (∼8 Earth years) to investigate the effects of Martian crustal magnetic fields on the distribution and variability of Mars' ionosphere. The results show a clear enhancement in electron density in the southern hemisphere in the region where the strong crustal magnetic fields are present with the longitudes between 120° and 240° (i.e., the central longitude), which is in agreement with previous studies. On the contrary, the corresponding northern hemisphere region in the central longitudes shows an exactly opposite behavior that the electron density is lower compared to the surrounding longitude regions. These effects are found to be primarily dayside phenomena. As opposed to dayside, the nightside electron density in the central longitudes are slightly reduced at altitudes below 200 km, compared to longitudes on its western and eastern sides. Above 200 km, the nightside effects are not very clear. Significant hemispheric asymmetry is observed in the longitude regions of enhanced crustal magnetic fields compared to other longitude regions during the daytime. This dayside south-north asymmetry in the central longitude region is observed to be a constant feature across all seasons. However, on the nightside, the south-north asymmetry remains more or less similar across all longitude regions, during all seasons implying a weakened control of the crustal fields over the nightside ionosphere. Even then, the southern hemisphere retains a stronger nightside ionosphere during all seasons except summer.

Two solar eclipse events in 2023 appeared to produce considerable enhancements in the thermospheric column density ratio of monatomic oxygen to molecular nitrogen (ΣO/N2) as measured by TIMED GUVI. We quantify potential sources for eclipse-induced ΣO/N2 changes and find that the observed enhancements arise from the ionospheric O+ radiative recombination contribution to the OI 135.6 nm emission from which ΣO/N2 is derived. Variations in the solar Extreme Ultra Violet (EUV) and X-ray spectrum, due to the difference between the disk spectrum and the coronal spectrum, are also considered but shown to have negligible contributions to the ΣO/N2 enhancements. After accounting for the radiative recombination contribution, we constrain the real thermospheric compositional change to the uncertainty level of the measurements of 5%–10%. These results are valuable for the interpretation of eclipse-induced ΣO/N2 changes that will further first-principle model comparisons and lead to a better understanding of the response of the thermosphere to localized variations in solar EUV and X-ray forcing.

There are growing concerns about the effect of solar flares on the ionosphere, mainly due to possible deterioration or damage to our communication and navigation satellite systems. On 3 July 2021, and 28 October 2021, there were solar flares (SFs) classified as X1.59 and X1.0, respectively. These two SFs were the only ones of X-class that occurred during the last low solar activity (LSA:2018–2021). Data from magnetometers and Global Positioning System (GPS)—Total Electron Content (TEC) are used to investigate the spatial-temporal electrodynamics of the ionosphere from pole-to-pole in the American sector. Employing ∆H and vertical TEC, along with the ROT (rate of change of VTEC) parameter. Rapidly ∆H disturbances closely follow the X-ray variation and the ∆H valleys and peaks are well-synchronized during the SFs, indicating that they are linked. Major disturbances in the ∆H are noticed in the mid-low-equatorial latitudes. However, minor disturbances were seen at high latitudes. Also, |ROT| is a good indicator of the electron density changes during the SFs, especially when the X-ray intensity rises to the peak.

Radiation Belt Storm Probes (RBSP) data show that seed electrons generated by sub-storm injections play a role in amplifying chorus waves in the magnetosphere. The wave-particle interaction leads to rapid heating and acceleration of electrons from 10's of keV to 10's of MeV energies. In this work, we examined the changes in the radiation belt during geomagnetic storm events by studying the RBSP REPT, solar wind, AL, SML, and Dst data in conjunction with the WINDMI model of the magnetosphere. The field-aligned current output from the model is integrated to generate a proxy E index for various energy bands. These E indices track electron energization from 40 KeV to 20 MeV in the radiation belts. The indices are compared to RBSP data and GOES data. Our proxy indices correspond well to the energization data for electron energy bands between 1.8 and 7.7 MeV. Each E index has a unique empirical loss rate term (τ L ), an empirical time delay term (τ D ), and a gain value, that are fit to the observations. These empirical parameters were adjusted to examine the delay and charging rates associated with different energy bands. We observed that the τ L and τ D values are clustered for each energy band. τ L and τ D consistently increase going from 1.8 to 7.7 MeV in electron energy flux E e and the dropout interval increases with increasing energy level. The average trend of Δτ D /ΔE e was 4.1 hr/MeV and the average trend of Δτ L /ΔE e was 2.82 hr/MeV.

Cross-scale energy transfer is a fundamental problem in plasma physics but is poorly understood. Based on Magnetospheric Multiscale satellite (MMS) data, we present the evidence of the energy transfer between ion-scale and electron-scale waves in the Earth's foreshock region. Low-frequency fast-magnetosonic waves (LFWs, ∼0.2 Hz; ion-gyration scales) are observed in the solar wind upstream of the Earth's bow shock. Due to the magnetic compression of LFWs, suprathermal electrons (∼10–100s eV) are adiabatically heated in the perpendicular direction, which leads to the high anisotropy in the high-magnetic-field region. Then high-frequency whistler mode waves (HFWs, 0.1–0.5 f ce ; electron-gyration scales) are excited by those anisotropic electrons through cyclotron resonance. Therefore, this study reveals how energy is transported from LFWs to HFWs, suggesting that wave-particle interactions have played a key role in cross-scale energy transfer in collisionless plasmas.

The Juno mission flew through the plasma disk near the equator in Jupiter's magnetosphere frequently. We identify 274 plasma disk crossings of Juno between 10 and 40 R J from PJ5 to PJ44. Using a forward modeling method that combines the JADE-I time-of-flight and SPECIES data sets, we perform a survey of ion properties in the plasma disk. Ions are heated from 1.5 to 6 keV between 15 and 30 R J . Density and temperature are locally anti-correlated. Assumed to be related to centrifugal instabilities, cold, dense plasma are commonly observed near midnight. Plasma corotates around Jupiter and the rigid corotation breaks down outside 15–20 R J . The plasma bulk velocity increases from the post-dusk sector to the pre-dawn sector featuring injection flows in the pre-dawn sector, which is consistent with the Vasyliunas cycle. Strong outflows (>100 km/s) are commonly observed outside 20 R J and the average radial velocity increases with radial distance. The ion abundance changes between 10 and 18 R J and that might indicate plasma sources and/or sinks near Europa and Ganymede. The vertical distribution of ions is controlled by the balance between centrifugal, pressure gradient, and ambipolar electric field forces. An example near the M-shell of 13.5 shows that average plasma temperature increases by a factor of 10 from the disk center to edge, because cold ions are more confined near the equator. Lighter ions with higher charge states have more mobility along the field line and have larger scale heights. The observations are compared with multi-species diffusive equilibrium model.

The sporadic E-layer (Es) exhibits unique opportunity for exploring the coupling from lower to upper atmosphere. It was found that the East Asia is with the highest intensity and occurrence probability of Es. By using the long-term data of 21 ionosonde stations in China and Japan over the past 60 yrs, this paper explores the probable control on the Es layer from the lower layers. It is found that the intensity of the Es layer is strongly correlated with the surface atmospheric temperature, terrain, and land-sea boundary. The correlation coefficient of the intensity of Es with surface temperature is as high as 0.8204, while that with the terrain and land-sea boundary is up to 0.6668. Based on the coupling between the lower and upper atmosphere, this paper reveals the probable controls from lower layers on the intensity of the Es in East Asia.