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Charge disproportionation of ferrous iron has been considered as one of the mechanisms for the formation of metallic iron on the lunar surface. However, the detailed mechanism of the disproportionation reaction on the Moon is yet to be elucidated. We provide direct evidence for the ferrous disproportionation reaction that produces nano phase metallic iron (npFe0) during a rapid cooling process after splash melting from a lunar sample returned by China's Chang'e‐5 mission. Space weathering processes have resulted in the formation of three distinct zones at the rim of a pyroxene fragment, as observed through transmission electron microscopy. These zones, made up of splashed melts, newly formed melts from the substrate, and the mineral, are distinguished as I, II, and III. Quantitative analyses of the iron valence state by electron energy loss spectroscopy show that disproportionation reactions occurred in zone II at a low temperature of <570°C during a rapid cooling process. The reaction led to the production of α‐structure npFe0 and Fe3+ reserve in the glass phase. The npFe0 produced by the disproportionation reaction has a larger grain size than those formed from solar wind irradiation, implying that micrometeoroid impacts mainly contribute to the darkening of visible and near‐infrared reflectance. These findings reveal a novel rim structure by repeated space weathering and a universal formation mechanism of npFe0 during micrometeoroid impacts, suggesting that the disproportionation reaction could be widespread on airless bodies with impact‐induced splash processes. [ABSTRACT FROM AUTHOR]

In this work we have studied about the characteristics and dynamical changes during the recovery time of moderate and strong geomagnetic storms of (Dst < − 50 nT ). In our investigation of 57 storms triggered by CMEs/CIRs, we concentrated on the solar wind's influence on their decay phases. Selected storms were classified into distinct groups based on their recovery characteristics. Employing the superposed epoch analysis and best fit methods, we scrutinized several interplanetary solar wind plasma and field parameters and their various functions. The analysis encompassed various single, dual, and multiple interplanetary plasma and field parameters/functions. We determined the most representative characteristic time for the storm's recovery profile by carefully fitting an exponential curve. A correlation analysis between Dst and solar wind parameters/functions led us to isolate a coupling function ( ρ 1 2 Ey ) which best described the decay rate of the ring current. It shows that electric field term (Ey) coupled with a viscus term ( ρ 1 2 ) plays pivotal role in determining the recovery rate of a geomagnetic storms. Additionally, we modeled the complex patterns of Dst recovery in relation to solar wind parameters and functions using a second-order polynomial. Remarkably, during the recovery phase, a dynamic correlation between Dst and solar wind parameters/functions was revealed. The three-parameter solar wind-magnetosphere electrodynamical coupling functions, which combines the viscus term ( ρ 1 2 ) and the electric field-related function ( v 4 3 B ) ( ρ 1 2 v 4 3 B ), significantly impacts the recovery phase of geomagnetic disturbances. Our investigation extended to the relationship between main and recovery phase durations, providing valuable insights into the solar wind's intricate control over the decay of the geomagnetic disturbances. These findings contribute significantly to advancing our comprehension of the complex relationship between solar wind dynamics and the evolution of geomagnetic disturbances. [ABSTRACT FROM AUTHOR]

The Laser Interferometer Space Antenna (LISA) of the European Space Agency will be the first interferometer for low-frequency ( 10 - 4 – 10 - 1 Hz) gravitational wave detection in space. LISA will detect spurious accelerations of the test masses, the end mirrors of the interferometer, of the order of femto-g. Amongst spurious signals, Coulomb forces due to stray electric fields coupling with charge deposited on the test masses by galactic and solar particles and the noise associated to the charging process must be monitored during the mission lifetime. Precious clues on spurious forces acting on the test masses have been studied with the LISA Pathfinder mission, meant for the testing of the instrumentation that will be placed on board LISA, in 2016–2017. In this work we present the design and implementation of a workflow leading to equation discovery for the relationship between solar wind speed, galactic cosmic-ray variations and interplanetary magnetic field intensity observations for the diagnostics of LISA. The workflow exploits explainable artificial intelligence tools to build a bridge between the opaque predictions obtained with machine learning (ML) models and data analysis performed by humans with space mission observations. The core step of the workflow is the implementation, tuning and optimisation of an opaque ML regressor explicitly designed for the future LISA mission, based on input observations of the galactic cosmic-ray flux and of the interplanetary magnetic field intensity. The regressor is aimed at reconstructing the solar wind speed, a parameter of fundamental importance, but not available, for the mission environment monitoring. The workflow ends with the application of explainable clustering techniques to the opaque model in order to (i) obtain human-interpretable outputs instead of opaque ones without any noticeable loss in the predictive performance and (ii) discover an equation describing the quantitative relationship between the involved variables, currently missing in the literature. The correlation amongst the transit of interplanetary structures, galactic cosmic-ray variations and LISA test-mass charging is illustrated here. [ABSTRACT FROM AUTHOR]

Parker Solar Probe, the closest spacecraft to the Sun, has renewed our understanding of the solar corona and the interplanetary space. One of its important findings is the prevalence of switchbacks, which display localized magnetic reversals along the otherwise Parker spirals. While some switchbacks might disappear quickly, others can maintain for a long period of time, and there are indications that many switchbacks strengthen from the solar corona to the interplanetary space despite their magnetic tension force, which tends to straighten the magnetic field lines. Therefore, how these switchbacks could be maintained for a long period of time remains a mystery. In this paper, we employed a 3D data-driven global full magnetohydrodynamics numerical model to explore the evolution of switchbacks formed in the dynamic corona. Our simulations indicate that two factors can affect the lifetime of a switchback. One factor is the combination of angle and leg length ensures that the switchback with greater curvature after reconnection can last longer, and the greater the angle, the more magnetic field lines that can be reconnected, and thus the longer the duration. We call this influencing factor flux tube shape factor. The other factor is the velocity shear, i.e., when the solar wind at the convex-outward turning of a switchback is faster than that at the concave-outward turning, the switchback becomes enhanced during propagation, and it weakens when the velocity difference is opposite. [ABSTRACT FROM AUTHOR]

Whistler-mode waves have been extensively observed and investigated in terrestrial space. In this study, we present the dynamic response of whistler-mode waves to different solar wind conditions in the dayside terrestrial space based on Magnetospheric Multiscale (MMS) data. Statistical results show that the occurrence rate, amplitudes, and corresponding electron temperature anisotropy of whistler-mode waves increase with P sw in the dayside terrestrial space, which is attributed to the compression of magnetic fields in these magnetosheath and outer magnetosphere. Furthermore, whistler-mode waves under the southward interplanetary magnetic fields (IMFs) show a higher occurrence rate than that under the northward IMFs, mostly corresponding to T e ⊥/ T e ∥ > 1, and have a higher occurrence rate during quasi-radial IMFs. These results present that whistler-mode waves in these magnetosheath and outer magnetosphere are also modulated by the solar wind as clearly as the inner magnetosphere. This work advanced our understanding in the solar–terrestrial interaction. [ABSTRACT FROM AUTHOR]

Renewable energy is becoming more attractive as traditional fossil fuels are rapidly depleted and expensive, and their use would release pollutants. Power systems that use both wind and solar energy are more reliable and efficient than those that utilize only one energy. Hybrid renewable energy systems (HRES) are viable for remote areas operating in standalone mode. This paper aims to present the state-of-the-art research on off-grid solar-wind hybrid energy systems over the last two decades. More than 1500 published articles extracted from the Web of Science are analyzed by bibliometric methods and processed by CiteSpace to present the results with figures and tables. Productive countries and highly cited authors are identified, and hot topics with hotspot articles are shown in landscape and timeline views. Emerging trends and new developments related to techno-economic analysis and microgrids, as well as the application of HOMER software, are predicted based on the analysis of citation bursts. Furthermore, the opportunities of hybrid energy systems for sustainable development are discussed, and challenges and possible solutions are proposed. The study of this paper provides researchers with a comprehensive understanding and intuitive representation of standalone solar-wind hybrid energy systems. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) drive space weather effects at Earth and the heliosphere. Predicting their arrival is a major part of space weather forecasting. In 2013, the Community Coordinated Modeling Center started collecting predictions from the community, developing an Arrival Time Scoreboard (ATSB). Riley et al. (2018, https://doi.org/10.1029/2018sw001962) analyzed the first 5 years of the ATSB, finding a bias of a few hours and uncertainty of order 15 hr. These metrics have been routinely quoted since 2018, but have not been updated despite continued predictions. We revise analysis of the ATSB using a sample 3.5 times the size of that in the original study. We find generally the same overall metrics, a bias of −2.5 hr, mean absolute error of 13.2 hr, and standard deviation of 17.4 hr, with only a slight improvement comparing between the previously‐used and new sets. The most well‐established, frequently‐submitted model results tend to outperform those from seldomly‐contributed models. These "best" models show a slight improvement over the 11 year span, with more scatter between the models during early times and a convergence toward the same error metrics in recent years. We find little evidence of any correlations between the arrival time errors and any other properties. The one noticeable exception is a tendency for late predictions for short transit times and vice versa. We propose that any model‐driven systematic errors may be washed out by the uncertainties in CME reconstructions in characterization of the background solar wind, and suggest that improving these may be the key to better predictions. Plain Language Summary: Coronal mass ejections (CMEs) are huge explosions that erupt from the Sun and travel through the solar system. It is important to have warning of when they reach Earth, so many researchers model the arrival time (AT) of CMEs. Many predictions are collected in the AT Scoreboard (ATSB), and the general errors from the first 5 years of the ATSB were determined in 2018. These errors are very important as a measure of the uncertainty of predictions, but they have not been updated in over 6 years. Now the data set is over 3.5 times larger so we determine updated results but ultimately only see a small change in the errors. We find a bias of only a few hours, so no strong tendency for either early or late predictions. We find an average absolute error of 13.2 hr but a wide range about this value for individual cases. We do see some evidence that the most commonly used models have improved over time, but the change is very small and there are many factors affecting whether it is significant or not. We suggest that improving how we reconstruct CME properties and model the background solar wind may improve predictions. Key Points: From 1702 arrival time predictions we find a bias of −2.5 hr, mean absolute error of 13.2 hr, and standard deviation of 17.4 hrThe routinely‐submitted models all perform fairly similar but there is more variation in models with smaller data setsWe find evidence of late predictions for coronal mass ejections (CMEs) with short transit times, and early predictions for CMEs with long transit times [ABSTRACT FROM AUTHOR]

The space weather effects at the Earth's magnetosphere are mostly driven by the solar wind that carries the interplanetary magnetic field (IMF). In this paper, we use 2 years of data in the solar wind from lunar orbiting ARTEMIS and MMS spacecraft upstream of the Earth's bow shock to study the structure of the IMF. We determine the lag times of IMF structures and their dependence on spacecraft positions by conducting an information theory analysis and comparing it with two traditional analysis methods: cross‐correlation (CC) analysis and minimum variance of magnetic field analysis (MVAB). For the events with long time intervals (i.e., >4 hr) and with small‐spatial separation between the MMS and ARTEMIS along the yGSM‐direction (i.e., <40Re, where Re is the Earth's radius), the lag times based on the CC and the mutual information (MI) analyses statistically agree with each other, with p‐values of 1.675 × 10−7 and 4.833 × 10−9, with the confidence of 95%. Both the results based on MI and CC have a large deviation from the results from MVAB. For some of the events, such a deviation could be improved by taking the fast mode speed into account; however, p‐tests showed that they were not statistically significant to the 95% confidence level. Plain Language Summary: Typically, single‐point measurements from the Earth‐Sun Lagrange Point‐1 are used to forecast space weather. However, it is important to understand that multi‐point measurements are required to further understand and predict geo‐effective solar wind structures. Three analysis methods using multi‐point measurements from the MMS and THEMIS missions of large solar wind structures as they move from regions around the Moon to regions around Earth's bow shock, are presented and compared in this paper. Information theory analysis (specifically Mutual Information) determines dependence between two variables by quantifying the entropy (uncertainty) in the two variables. Minimum variance analysis calculates the direction of least change in a magnetic field and assumes the solar wind is propagating in that direction. Lag time is calculated by taking the dot products of this direction with both the displacement vector between the two spacecraft, to get a distance, and the ion velocity (from ARTEMIS) to get a speed. The distance is divided by the speed to get a lag time. Cross‐Correlation analysis is a traditional method for measuring similarity between two variables. This paper shows that information theory analysis along with cross‐correlation analysis could be used successfully for space weather forecasting. Key Points: The solar wind data by MMS and THEMIS are analyzed by using information theory to understand the propagation of solar wind structuresMutual information, linear cross‐correlation, and minimum variance analyses sometimes give different lag‐timesInformation theory analysis along with the traditional method of cross‐correlation analysis could be used successfully for space weather forecasting [ABSTRACT FROM AUTHOR]

Starting from 29 January 2022, a series of solar eruptions triggered a moderate geomagnetic storm on 3 February 2022, followed subsequently by another. Despite the typically minimal impact of unintense storms on space technology, 38 out of the 49 Starlink satellites underwent orbital decay, re‐entering Earth's atmosphere. These satellite losses were attributed to enhanced atmospheric drag conditions. This study employs numerical simulations, utilizing our test particle simulation code, to investigate the dynamics of the inner radiation belt during the two magnetic storms. Our analysis reveals an increase in proton density and fluxes during the transition from the recovery phase of the first storm to the initial phase of the second, primarily driven by intense solar wind dynamic pressure. Additionally, we assess Single Event Upset (SEU) rates, which exhibit a 50% increase in comparison to initial quiet conditions. Plain Language Summary: Starting from 29 January 2022, a series of solar explosions disrupted Earth's magnetic field, resulting in two geomagnetic storms. While such storms typically don't impact space technology significantly, 38 out of the 49 launched Starlink satellites encountered problems, ultimately falling back to Earth and burning up upon reentry due to increased atmospheric drag. In our study, we examined the inner radiation belt during these two consecutive magnetic storms. Using a simulation code, we conducted a thorough analysis of the inner proton belt's behavior in February 2022. Notably, we observed a rise in proton density within the inner belt from the end of the first magnetic storm to the beginning of the subsequent storm. Additionally, we assessed the resulting Single Event Upset rates, which increased by 50% compared to the initial quiet conditions. Key Points: We simulated the inner proton belt's activity during the two successive geomagnetic storms of February 2022The proton flux in the South Atlantic Anomaly increased between the first storm's recovery phase and the second storm's initial phaseWe assessed the resulting Single Event Upset rates, which rose by 50% compared to the initial quiet conditions [ABSTRACT FROM AUTHOR]

The Electric Solar Wind Sail (E-sail) is a propellantless propulsion system that converts solar wind dynamic pressure into a deep-space thrust through a grid of long conducting tethers. The first flight test, needed to experience the true potential of the E-sail concept, is likely to be carried out using a single spinning cable deployed from a small satellite, such as a CubeSat. This specific configuration poses severe limitations to both the performance and the maneuverability of the spacecraft used to analyze the actual in situ thruster capabilities. In fact, the direction of the spin axis in a single-tether configuration can be considered fixed in an inertial reference frame, so that the classic sail pitch angle is no longer a control variable during the interplanetary flight. This paper aims to determine the polar form of the propelled trajectory and the characteristics of the osculating orbit of a spacecraft propelled by a low-performance spinning E-sail with an inertially fixed axis of rotation. Assuming that the spacecraft starts the trajectory from a parking orbit that coincides with the Earth's heliocentric orbit and that its spin axis belongs to the plane of the ecliptic, a procedure is illustrated to solve the problem accurately with a set of simple analytical relations. [ABSTRACT FROM AUTHOR]

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 fce; 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. Plain Language Summary: Cross‐scale energy transfer is a fundamental problem in plasma physics, in which wave‐particle interaction plays an important role. Previous studies provide a limited and incomplete picture of the coupling process between high‐frequency whistler mode waves (HFWs, electron‐scale) and low‐frequency fast‐magnetosonic waves (LFWs, ion‐scale), and therefore further investigation is still needed to clarify their coupling mechanism. Based on MMS satellite data, we present a promising coupling process between HFWs and LFWs in the Earth's foreshock region. Observation results indicate that suprathermal electrons are perpendicularly heated by the LFWs in the high‐magnetic‐field region via betatron acceleration. These electrons could generate the HFWs through cyclotron resonance, which is confirmed by both observations and theoretical calculations. Therefore, this event shows the energy transfer among LFWs, suprathermal electrons, and HFWs, illustrating that the energy is directly transported from the ion scale to the electron scale. Our finding provides a potential generation mechanism for HFWs, which may be highly important for understanding the electron dynamics in the Earth's foreshock region. Key Points: Using Magnetospheric Multiscale satellite data, we present the evidence of the energy transfer from ion‐scale low‐frequency fast‐magnetosonic waves (LFWs) to electron‐scale high‐frequency whistler mode waves (HFWs) in the Earth's foreshock regionDue to the magnetic compression of the LFWs, suprathermal electrons (∼10–100s eV) are adiabatically heated in the perpendicular directionBoth theoretical analysis and observations suggest that the HFWs are excited by those suprathermal electrons through cyclotron resonance [ABSTRACT FROM AUTHOR]

The present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (fci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of fci. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left‐hand (LH), and higher frequency harmonics are associated with the right‐hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi‐perpendicular directions to the ambient magnetic field. The results of linear theory and Particle‐In‐Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars. Plain Language Summary: Mars is an unmagnetized planet. The solar wind particles that bombard Mars continuously, are responsible for the loss of its atmosphere. This scenario is opposite to that of the Earth, as its strong intrinsic magnetic field forms a protective shield around the planet, called the magnetosphere. Various electrostatic/electromagnetic waves are often generated in the Earth's magnetosphere, which are potential candidates for controlling the transfer of energy and momentum from one region to another. In case of Mars, it possesses a weakly induced magnetosphere, which is dynamic due to its continuous interactions with solar wind. The field measurements from the MAVEN spacecraft can be used to understand plasma waves in the vicinity of Mars. Here, we report the first observations of the harmonics of magnetosonic wave in the Martian magnetosheath region. The magnetosonic waves are low‐frequency compressive waves driven by the ions in the presence of magnetic field. These waves are known to play a role in the particle heating process in the Earth's magnetosphere. Therefore, its observation in the Martian plasma environment is of interest to the scientific community to understand their role in plasma heating in the Martian ionosphere‐magnetosphere system. Key Points: Harmonics of Magnetosonic wave are observed in the Martian magnetosphere in dawn sector (5–10 LT)Magnetosonic harmonics dominantly have right‐handed polarizationAmbient proton density and velocity found to vary with fundamental mode frequency of 46 mHz [ABSTRACT FROM AUTHOR]

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 (τL), an empirical time delay term (τD), 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 τL and τD values are clustered for each energy band. τL and τD consistently increase going from 1.8 to 7.7 MeV in electron energy flux Ee and the dropout interval increases with increasing energy level. The average trend of ΔτD/ΔEe was 4.1 hr/MeV and the average trend of ΔτL/ΔEe was 2.82 hr/MeV. Key Points: The energization rate τL and the time delay τD between initial dropout and subsequent energization of the electrons consistently increase going from the 1.8–7.7 MeV electron energy bandsThe τL and τD values are clustered together for each energy level despite the different storm intervals and intensitiesThe dropout interval increases with an increase in energy level which was obtained based on sub‐storm onsets predicted within the dropout range [ABSTRACT FROM AUTHOR]

Utilizing the multi‐point observations by Van Allen Probe A, GOES 13 and 15, we analyzed the competing influences of earthward convection and azimuthal drift loss on the pitch angle distributions of energetic electrons during the simultaneous increases in solar wind flow velocity and pressure. The increase in solar wind speed amplifies the dawn‐dusk convection electric field and causes the earthward transport of energetic electrons, and meanwhile the enhancement of solar wind dynamic pressure causes the inward displacement of dayside magnetopause and triggers the azimuthal drift loss of energetic electrons. The earthward convection of low‐energy electrons (<60 keV) is much faster than their azimuthal drift loss at most pitch angles, and the fast earthward convections make the butterfly‐like electron pitch angle distributions formed early become pancake‐like distributions. The 60–530 keV electrons maintain the butterfly‐like pitch angle distributions during the earthward convections, whereas the high‐energy electrons above 530 keV are not transported to the low‐L shells because of fast drift loss in the high‐L source region. The competition between the earthward convection and the azimuthal drift loss finally determines the pitch angle distributions of energetic electrons near the trapping boundary during the increases in solar wind flow speed and pressure. Plain Language Summary: Previous studies mainly focus on the butterfly‐like electron pitch angle distributions caused by magnetopause shadowing (drift loss) during the enhancement of solar wind dynamic pressure. However, it is not clear how the electron pitch angle distributions respond to the simultaneous increases in solar wind flow speed and pressure. Here, we found that the pitch angle distributions of different‐energy electrons display different responses to the simultaneous increases in solar wind flow speed and density/pressure. The different electron pitch angle distributions are due to different competitions between the electron drift loss and earthward convection. These results improve our understanding to the formation mechanisms of different electron pitch angle distributions during the simultaneous increases in solar wind flow speed and pressure. Key Points: Increases in solar wind flow speed and dynamic pressure cause the earthward convection and azimuthal drift loss of energetic electronsThe fast earthward convections of low‐energy electrons (<60 keV) flatten their butterfly‐like pitch angle distributions formed earlyThe energetic electrons above 60 keV maintain butterfly‐like distributions because of the fast azimuthal drift loss in high‐L source region [ABSTRACT FROM AUTHOR]

During periods of increased geomagnetic activity, perturbations within the terrestrial magnetosphere are known to induce currents within conducting materials, at the surface of Earth through rapid changes in the local magnetic field over time (dB/dt). These currents are known as geomagnetically induced currents and have potentially detrimental effects on ground based infrastructure. In this study we undertake case studies of five geomagnetic storms, analyzing a total of 19 days of 1‐s SuperMAG data in order to better understand the magnetic local time (MLT) distribution, size, and occurrence of "spikes" in dB/dt, with 131,447 spikes in dB/dt exceeding 5 nT/s identified during these intervals. These spikes were concentrated in clusters over three MLT sectors: two previously identified pre‐midnight and dawn region hot‐spots, and a third, lower‐density population centered around 12 MLT (noon). The noon spike cluster was observed to be associated with pressure pulse impacts, however, due to incomplete magnetometer station coverage, this population is not observed for all investigated storms. The magnitude of spikes in dB/dt are determined to be greatest within these three "hot‐spot" locations. These spike occurrences were then compared with field‐aligned current (FAC) data, provided by the Active Magnetospheric Planetary Electrodynamic Response Experiment. Spikes are most likely to be co‐located with upward FACs (56%) rather than downward FACs (30%) or no FACs (14%). Plain Language Summary: Intense space weather events can cause disruption to key space and ground‐based infrastructures at Earth. One such disruption is caused by rapid perturbations within the magnetic field, resulting in the induction of currents in conductors on the planet surface. In this study, we investigate the occurrence of these rapid changes in the magnetospheric environment by employing magnetometer data from stations positioned around the globe. By identifying instances where the change in magnetic field is most rapid, we analyze the location of these "spikes," in addition to cross‐referencing satellite magnetometer data in order to compare results with corresponding field‐aligned currents present. Key Points: We study the occurrence of dB/dt > 5 nT/s in 1‐s SuperMAG data, with populations found pre‐midnight, dawn and noonLarge dB/dt is most frequently colocated with upward field‐aligned current (FAC)An increase in spike occurrence is observed during negative values of the interplanetary magnetic field component Bz and large values in solar wind pressure, Psw [ABSTRACT FROM AUTHOR]

Electron density enhancements in the ionospheric D‐region due to the precipitation of high‐energy electrons (>30 keV) have been measured as increases in cosmic radio noise absorption (CNA) using ground‐based riometers. CNA has been studied since the 1960s. However, there have been few studies of the spatiotemporal development of CNA at multi‐point ground stations distributed in longitude at subauroral latitudes, where plasma particles with a wide energy range are intermingled. In this study, we analyzed the longitudinal development of CNA steep increases using simultaneous riometer observations at six stations at subauroral latitudes in Canada, Alaska, Russia, and Iceland over 3 years from 2017 to 2020. The results revealed that the occurrence rate of steep increases in CNA was highest at midnight at 22‐08 magnetic local time (MLT), and lowest near dusk at 17–21 MLT. We also showed statistically that the CNA steep increases expanded eastward on the dawn side and westward on the dusk side. The CNA expansion velocity was slightly faster than the results of previous studies in the auroral zone. Correlation and superposed epoch analyses of CNA with solar wind and geomagnetic parameters revealed that CNA intensity was dependent on the Interplanetary Magnetic Field Bz, Interplanetary Electric Field Ey, SYM‐H index, and SME index. These results indicate that the CNA at subauroral latitudes is closely related to solar wind and geomagnetic activities, and its propagation characteristics correspond to the dynamics of high energy electrons in the inner magnetosphere. Plain Language Summary: The inner magnetosphere close to the Earth contains plasma particles with a wide range of energies. It is important to understand the dynamics of high‐energy electrons in the inner magnetosphere for safe space utilization and space weather forecast. This study focuses on the increase in electron density in the Earth's lower ionosphere caused by high‐energy electrons coming down into the atmosphere, based on measurement of cosmic radio noise absorption (CNA) in the ionosphere. Faint radio noise from external astronomical sources can show such absorption, and is slightly less intense, when the ionosphere is bombarded by such electrons. We studied the development in time and space of CNA at multiple ground stations at subauroral latitudes over 3 years. We found statistically that CNA was most likely to occur at midnight and expanded eastward on the dawn side and westward on the dusk side. We also found some correlation between CNA and solar wind and geomagnetic parameters. These results suggest that CNA is closely related to solar wind and geomagnetic activities and shows us the dynamics of high‐energy electrons in the inner magnetosphere. Key Points: This is the first statistical study of longitudinal development of cosmic noise absorption (CNA) using six riometers at subauroral latitudesThe occurrence rate of steep increases in CNA is high at 22‐08 magnetic local time (MLT) and low at 17–21 MLTCNA at subauroral latitudes is closely related to solar wind and geomagnetic activities [ABSTRACT FROM AUTHOR]

In the present study, the influence of the solar wind dynamic pressure on the plasma and magnetic pressures of the magnetosphere is studied. We use 11‐year Time History of Events and Macroscale Interactions during Substorms (THEMIS) instruments for plasma and magnetic field measurements in the magnetosphere and the OMNI database for solar wind dynamic pressure and IMF data. We focus on the effects of the solar wind dynamic pressure (PSW) and consider only times in which the interplanetary magnetic field (IMF) components are within ±5 nT. We find that the plasma pressure inside the magnetosphere follows the solar wind dynamic pressure and that an increase in PSW also influence the day‐night pressure asymmetry. Our analysis also reveals the existence of ion and electron drifts from midnight toward the dusk and dawn sectors, respectively. We observe a local magnetic pressure minimum located near a plasma pressure maximum at around 11 RE on the nightside. Comparing the effect of PSW on both plasma and magnetic pressures, we observe trends which are consistent with the diamagnetic properties of plasmas. In general, the distribution of plasma pressure within the Earth's magnetosphere is an important criterion for evaluating the magnetostatic equilibrium and electric current system. The outcome of this study should provide additional methodologies for the characterization of key plasma characteristics within the magnetosphere. Plain Language Summary: Magnetospheric activity and space weather are driven by the interaction of the solar wind and the Earth's magnetic field. The solar wind dynamic pressure and interplanetary magnetic field (IMF) are two important factors that affect the behavior of the Earth's magnetosphere. The interaction between these two factors are complex and can have significant effects on our planet. Based on 11‐year plasma and magnetic field measurements, obtained from THEMIS satellites, we investigated the effect of solar wind dynamic pressure on the plasma and magnetic pressures within the Earth magnetosphere. In this study, we show that changes in the plasma pressure within the magnetosphere are linked to variations in the solar wind dynamic pressure. Our findings confirm that the plasma pressure inside the magnetosphere is mainly controlled by the solar wind dynamic pressure, which can be attributed to pressure balance. Overall, the distribution of plasma pressure within the Earth's magnetosphere is a key parameter for evaluating the magnetostatic equilibrium and electric current system. Our results are expected to offer scientists additional methodologies for characterizing main plasma parameters in the magnetosphere. Key Points: Increase in solar wind dynamic pressure leads to increase in plasma and magnetic pressures in the magnetosphereLarger solar wind dynamic pressure make the plasma pressure more symmetric around the EarthObservations reveal a local magnetic pressure minimum located near a plasma pressure maximum around 11RE on the nightside [ABSTRACT FROM AUTHOR]

The Earth's magnetosphere is filled with a collisionless plasma that exhibits non‐Maxwellian particle distributions which are well described by Kappa functions. In contrast to the Maxwellian, the Kappa contains not only density and temperature but also the kappa index that allows us to characterize the energetic tails. In this study, we analyze the response of the ion and electron Kappa distributions, obtained by fitting ion and electron fluxes measured by the five THEMIS satellites, to changes of the solar wind dynamic pressure. It was found that the solar wind dynamic pressure strongly affects the values of the kappa index, and that its impact depends on the magnetic local time (MLT). In particular, there is a significant dawn‐dusk asymmetry for low PSW values which is enhanced in the night side. Further, we observe a narrow partial ring‐shaped structure at different azimuthal extension that divides the plasma into two clearly defined domains. The results obtained reflect the global reconfiguration of the magnetosphere caused by variations of the solar wind dynamic pressure. Kappa distribution parameters and their average values for different ranges of PSW and MLT are provided, which we believe will contribute as realistic inputs to the modeling of the magnetosphere. Plain Language Summary: The Kappa distribution function, which combines the Maxwellian‐type and the power‐law distributions, has been widely used in literature to describe particle populations in space and astrophysical plasmas. In such environments, ions and electrons rarely experience collisions and they are out of thermal equilibrium, which allows us to get insights into the mechanism of energy transfer in these plasmas. The goal is to investigate the roles of non‐thermal particle distributions, and their response to solar wind dynamic pressure in poorly collisional plasma environments such as the Earth magnetosphere. The availability of high cadence Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite data have enabled us to conduct this statistical analysis using THEMIS and OMNI database. Our findings confirm that the ion and electron kappa parameters exhibit distinct behaviors when subjected to the dynamic pressure exerted by the solar wind. Moreover, we find an interesting narrow partial ring shaped structure at different azimuthal extension exhibiting a local minimum for ion kappa parameters, and a local maximum for electron kappa parameters. Key Points: The behavior of Kappa distribution parameters in the Earth magnetosphere in response to the variation of the solar wind dynamic pressure is studiedThe solar wind dynamic pressure strongly influence ion and electron kappa indicesThe core energy (Ec) exhibits a significant dawn‐dusk asymmetry for ions and much weaker for electrons in various range of PSW [ABSTRACT FROM AUTHOR]

The magnetosphere‐ionosphere‐thermosphere system is externally driven by the energy input from the solar wind. A part of the solar wind energy deposited in the magnetosphere during geomagnetically active periods dissipates into the thermosphere. Previous studies have reported temperature perturbations in the lower thermosphere during geomagnetic storms. The present study aims to assess the climatological spatial pattern of the lower thermospheric response to geomagnetic activity at high latitudes based on 21 years of temperature measurements by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite and their comparison with the recently developed half‐hourly geomagnetic activity index Hp30. The temperature response to geomagnetic activity, evaluated at different seasons and altitudes, is better organized in magnetic coordinates than in geographic coordinates. At 110 km, the temperature increases with Hp30 at all magnetic local times, but with a prominent dusk‐dawn asymmetry in the magnitude. That is, the temperature variation per unit Hp30 is larger in the dusk sector than in the dawn sector. At 106 km, the response in the dawn sector is further reduced or even negative. These results provide observational evidence to support earlier theoretical predictions; according to which, both storm‐induced vertical wind and Joule heating contribute to the temperature increase in the dusk sector, while in the dawn sector, the vertical wind acts to cool the air and thus counteracts Joule heating. Key Points: High‐latitude lower thermospheric temperature response to geomagnetic activity depends on magnetic local time and magnetic latitudeAbove 100 km, strong and weak (or even negative) responses occur in the dusk and dawn sectors, respectivelyThe results agree with earlier theoretical predictions, highlighting the importance of storm‐induced vertical wind and Joule heating [ABSTRACT FROM AUTHOR]

Localized dynamic pressure enhancements arising from kinetic processes are frequently observed downstream of the Earth's bow shock. These structures, called jets, modify their plasma surroundings and participate in particle energization. Here, we report the first observations of jet-like structures in a non-planetary shock environment: downstream of interplanetary shocks. We introduce an analysis approach suitable for such conditions and apply it to Wind spacecraft data. We present one event with a Mach number similar to the Earth's bow shock as a benchmark, as well as two low Mach number, low beta shocks: a parameter range that is difficult to access at planets. The jet-like structures we find are tens of ion inertial lengths in size, and some are observed further away from the shock than in a limited magnetosheath. We find that their properties are similar to those of magnetosheath jets: in the frame of the shock these structures are fast, cold, and most have no strong magnetic field variations. All three interplanetary shocks feature foreshock activity, but no strongly compressive waves. We discuss the implications, these findings have for the proposed jet formation mechanisms. [ABSTRACT FROM AUTHOR]

As the interplanetary magnetic field (IMF) carried by the solar wind encounters the martian atmosphere, it tends to pile up and drape around the planet, forming looping magnetic fields and inducing marsward ion flows on the nightside. Previous statistical observations revealed asymmetrical distribution features within this morphology; however, the underlying physical mechanism remains unclear. In this study, utilizing a three‐dimensional multi‐fluid magnetohydrodynamic simulation model, we successfully reproduce the asymmetrical distributions of the looping magnetic fields and corresponding marsward flows on the martian nightside. Analyzing the magnetic forces resulting from the bending of the IMF over the polar area, we find that the asymmetry is guided by the orientation of the solar wind motional electric field (ESW). A higher solar wind velocity leads to enhanced magnetic forces, resulting in more tightly wrapped magnetic fields with an increased efficiency in accelerating flows as they approach closer to Mars. Plain Language Summary: As incident solar wind interacts with Mars, the entrained interplanetary magnetic field drapes and stretches around the planet. The draped fields are orientated in opposite directions on the east and west sides of Mars, resulting in magnetic reconnection, the formation of looping magnetic fields and induced marsward plasma flows on the nightside. Statistical observations suggest an asymmetric distribution of these structures, however, the underlying physical mechanisms for this asymmetry have not been determined due to limited spatial coverage offered by the single spacecraft investigations. In this study, by taking advantage of a Hall‐MHD model, we have successfully reproduced the asymmetrical distributions and elucidated the underlying mechanisms governing these morphologies. Simulation results demonstrate that magnetic forces tend to emerge around the polar region, which are determined by the orientation of the ESW, shifting the plasma flows and magnetic fields in the direction opposite to the motional electric field. A higher solar wind velocity condition will induce amplified magnetic forces, resulting in more tightly wrapped magnetic fields and an increase in the velocity of marsward flows closer to the martian nightside. These findings provide valuable insights into the influence of the ESW and solar wind velocity on the martian induced magnetosphere. Key Points: The asymmetrical distributions of looping magnetic fields and associated marsward flows can be well reproduced by a multi‐fluid magnetohydrodynamic (MHD) modelThe impacts of the motional electric field direction and the solar wind velocity on the asymmetries are investigated, respectivelyMagnetic forces shift the magnetic fields and marsward flows toward the direction opposite to the motional electric field [ABSTRACT FROM AUTHOR]

The collisionless nature of planetary magnetospheres means that electromagnetic forces are fundamental in controlling the flow of energy and momentum through these systems. We use Pioneer Venus Orbiter (PVO) observations to demonstrate that the magnetic pumping process can be active at Venus, in analogy to its recent discovery at Mars. The presented case study demonstrates the framework for how the process can work at Venus, and the results of a statistical analysis show that the ambient plasma conditions support the process being active. Magnetic pumping enables low frequency magnetosonic waves to heat ambient ionospheric electrons and provides a mechanism that couples the solar wind to the Venusian ionosphere. This is the first time the magnetic pumping process has been discussed at Venus. Plain Language Summary: Our Sun emits a stream of particles outward into our solar system, known as the solar wind. When these particles encounter planets and other bodies (such as comets), they either collide with the body (as happens with our Moon) or are deflected around the obstacle, similar to how water in a stream flows around a rock (this happens at most planets, including Earth, Venus and Mars). Understanding the physical forces that control this deflection enable us to understand how the Sun interacts with the planets in our solar system. We use in situ measurements made by the Pioneer Venus Orbiter spacecraft, which orbited the planet Venus, to investigate one specific process, known as "magnetic pumping." This process allows energy from the solar wind to flow into the Venusian atmosphere. We provide a case study demonstrating how this process can operate at Venus, and show that the average conditions in the near Venus space environment can support this process in a more general sense. Key Points: A case study demonstrates how the magnetic pumping process operates at VenusStatistical analysis of the plasma conditions at Venus support the notion that magnetic pumping can operate thereMagnetic pumping provides an avenue for the solar wind to couple to the Venusian ionosphere and heat ionospheric electrons [ABSTRACT FROM AUTHOR]

We use in situ plasma observations made by the Pioneer Venus Orbiter spacecraft to show for the first time that magnetosonic waves can couple the solar wind to the upper ionosphere and deposit energy there. The waves are generated upstream of Venus, are advected into the shock and propagate across the draped magnetic field, through the magnetosheath and into the dayside upper ionosphere. The magnetosonic waves damp in the upper ionosphere in a region where physical collisions are rare, and electromagnetic forces must control this damping. The waves damp when the ionospheric heavy ion density is a few thousand cm−3 and wave‐particle interactions with the dominant O+ ions are postulated as the damping mechanism. Estimates of ion heating rates show that 1%–5% of the O+ ion distribution function could be heated to escape energy in 10–40 s. Plain Language Summary: Our Sun emits a stream of charged particles radially outward into our Solar system, known as the solar wind. When the solar wind encounters obstacles such as planets and comets, a variety of forces may act to divert the flow around the obstacle, much like when flowing water in a stream encounters a rock and is diverted around it. This study uses measurements made by a spacecraft that orbited Venus, known as Pioneer Venus Orbiter, to investigate some of the side effects that can arise when the solar wind flow is diverted around Venus. We show for the first time how a particular pathway allows energy to be deposited from the flowing solar wind into the Venusian atmosphere, and that this energy can be deposited quickly enough to significantly impact the particles in the atmosphere. The characteristics observed in this study at Venus are similar to those at Mars where this process has also been observed, suggesting that the solar wind can interact with the two planets in similar ways in this respect. Key Points: Magnetosonic waves propagate from upstream into the dayside upper ionosphere of VenusMagnetosonic waves are damped by wave‐particle interactions with heavy ionospheric ionsSubsequent ion heating rates could heat 1%–5% of the ion distribution function to escape energy in 10–40 s [ABSTRACT FROM AUTHOR]

We report a citizen science‐motivated study on the cause of an unusually bright red aurora as witnessed from Hokkaido, Japan during a magnetic storm on 1 December 2023. The auroral brightness of 5 kR is unusual for the Dst index peak of only −107 nT. In spite of the moderate storm amplitude, the extremely high solar wind density of >50/cc and dynamic pressure of >25 nPa caused the aurora oval extension to 53 magnetic latitudes (L = 2.8). We discuss that the drift loss of the ring current particles across the small‐size magnetopause is important, and Hokkaido was at the right position to see the direct effect of the large particle injection of the storm‐time substorm. Plain Language Summary: Citizen scientists identified an unusually bright red aurora from Hokkaido, Japan during a not‐so‐unusual magnetic storm on 1 December 2023. The large dynamic pressure, driven by large density of >50/cc, contributed to a small magnetopause and the effects observed at such low latitude. The hypothesis of this study is that the loss of ring current particles across the small‐size magnetopause played an important role. Also, we discuss that Hokkaido was at the right position to see the direct effect of storm‐time substorm. Key Points: Unusually bright red aurora was witnessed by citizen scientists from Hokkaido, Japan on 1 December 2023The magnetic storm amplitude was not unusually large, but the solar wind density was high (50/cc)Dynamic pressure and asymmetric evolution of the ring current are important to understand the cause of red‐aurora magnetic storm events [ABSTRACT FROM AUTHOR]

Modification of the solar wind parameters at the bow shock (BS) and through the magnetosheath (MSH) is essential for the solar wind-magnetosphere interaction chain. The present study uses two approaches to determine the spatial profile of magnetic field strength and plasma parameters and their fluctuations along the Sun-Earth line under different interplanetary magnetic field (IMF) orientations with an emphasis on radial IMF conditions. The first method is based on the superposed epoch analysis of all the complete THEMIS MSH crossings between 2007 and 2010. The second approach uses the distance of the observing spacecraft from the model magnetopause (MP) expressed in units of an MSH thickness for all THEMIS observations. The results of both these analyses are consistent, and their comparison with simulations reveals the following features: 1) the sign of the IMF north-south component has a negligible effect on the spatial profile of the magnetic field strength or plasma parameters as well as on the level of fluctuations; 2) the ion temperature is enhanced for a radial MF and it is nearly isotropic throughout MSH; 3) the fluctuation level of plasma parameters just downstream BS is enhanced under a radial IMF, but it gradually decreases toward MP to a value typical for other IMF orientations; 4) magnetic field fluctuations are enhanced by a factor of 1.7 in the whole magnetosheath when IMF points radially. [ABSTRACT FROM AUTHOR]

Revealing the origins of aurorae in Earth's polar cap has long been a challenge since direct precipitation of energetic electrons from the magnetosphere is not always expected in this region of open magnetic field lines. Here, we introduce an exceptionally gigantic aurora filling the entire polar cap region on a day when the solar wind had almost disappeared. By combining ground-based and satellite observations, we proved that this unique aurora was produced by suprathermal electrons streaming directly from the Sun, which is known as "polar rain." High-sensitivity imaging from the ground has visualized complex spatial structures of the polar rain aurora possibly manifesting the internal pattern of the solar wind or even the organizations in the chromosphere of the Sun. [ABSTRACT FROM AUTHOR]

Numerical simulations have been an increasingly important tool in space physics. Here, we introduce an open-source three-dimensional compressible Hall-Magnetohydrodynamic (MHD) simulation code LAPS (UCLA-Pseudo-Spectral, https://github.com/chenshihelio/LAPS). The code adopts a pseudo-spectral method based on Fourier Transform to evaluate spatial derivatives, and third-order explicit Runge-Kutta method for time advancement. It is parallelized using Message-Passing-Interface (MPI) with a "pencil" parallelization strategy and has very high scalability. The Expanding-Box-Model is implemented to incorporate spherical expansion effects of the solar wind. We carry out test simulations based on four classic (Hall)-MHD processes, namely, 1) incompressible Hall-MHD waves, 2) incompressible tearing mode instability, 3) Orszag-Tang vortex, and 4) parametric decay instability. The test results agree perfectly with theory predictions and results of previous studies. Given all its features, LAPS is a powerful tool for large-scale simulations of solar wind turbulence as well as other MHD and Hall-MHD processes happening in space. [ABSTRACT FROM AUTHOR]

Lithium, a critical natural resource integral to modern technology, has influenced diverse industries since its discovery in the 1950s. Of particular interest is lithium-7, the most prevalent lithium isotope on Earth, playing a vital role in applications such as batteries, metal alloys, medicine, and nuclear research. However, its extraction presents significant environmental and logistical challenges. This article explores the potential for lithium exploration on the Moon, driven by its value as a resource and the prospect of cost reduction due to the Moon's lower gravity, which holds promise for future space exploration endeavors. Additionally, the presence of lithium in the solar wind and its implications for material transport across celestial bodies are subjects of intrigue. Drawing from a limited dataset collected during the Apollo missions (Apollo 12, 15, 16, and 17) and leveraging artificial intelligence techniques and sample expansion through bootstrapping, this study develops predictive models for lithium-7 concentration based on spectral patterns. The study areas encompass the Aitken crater, Hadley Rima, and the Taurus–Littrow Valley, where higher lithium concentrations are observed in basaltic lunar regions. This research bridges lunar geology and the formation of the solar system, providing valuable insights into celestial resources and enhancing our understanding of space. The data used in this study were obtained from the imaging sensors (infrared, visible, and ultraviolet) of the Clementine satellite, which significantly contributed to the success of our research. Furthermore, the study addresses various aspects related to statistical analysis, sample quality validation, resampling, and bootstrapping. Supervised machine learning model training and validation, as well as data import and export, were explored. The analysis of data generated by the Clementine probe in the near-infrared (NIR) and ultraviolet-visible (UVVIS) spectra revealed evidence of the presence of lithium-7 (Li-7) on the lunar surface. The distribution of Li-7 on the lunar surface is non-uniform, with varying concentrations in different regions of the Moon identified, supporting the initial hypothesis associating surface Li-7 concentration with exposure to solar wind. While a direct numerical relationship between lunar topography and Li-7 concentration has not been established due to morphological diversity and methodological limitations, preliminary results suggest significant economic and technological potential in lunar lithium exploration and extraction. [ABSTRACT FROM AUTHOR]

In this work, we find empirical evidence that the scale-dependent statistical properties of solar wind and magnetohydrodynamic (MHD) turbulence can be described in terms of a family of parametric probability distribution functions (PDFs) known as Normal Inverse Gaussian (NIG). Understanding these PDFs is one of the most important goals in turbulence theory, as they are inherently connected to the intermittent properties of solar wind turbulence. We investigate the properties of PDFs of Elsasser increments based on a large statistical sample from solar wind observations and high-resolution numerical simulations of MHD turbulence. In order to measure the PDFs and their corresponding properties, three experiments are presented: fast and slow solar wind for experimental data and a simulation of reduced MHD (RMHD) turbulence. Conditional statistics on a 23-yr-long sample of WIND data near 1 au and high-resolution pseudo-spectral simulation of steadily driven RMHD turbulence on a |$2048^3$| mesh are used to construct scale-dependent PDFs. The empirical PDFs are fitted to NIG distributions, which depend on four free parameters. Our analysis shows that NIG distributions accurately capture the evolution of the PDFs, with scale-dependent parameters, from large scales characterized by a Gaussian distribution, turning to exponential tails within the inertial range and stretched exponentials at dissipative scales. We also show that empirically-measured NIG parameters exhibit well-defined scaling properties that are similar across the three empirical data sets, which may be indicative of universal behaviour. [ABSTRACT FROM AUTHOR]

Traditional Martian bow shock and magnetic pileup (magnetopause) boundary models are based on the fitting of free parameters in a prescribed formula. The form of the formula, fitted data, and considered controlling parameters distinguish the individual models from each other. However, all these models have one thing in common: the shape of the boundary and the parametric dependence assumed are fixed by the prescribed formula. The fitted data set typically consists of individual identified boundary crossings. This approach can suffer from a significant bias, as the boundary crossings are more likely to be identified in regions where a spacecraft spends more time. In this study, we use an automated region classification of the data measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft to solar wind, magnetosheath, or magnetosphere. This is achieved by applying the Support Vector Machine method to individual spacecraft half-orbits (from periapsis to apoapsis or vice versa). Two different models of the locations of the bow shock and magnetic pileup boundaries are then constructed based on neural networks: i) a model trained using the classified data, and ii) a model trained using individual identified boundary crossings. As compared to formal empirical modeling efforts, the neural network models do not assume any prescribed shape/distance formula. Optimal model parameterization (considering the solar wind dynamic pressure, solar ionizing flux, crustal magnetic field magnitude, Alfvén Mach number, and interplanetary magnetic field magnitude) is discussed and the model performance evaluated. [ABSTRACT FROM AUTHOR]

Imaging missions in Earth Science, Heliophysics, and Astrophysics have made fundamental advancements in science and have helped to further our understanding of our natural environment. Here we review the Solar-Terrestrial Observer for the Response of the Magnetosphere (STORM) mission concept, a global solar wind-magnetosphere imaging mission and investigate how often STORM can observe and image its key science targets; the magnetopause, ring current, and auroral oval. We introduce a novel analysis which defines STORM's plasma targets as discrete sample points in space, these points are collectively called point groups. These point groups are used in conjunction with fields-of-view of STORM's imagers to quantify target visibility, how often the mission can observe each of its targets. The target visibility is combined with a statistical investigation of historical solar wind and geomagnetic data, and a k-folds/Monte Carlo analysis to quantify STORM's science visibility. That is how often specific targets can be observed during elevated solar wind and geomagnetic conditions such that detailed science investigations can be completed to address STORM's science objectives. This analysis is further expanded to potential dual-spacecraft mission configurations to determine the nominal inter-orbit phasing which maximizes target and science visibility. Overall, we find that the target and science visibility of a single spacecraft mission is large, in the 100s and 1000s of hours/events, while the target and science visibility peak for a dual-spacecraft mission where the two spacecraft are -85° out of phase. [ABSTRACT FROM AUTHOR]

Partially ionized plasmas (PIP) constitute an essential ingredient of our plasma universe. Historically, the physical effects associated with partial ionization were considered in astrophysical topics such as the interstellar medium, molecular clouds, accretion disks and, later on, in solar physics. PIP can be found in layers of the Sun's atmosphere as well as in solar structures embedded within it. As a consequence, the dynamical behaviour of these layers and structures is influenced by the different physical effects introduced by partial ionization. Here, rather than considering an exhaustive discussion of partially ionized effects in the different layers and structures of the solar atmosphere, we focus on solar prominences. The reason is that they represent a paradigmatic case of a partially ionized solar plasma, confined and insulated by the magnetic field, constituting an ideal environment to study the effects induced by partial ionization. We present the current knowledge about the effects of partial ionization in the global stability, mass cycle and dynamics of solar prominences. We revise the identified observational signatures of partial ionization in prominences. We conclude with prospects for PIP research in prominences, proposing the path for advancing in the prominence modelling and theory and using new and upcoming instrumentation. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Parametric coupling of waves is one of the most efficient mechanisms of energy transfer that can lead to the growth or decay of waves. This transfer occurs at frequencies close to their natural frequencies. In partially ionized solar plasma, there are a multitude of waves that can undergo this process. Here, we study the parametric coupling of Alfvén waves propagating in a partially ionized solar plasma with ionization-recombination waves identified by our study to appear in a plasma in ionization non-equilibrium. Depending on the parameters that describe the plasma (density, temperature), coupling can lead to a parametric resonance. Our study determines the occurrence conditions of parametric resonance, by finding the boundaries between stable and unstable regions in the parameter space. Our results show that collisions and non-equilibrium recombination can both contribute to the onset of unstable behaviour of parametrically resonant Alfvén waves. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

This study explores nonlinear development of the magnetized Rayleigh–Taylor instability (RTI) in a prominence-corona transition region. Using a two-fluid model of a partially ionized plasma, we compare RTI simulations for several different magnetic field configurations. We follow prior descriptions of the numerical prominence model (Popescu Braileanu et al. 2021 Astron. Astrophys.646, A93 (doi:10.1051/0004-6361/202039053), Popescu Braileanu et al. 2021 Astron. Astrophys.650, A181 (doi:10.1051/0004-6361/202140425) and Popescu Braileanu et al. 2023 Astron. Astrophys.670, A31 (doi:10.1051/0004-6361/202142996)) and explore the charged-neutral fluid coupling and plasma heating in a two-dimensional mixing layer for different magnetic field configurations. We also investigate how the shear in magnetic field surrounding a prominence may impact the release of the gravitational potential energy of the prominence material. We show that the flow decoupling is strongest in the plane normal to the direction of the magnetic field, where neutral pressure gradients drive ion-neutral drifts and frictional heating is balanced by adiabatic cooling of the expanding prominence material. We also show that magnetic field within the mixing plane can lead to faster nonlinear release of the gravitational energy driving the RTI, while more efficiently heating the plasma via viscous dissipation of associated plasma flows. We relate the computational results to potential observables by highlighting how integrating over under-resolved two-fluid sub-structure may lead to misinterpretation of observational data. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Turbulence is a fundamental process that drives mixing and energy redistribution across a wide range of astrophysical systems. For warm (T≈104 K) plasma, the material is partially ionized, consisting of both ionized and neutral species. The interactions between ionized and neutral species are thought to play a key role in heating (or cooling) of partially ionized plasmas. Here, mixing is studied in a two-fluid partially ionized plasma undergoing the shear-driven Kelvin–Helmholtz instability to evaluate the thermal processes within the mixing layer. Two-dimensional numerical simulations are performed using the open-source (PIP) code that solves for a two-fluid plasma consisting of a charge-neutral plasma and multiple excited states of neutral hydrogen. Both collisional and radiative ionization and recombination are included. In the mixing layer, a complex array of ionization and recombination processes occur as the cooler layer joins the hotter layer, and vice versa. In localized areas of the mixing layer, the temperature exceeds the initial temperatures of either layer with heating dominated by collisional recombinations over turbulent dissipation. The mixing layer is in approximate ionization-recombination equilibrium, however the obtained equilibrium is different to the Saha–Boltzmann local thermal equilibrium. The dynamic mixing processes may be important in determining the ionization states, and with that intensities of spectral lines, of observed mixing layers. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Solar partially ionized plasma is frequently modelled using single-fluid (1F) or two-fluid (2F) approaches. In the 1F case, charge-neutral interactions are often described through ambipolar diffusion, while the 2F model fully considers charge-neutral drifts. Here, we expand the definition of the ambipolar diffusion coefficient to include inelastic collisions (ion/rec) in two cases: a VAL3C one-dimensional model and a 2F simulation of the Rayleigh–Taylor instability (RTI) in a solar prominence thread based on [Lukin et al. 2024 Phil. Trans. R. Soc. A382, 20230417. (doi:10.1098/rsta.2023.0417)]. On one side, we evaluate the relative importance of the inelastic contribution, compared to elastic and charge-exchange collisions. On the other side, we compare the contributions of ion/rec, thermal pressure, viscosity and magnetic forces to the charge-neutral drift velocity of the turbulent flow of the RTI. Our analysis reveals that the contribution of inelastic collisions to the ambipolar diffusion coefficient is negligible across the chromosphere, allowing the classical definition of this coefficient to be safely used in 1F modelling. However, in the transition region, the contribution of inelastic collisions can become as significant as that of elastic collisions. Furthermore, we ascertain that the thermal pressure force predominantly influences the charge-neutral drifts in the RTI model, surpassing the impact of the magnetic force. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

The article discusses the importance of understanding the energy flow and dynamic motions in the solar atmosphere in order to uncover mysteries about the Sun, such as how it is heated and the formation of cool clouds called prominences. The majority of the fluid in the lower layers of the solar atmosphere is neutral, meaning it is not directly affected by magnetic fields. However, interactions between neutral particles and charged ions and electrons allow the magnetic field to couple with the neutrals and drive coherent dynamics. Recent advances in observational instruments and theoretical modeling have provided new insights into the physics of partially ionized plasma in the solar atmosphere. The article also highlights the need for a unified understanding of the underlying physical processes and the importance of studying partially ionized plasma in the formation, dynamics, and stability of solar prominences. The thematic issue of the journal aims to present the cutting edge of current research on partially ionized plasma in the solar atmosphere and provide a roadmap for future developments. [Extracted from the article]

The ambipolar diffusion approximation is used to model partially ionized plasma dynamics in a single-fluid setting. To correctly apply the commonly used version of ambipolar diffusion, a set of criteria should be satisfied including the requirement that the difference in velocity between charges and neutral species (known as drift velocity) is much smaller than the thermal velocity, otherwise the drift velocity will drive a non-negligible level of further collisions between the two species. In this paper, we explore the consequences of relaxing this assumption. We show that a new induction equation can be formulated without this assumption. This formulation reduces to the ambipolar induction equation in the case the drift velocity is small. In the large drift velocity limit, the feedback of the drift velocity on the collision frequency results in decreased diffusion of the magnetic field compared with the standard ambipolar diffusion approximation for the same parameters. This has a natural consequence of reducing the frictional heating that can occur. Applying this to results from flux emergence simulations where the expansion of the magnetic field leads to strong adiabatic cooling of the partially ionized chromosphere resulted in a noticeable reduction in the magnitude of the predicted drift velocities. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Partially ionized plasmas constitute an essential ingredient of the solar atmosphere, and ground- and space-based observations have pointed out the presence of oscillations in partially ionized solar plasmas such as chromosphere, photosphere, prominences or spicules, which have been interpreted in terms of magnetohydrodynamic waves. Our aim is to study the spatial behaviour of propagating weakly and fully nonlinear Alfvén waves, and the subsequent excitation of field-aligned motions and perturbations, when dissipative mechanisms, such as ambipolar diffusion and radiative losses, together with parametrized heating mechanisms, are taken into account. When only ambipolar diffusion is taken into account, first-order Alfvén waves as well as ponderomotive-driven perturbations are spatially damped, while field-aligned motions and perturbations representing propagating slow waves are undamped. These perturbations are damped when thermal effects are also considered and their damping lengths can be longer or shorter than those of ponderomotive-driven perturbations. Therefore, after the initial excitation, Alfvén waves and ponderomotive-driven perturbations could be quickly damped while slow waves still remain in the plasma, and vice versa. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

The cutoff effect is a significant determinant of solar magnetohydrodynamic wave propagation and hence pivotal in energy transfer studies, such as solar plasma heating and seismological diagnostics. Despite continuous efforts, no good agreement between observed waveperiods and theory or numerical simulations was found. Our objective is to investigate the magnetoacoustic cutoff effect in the partially ionized solar atmosphere, factoring in the two-fluid effects. We developed a two-fluid MHD numerical model and used it to simulate a quiet region of the Sun from the top of the convective zone to the low corona. Our findings show that the ongoing granulation excites a wide range of waves propagating into the upper atmospheric layers. The cutoff waveperiods strongly depend on the height. Two-fluid waveperiods obtained with numerical simulations reproduce the recent observations at a very good level of compliance. Furthermore, direct comparison with strongly coupled cases that imitate the single-fluid approximation have shown that the waveperiod propagation pattern is only present in fully two-fluid simulations. We conclude that the presence of neutrals and therefore collisional terms change the dynamics of the magnetized plasma, in comparison with the single-fluid approximation. This effect is more prominently seen in the upper photosphere and chromosphere. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review of recent theoretical investigations concerning magnetohydrodynamic (MHD) waves in partially ionized solar plasma. First, we examine the properties of linear MHD waves in a uniform partially ionized plasma and discuss the relevant effects arising from partial ionization. Subsequently, we delve into MHD wave studies in the more intricate settings of the lower solar atmosphere and solar prominences. These investigations involve topics such as MHD waves in magnetic flux tubes, wave excitation, linear and nonlinear mode coupling and wave heating. We outline new challenges that future research should tackle. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

We present the formation of quasi-periodic cool spicule-like jets in the solar atmosphere using 2.5-D numerical simulation in two-fluid regime (ions+neutrals) under the presence of thermal conduction and ion-neutral collision. The nonlinear, impulsive Alfvénic perturbations at the top of the photosphere trigger field aligned magnetoacoustic perturbations due to ponderomotive force. The transport of energy from Alfvén pulse to such vertical velocity perturbations due to ponderomotive force is considered as an initial trigger mechanism. Thereafter, these velocity perturbations steepen into the shocks followed by quasi-periodic rise and fall of the cool jets transporting mass in the overlying corona. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

The plasma in cool cores of solar prominences is partially ionized and its ionization degree, in general, depends on the actual kinetic temperature and density of the plasma and the ions considered. However, we demonstrate that under typical prominence conditions, the dominant mechanism contributing to partial ionization is photoionization by radiation diffusing through the plasma. This mechanism strongly depends on the radiation illuminating prominences from the surrounding solar atmosphere. The understanding of the partial ionization of prominence plasma thus requires a complex solution of the non-LTE radiative-transfer problem. In this paper, we discuss the ionization of hydrogen, helium and some other important species. We also demonstrate the role of non-equilibrium ionization. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

In this paper, we study the role of radiative cooling (RC) in a two-fluid model consisting of coupled neutrals and charged particles. We first analyse the linearized two-fluid equations where we include radiative losses in the energy equation for the charged particles. In a one-dimensional geometry for parallel propagation and in the limiting cases of weak and strong coupling, it can be shown analytically that the instability conditions for the thermal mode and the sound waves, the isobaric and isentropic criteria, respectively, remain unchanged with respect to one-fluid radiative plasmas. For the parameters considered in this paper, representative for the solar corona, the RC produces growth of the thermal mode and damping of the sound waves. In the weak coupling limit, the growth of the thermal instability and the damping of the sound waves is as derived in Field (Field 1965 Astrophys. J.142, 531 (doi:10.1086/148317)) using the charged fluid properties. When neutrals are included and are sufficiently coupled to the charges, the thermal mode growth rate and the wave damping both reduce by the same factor, which depends on the ionization fraction only. For a heating function that is constant in time, we find that the growth of the thermal mode and the damping of the sound waves are slightly larger. The numerical calculation of the eigenvalues of the general system of equations in a three-dimensional geometry confirm the analytic results. We then run two-dimensional fully nonlinear simulations that give consistent results: a higher ionization fraction or lower coupling will increase the growth rate. The magnetic field contribution is negligible in the linear phase. Ionization-recombination effects might play an important role because the RC produces a large range of temperatures in the system. In the numerical simulation, after the first condensation phase, when the minimum temperature is reached, the fraction of neutrals increases four orders of magnitude because of the recombination. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

The solar wind (SW) plasma thermodynamics in the solar corona is determined by the energy exchange with external sources and can be studied if information about physical plasma parameters, such as the SW temperature, density, flow velocity, etc., is known. Previously, Parker showed that within the one-fluid model the SW plasma state could be described by a polytropic function in which the pressure and density are related by the relation with the polytropic index . In present-day MHD models the application of a polytropic function instead of an approximate description of the plasma heating mechanisms speeds up the computation considerably. The polytropic index can be estimated using the SW plasma parameters, but for the SW flows moving toward the Earth measuring such parameters presents certain difficulties. In this paper we consider a method to determine the polytropic index for the SW flows at the stage of expansion in the corona from the SW plasma ion parameters measured in situ: the mean Fe ion charge and the ion density ratio. The relation between the ion parameters and the polytropic index is established by solving the balance equations for the ionization and recombination processes in the SW plasma. The mean values of in the corona at heights of 1–7 solar radii for the flows of the slow SW, the fast SW from coronal holes, and interplanetary coronal mass ejections have been obtained from the histograms of the SW ion parameters measured with the ACE/SWICS instrument in 2010. [ABSTRACT FROM AUTHOR]

Geophysical processes in the region of the dayside polar cusp on December 22, 2003, were studied for a northern orientation of the interplanetary magnetic field (IMF) and a relatively high-velocity, low-density solar wind, using ground-based optical observations in Svalbard and DMSP F16 satellite data. Comparison of satellite and ground-based observations shows that soft electron precipitation in the cusp region determines the auroral glow in the 630.0 nm (OI) emission. The peculiarity of the considered event is observation of a bright rayed arc of the aurora rimming the dayside cusp from its polar edge. The results of observations by the low-flying DMSP F16 satellite as it intersected the rayed arc were analyzed. Explanations for the observed phenomena are proposed, based on analysis of changes in the spectra of precipitating electrons and formation of a field-aligned electron beam by the field-aligned electric field. [ABSTRACT FROM AUTHOR]

The auroral electrojet index AE is often used in forecasting models as a driver of the disturbance propagation in the geosphere from the pole to middle and low latitudes. However, these data are not available digitally since January 2020. Instead of the AE-index, we suggest using the recently introduced 1 h Apo-index, given the close proximity of magnetometer networks for these indices at high latitudes and the availability of the Apo-index in real time. To this end their correlation is analyzed during 276 intense storms for 1995–2017. Storm profiles are constructed by method of superposed epochs with zero epoch time t0 = 0 taken at the threshold value of AE ≥ 1000 nT. A comparison is made of the storm profiles of AE(t), Apo(t), the interplanetary electric field E(t) and the solar wind speed Vsw(t) within 72 h: 24 h before the storm peak t0, and 48 h afterward. A good agreement is obtained between the sets of AE(t) and Apo(t) with a correlation coefficient of 0.70. Comparison with the interplanetary parameters testifies on the correlation of AE(t) and Apo(t) with the electric field E(t) but missing their linkage with the solar wind speed Vsw(t). A two-parametric formula is derived for dependence of the auroral electrojet index AE(t) on the interplanetary electric field E(t) and the geomagnetic Apo(t) index for the geomagnetic storm forecasting. In the absence of E(t) data, formulae for the dependence of AE(t) on Apo(t) is introduced for implementation in real time and the inverse dependence of Apo(t) on AE(t) for reconstruction of the 1 h Apo-index before 1995. Validation of the proposed models with data for 5 intense storms in 2018 has shown a close resemblance of the model with observation data of the AE-index with a high coefficient of determination R 2 ranging from 0.62 to 0.81. [ABSTRACT FROM AUTHOR]

Space plasma turbulence plays a relevant role in several plasma environments, such as solar wind and the Earth's magnetosphere–ionosphere system, and is essential for describing their complex coupling. This interaction gives rise to various phenomena, including ionospheric irregularities and the amplification of magnetospheric and ionospheric currents. The structure and dynamics of these currents have relevant implications, for example, in studying ionospheric heating and the nature of electric and magnetic field fluctuations in the auroral and polar environments. In this study, we investigate the nature of small-scale fluctuations characterizing the ionospheric magnetic field in response to different geomagnetic conditions. We use high-resolution (50 Hz) magnetic data from the ESA's Swarm mission, collected during a series of high-latitude crossings, to probe the scaling features of magnetic field fluctuations in auroral and polar cap regions at spatial scales still poorly explored. Our findings reveal that magnetic field fluctuations in field-aligned currents (FACs) and polar cap regions across both hemispheres are characterized by different scaling properties, suggesting a distinct driver of turbulence. Furthermore, we find that geomagnetic activity significantly influences the nature of energy dissipation in FAC regions, leading to more localized filamentary structures toward smaller scales. [ABSTRACT FROM AUTHOR]

The goal of this effort is to monitor and manage a hybrid stand-alone photovoltaic (PV) and wind energy system (WES) using the Internet of Things (IoT). The suggested hybrid system uses Incremental Conductance (INC) Maximum Power Point Tracking (MPPT) and Perturb and Observe (P&O)-based Sliding Mode Control (SMC) approaches. The cost-effective Arduino Uno board in Matlab is used to analyze the P&O and INC MPPT methods. Energy from renewable sources is stored in a battery, and the output voltage of each source is monitored using the blynk app and GSM 800c module. Simulation results validate the controller's operation, and the performance of both MPPT algorithms is compared. Experimental outcomes demonstrate the effectiveness of the IoT-based controller and its characteristic functionalities. Overall, this proposed hybrid PV and WES configuration offers advantages such as reduced human resources, cost-effectiveness, time savings, enhanced reliability, and improved data collection and control capabilities. [ABSTRACT FROM AUTHOR]

The renewed interest in nonlinear wave–wave coupling phenomena is motivated by the observations of radiation belt storm probes (RBSP) in the Earth's magnetosphere. The recent studies on this subject are mainly limited to the qualitative explanations of RBSP satellites observations. In magnetized plasmas like solar wind, Earth's magnetosphere and many astrophysical environments electrons and ions spiraling along magnetic field lines during cyclotron motion can interfere with the turbulent wave–wave coupling phenomena. This work quantitatively shows that cyclotron resonance plays a complementary role in understanding the turbulent wave–wave coupling in magnetized plasma. It is considered that electrons are in cyclotron resonance with very-low-frequency (VLF) waves, which are coupled with Langmuir oscillations and ultra-low-frequency (ULF) waves. Several illustrative examples are presented. It is found that the resonant electron pitch angles and energy seriously affect the coupling of VLF, ULF, and Langmuir waves. Our findings are important for understanding turbulence in magnetotail region of Earth's magnetosphere. [ABSTRACT FROM AUTHOR]