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Three-dimensional global hybrid simulations are performed to explore how the interplanetary magnetic field (IMF), the Martian crustal fields, and planetary pickup ions affect the twisting of the Martian magnetotail. The results agree with previous studies that the crustal magnetic fields cause the Martian magnetotail to twist counterclockwise or clockwise depending on the sign of the IMF Y -component in the Mars solar orbital coordinates. However, the twist is more pronounced when the crustal fields are on the nightside, contradicting the early explanation that the crustal fields affect the twist through dayside magnetic reconnection between the crustal fields and the draped IMF. Additionally, planetary pickup ions also contribute to the twist because their mass loading slows down the plasma flow and leads to the bending of the magnetic field lines in the magnetotail. It is demonstrated that the twist inside Mars' shadow in the near magnetotail region (at X = −1.5 R M, where R M is Mars' radius) is mainly attributable to the crustal fields, while the influence of planetary pickup ions starts to dominate outside Mars' shadow and in regions further away from Mars. [ABSTRACT FROM AUTHOR]

The orientation of Interplanetary Magnetic Field (IMF B) components plays a major role in magnetospheric Energetic Particles Precipitation (EPP). This is because the IMF B components in the Geocentric Solar Magnetospheric (GSM) coordinate system control magnetic reconnection at the subsolar magnetopause. This study intends to unravel the dependence of the preceding conditions of the orientations of IMF B components that drove geomagnetic storms on the EPPs produced in the Van Allen radiation belt. We classified the geomagnetic storms based on their drivers and IMF B z orientations prior to the storms' onset. Energetic particle fluxes, IMF B, and solar wind data were used. The study showed that electrons are more reactive to solar wind speed than protons. Additionally, storms with southward IMF B z orientation caused more EPP enhancement than with northward orientation. Our results also showed that protons are more influenced by magnetospheric compression than electrons at the northward orientation of IMF B z. In fact, at this point, the proton's motion violates adiabatic invariants. As particles interact with electric fields, a significant population of EPPs is produced by pitch angle diffusion. Generally, IMF B x and IMF B y are often anticorrelated. The preceding conditions of orientations of the IMF B x indicated weaker dependence on auroral indices, and invariably on energetic particles precipitation than the IMF B y. [ABSTRACT FROM AUTHOR]

The foreshock region filled with turbulences is a natural lab for studying interactions between plasma and waves. The underlying processes are vital for dissipating the energy carried by the solar wind into the Martian environment. In this study, we analyze an ultralow-frequency wave observed on 2015 August 14 by Mars Atmosphere and Volatile Evolution upstream of the Martian bow shock. The wave properties match with those of 30 s waves; the dispersion calculation shows that the upstream plasma was capable of generating the observed waves. The analysis of the ion behaviors implies the wave generated without a field-aligned beam, while the growth rate of waves seems to be modulated by the interplanetary magnetic field conditions. These results indicate the unique role of the Martian foreshock in the interaction between the solar wind and the planet. [ABSTRACT FROM AUTHOR]

The accurate knowledge of cosmic ion fluxes is essential for fundamental physics, deep space missions, and exploration activities in the solar system. In the HelMod-4 model the Parker transport equation is solved using a Monte Carlo approach to evaluate the solar modulation effect on local interstellar spectra of Galactic Cosmic Rays (GCRs). This work presents the latest updates to the HelMod-4 model parameters, focusing on the descending phase of solar cycle 24. The updates are motivated by the latest high-precision measurements from the AMS-02 detector which revealed for the first time with high accuracy the features of GCR fluxes' evolution during a period of positive interplanetary magnetic field polarity. Furthermore, we present HelMod-4/CUDA , a GPU-accelerated approach for solving the Parker equation in the heliosphere using a stochastic differential equation method. The code is an evolution of the HelMod-4 code, porting the algorithm to GPU architecture using the CUDA programming language. This approach achieves significant speedup compared to a CPU implementation. The HelMod-4/CUDA code has been validated by comparing its results with the most precise and updated experimental GCR spectra observed during high and low solar activity periods, both in the inner and outer heliosphere, at the Earth location, and outside the ecliptic plane. The comparison shows that HelMod-4 and HelMod-4/CUDA can be equivalently used to provide solar-modulated spectra with a similar degree of accuracy in reproducing observed data. [ABSTRACT FROM AUTHOR]

Alfvén waves are important carriers of solar wind energy into the Earth's magnetosphere and upper atmosphere. The observed distribution of Alfvénic power at low altitude exhibits significant dawn‐dusk asymmetry with different causes and impacts on the dayside and nighside. The nightside asymmetry has been shown to be controlled by the meridional gradient in the ionospheric Hall conductance. It is not clear what controls the dayside asymmetry. Both the ionospheric conductance gradient and orientation of the y‐component of the interplanetary magnetic field (IMF) are possible factors. We examined both possibilities using global magnetohydrodynamic (MHD) simulations. Our results show: (a) The dayside distribution of Alfvénic power is very sensitive to the orientation of IMF By, with enhanced power in the dawn (dusk) sector of the northern hemisphere for positive (negative) By (and opposite in the southern hemisphere); and (b) gradients in ionospheric conductance exert a weaker influence on the dayside asymmetry. Plain Language Summary: Alfvénic energy flux, which has an important impact on the low‐altitude space environment, is observed to be enhanced in the postnoon (prenoon) sector relative to prenoon (postnoon). In this study, we use global MHD simulations to determine the extent to which the dayside asymmetry in Alfvénic energy flux is controlled by the interplanetary magnetic field (IMF) and gradients in ionospheric conductance. Most of the dayside Alfvénic power is generated on open magnetic field lines, so we might expect the IMF By component to exert a significant influence on pre/postnoon flux distributions. The simulation experiments confirm this expectation and further show that the effects of gradients in ionospheric conductance are comparatively weaker. The results explain why some satellite observations on average exhibit a asymmetric enhancement in Alfvénic energy fluxes. Key Points: Dawn‐dusk asymmetry in dayside Alfvénic power is due to different magnetic field configurations associated with the direction of IMF ByIonospheric conductance contributes less to the asymmetric dayside Alfvénic Poynting flux distribution around noon [ABSTRACT FROM AUTHOR]

The high latitude ionospheric evolution of the May 10‐11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150–300 km, reaching levels of up to 630 km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2‐layer on the eleventh, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the eleventh. Plain Language Summary: The intense geomagnetic storm of May 2024 caused a plethora of different responses within the Earth's ionosphere. In the early phases of the storm, the auroral oval quickly expands to upper midlatitudes and induces strong variations in Global Navigation Satellite System (GNSS) phase measurements. Concurrently, midlatitude plasma is repeatedly lifted by 100–300 km on timescales of about an hour resulting in enhanced plasma densities. This intensified and lifted plasma is then drawn into the polar cap inducing variations in GNSS amplitude and phase. As the storm evolves, heating drives mixing of the thermosphere and causes an extreme depletion in ionospheric plasma. After 24 hr, despite severe geomagnetic conditions persisting, the depleted plasma environment results in only relatively weak plasma transport into the polar cap and significantly reduced impacts on GNSS. Key Points: Plasma lifting during the storm caused midlatitude displacements of ionospheric peak height by as much as 300 km over the course of 1 hourSporadic‐E is observed at the sub‐auroral convective boundary edge of the storm‐enhanced density with strong plasma drift shears presentSevere depletion of electron density at mid and high latitudes significantly reduced the impact of subsequent geomagnetic activity on GNSS [ABSTRACT FROM AUTHOR]

This study aims to improve the understanding of geomagnetic storms by utilizing machine learning models and analyzing several heliophysical variables, such as the interplanetary magnetic field, proton density, solar wind speed, and proton temperature. Rather than relying on traditional correlation-based methods, we employ advanced machine learning techniques to examine the complex relationships between these factors and geomagnetic storms. Our analysis covers a large dataset spanning six solar cycles, including the current 25th cycle, to provide comprehensive insights into the dynamics of these storms. Our study highlights the significance of the interplanetary magnetic field as a key predictor of geomagnetic storms, challenging previous beliefs that primarily focused on sunspot activity. By using high-resolution data, we uncover new patterns and provide a more detailed analysis of the factors influencing geomagnetic storms. We emphasize the importance of considering a range of heliophysical variables, such as proton temperature and flow pressure, which offer new insights into the complex dynamics driving these storm events. The application of machine learning models, particularly Random Forest and Gradient Boosting, demonstrated superior predictive accuracy compared to traditional methods. Our results reveal that the Dst-index MIN, scalar B, and alpha/proton ratio are among the most influential factors, accounting for a significant portion of the prediction model's accuracy. These findings underscore the utility of machine learning in identifying critical drivers of geomagnetic activity and enhancing forecast precision. Additionally, our research underscores the need for comprehensive models that can accurately predict geomagnetic storms by integrating various data sources. This machine learning approach not only improves predictive accuracy but also enhances our understanding of the underlying mechanisms of space weather. The insights gained from this study have important implications for both scientific research and practical applications, such as improving early warning systems for geomagnetic storms and mitigating their potential impacts on Earth. [ABSTRACT FROM AUTHOR]

In this research, the validity of Bernoulli's theorem for the solar wind crossing the Earth's bow shock has been investigated based on space explorations. Using solar wind plasma and interplanetary magnetic field data from the OMNI database, along with magnetosheath plasma and magnetic field data measured by the magnetospheric multiscale satellite in 2016 and 2018, 95 events were selected to study the Bernoulli invariant from the upstream to the downstream of Earth's bow shock (from the unshocked solar wind region to the shocked magnetosheath region). Statistical investigations show that the differences in the characteristic energy of plasmas between the solar wind region and the magnetosheath region are less than 5%, regardless of the upstream solar wind speed and the satellite's location in the magnetosheath. These results quantitatively support the generalization of Bernoulli's equation to the solar wind flowing through the bow shock, including the contribution of magnetic field energy. [ABSTRACT FROM AUTHOR]

Flux transfer events (FTEs) are magnetic structures generally believed to originate from time-varying magnetic reconnection at the Earth's magnetopause. Despite years of research, the mechanism of how FTEs are formed through reconnection remains controversial. In various models, FTEs exhibit different global configurations. Studying the FTE axial orientation can provide insights into their global shape, thereby helping to distinguish the generation mechanisms. In this paper, taking advantage of the orbital characteristics of the four Cluster spacecraft, we devised a multi-spacecraft timing method to determine the axes of a total of 57 FTEs observed sequentially by Cluster during a high-latitude duskside magnetopause crossing. During the nearly five-hour observation, the interplanetary magnetic field (IMF) experienced a large rotation, leading to a substantial rotation of the magnetosheath magnetic field. The analysis results show two new features of the FTE axis that have not been reported before: (1) the axes of the FTEs gradually rotate in response to the turning of the IMF and the magnetosheath magnetic field; (2) the axes of the FTEs vary between the direction of the magnetosheath magnetic field and the direction of the reconnection X-line. These features indicate that FTEs may have a more complex global configuration than depicted by traditional FTE models. [ABSTRACT FROM AUTHOR]

In this study, we develop a robust real‐time forecast system for the SYM‐H index using Deep Neural Networks and real‐time Solar Wind measurements along with Interplanetary Magnetic Field parameters. This system provides not only one‐off forecasts but also quantile‐based confidence intervals, offering a range within which the observed SYM‐H values are expected to fall, enhancing forecast reliability and usability. The model is tested both on historical level 2 science‐ready data and on preliminary observations, which are closer to the operational environment that the model is expected to work on, demonstrating the model's robustness and practical utility in real‐time scenarios. The integration of quantile forecasts into SYM‐H prediction models represents a significant advancement, providing decision‐makers with more accurate and trustworthy information to manage the hazard of geomagnetic storms. Plain Language Summary: Geomagnetic storms can disrupt many of the systems modern society relies on, such as power grids, satellite operations, Global Navigation Satellite Systems and communication networks. These disturbances occur when the Earth's magnetic field interacts with the Solar Wind. To predict these events more accurately, we developed a forecasting system using machine learning. This system uses real‐time measurements from space probes to predict the SYM‐H index, an important indicator of geomagnetic activity. Our model not only predicts the expected values but also provides a range of possible outcomes, helping decision‐makers understand the uncertainty in the forecasts. This is especially useful in critical situations where accurate and timely information is needed to prepare for severe geomagnetic storms. The model has been tested with both curated historical data and preliminary observations, showing that it can reliably function in real‐world operational settings. This improvement in forecasting will help protect technological systems from the adverse effects of geomagnetic storms by providing more accurate and useful information for decision‐makers. Key Points: For a trustworthy forecast, it is required to provide a confidence interval that depends on the index intensityWe operationalize the use of new training, validation and test sets and a new evaluation metricWe define a test set for evaluation on a near real‐time operational scenario using provisional data from six recent low and moderate storms [ABSTRACT FROM AUTHOR]

The response of the thermosphere ionosphere system to an X1.3 class solar flare is studied using observations of the total electron content (TEC) and the Global Ionosphere Thermosphere Model (GITM) simulations. The solar flare erupted from the active region AR12975 on 30 March 2022. Owing to the absence of accompanying severe geomagnetic activity, it was possible to isolate the effects of the flare on the upper atmosphere. TEC data are processed for Continental USA (CONUS), employing filtering and binning techniques to create 2D variation maps. The spectral content of the TEC variations is analyzed using a wavelet coherence method. The immediate response of the solar flare exhibited broad similarities, while notable differences were observed during the recovery period between the East and West sides of the CONUS. GITM is used to explore the East–West asymmetry of the key T‐I parameters. Simulation results reveal that the coinciding interplanetary magnetic field southward turning had a greater influence on these parameters compared to the solar flare, while their nonlinear interaction introduced complex variations. Additional investigation reveals gravity wave damping also contributes to the asymmetric solar flare response. Plain Language Summary: This study examines how a solar flare, which erupted on 30 March 2022, affected the Earth's upper atmosphere. We used satellite data to measure changes in the amount of charged particles in the atmosphere above the United States (specifically the area known as CONUS) and ran computer simulations to better understand these changes. We found that while the immediate reaction of the atmosphere to the flare was similar across the CONUS, differences emerged between the East and West during the recovery phase. The simulations showed that these differences were influenced by local time differences between the East and West, as well as by variations in the Earth's magnetic field geometry above these regions. Additionally, the study identified that the damping of gravity waves also played a role in these regional differences. Overall, the research highlights how complex interactions between various factors can lead to different responses to solar events in different parts of the CONUS. Key Points: Spectral content and temporal variation of total electron content perturbations associated with an X1.3 Solar Flare are analyzedThe thermosphere‐ionosphere exhibits a longitudinal flare response during the recovery phaseThe nonlinear interaction of the solar flare with the southward turning of the interplanetary magnetic field Bz ${\mathrm{B}}_{z}$ introduces significant variability [ABSTRACT FROM AUTHOR]

The present study investigates mid‐ and low‐latitude ground magnetic disturbances observed following the arrival of three interplanetary (IP) shocks during the super‐geomagnetic storms of February 1958 and July 1959. One may expect that after IP shocks, the H (northward) magnetic component increases globally but especially on the dayside. However, in each event, the H component was depressed sharply for 1–2 hr in the dawn‐to‐noon sector, whereas it increased in other local time (LT) sectors. Observed magnetic deflections suggest that there existed field‐aligned currents (FACs) flowing into and out of the auroral zone around the western and eastern edges of the LT sector of the dayside H depression. These features strongly suggests that the observed H depression was a remote effect of a R1‐sense FAC system. It was previously reported that similar ground magnetic disturbances were observed after the SSC of the 2003 Halloween storm, which reveals striking similarities to the well‐known H depression observed at Colaba during the 1859 Carrington storm. It is therefore suggested that the external driving behind IP shocks, especially those associated with major storms, is most optimum for the sharp reduction of the dayside H component through the formation and intensification of the dayside FAC system. Associated magnetic disturbances are considered to be larger in magnitude with increasing magnetic latitude, and oriented azimuthally as well as meridionally. Such magnetic disturbances in dayside midlatitudes may not be discussed very often as a target of space weather, but their potential impacts on ground infrastructures probably require closer attention. Plain Language Summary: Geomagnetic storms of February 1958 and July 1959 were historically intense. After the arrival of interplanetary (IP) shocks during these storms, the horizontal component of midlatitude magnetic field was sharply depressed at prenoon, but at other local times (LTs) it enhanced significantly as generally expected from solar wind compression. This LT distribution of magnetic disturbances can be explained by a dayside wedge‐shaped current circuit, which connects the magnetosphere with the ionosphere. Similar ground magnetic disturbances were reported previously for the October 2003 (Halloween) storm, and the extraordinary H depression observed at Colaba during the 1859 Carrington storm was also observed when Colaba was at prenoon. It is therefore suggested that the driver of this dayside current system, probably southward interplanetary magnetic field, often becomes extraordinarily large behind IP shocks, especially those of major storms, and intensifies this current system to unusual levels. The associated magnetic disturbance is expected to be larger at higher latitudes, and oriented in any direction. These features exhibit a distinct contrast to magnetic disturbances caused by other magnetospheric current systems (e.g., the ring current). Dayside ground magnetic disturbances are rarely discussed as a potential cause of hazardous space weather events, but probably deserve closer attention. Key Points: The H magnetic component was depressed sharply in dayside mid‐ and low latitudes following IP shock arrivals during the 1958 and 1959 stormsThe H depression was confined from dawn to noon, and the direction of magnetic deflection depended on local time as expected for an R1 field‐aligned current (FAC) systemFor extreme solar wind driving, this dayside R1 FAC system can be a potential cause of geomagnetic hazards especially in the subauroral zone [ABSTRACT FROM AUTHOR]

Although initially it was presumed that foreshock waves would propagate directly into the dayside magnetosphere, observational evidence for sinusoidal Pc3 waves in the downstream of quasi‐parallel shocks is scarce. The transmission of these waves from the foreshock into the magnetosphere remains uncertain. In this paper, we employ a 3D global hybrid simulation at a realistic scale to explore the generation and transmission of the dayside ULF waves under a radial interplanetary magnetic field. Our findings demonstrate that the Pc3 waves are self‐consistently generated in the foreshock region and then transmitted into the magnetosheath and magnetosphere. In the foreshock, the waves are excited at approximately 25 mHz and exhibit right‐handed helicity in the plasma frame, characterizing them as quasi‐parallel fast magnetosonic waves. In the magnetosphere, the fluctuating magnetic field is mainly parallel to the background magnetic field, which indicates the dominant wave modes are compressional. Fluctuations in the magnetosheath show a broader spectrum (10–100 mHz) compared to those in the magnetosphere and foreshock, potentially explaining the little observation of sinusoidal Pc3 waves in the magnetosheath. Additionally, only lower frequency compressional waves (below 30 mHz) are effectively transmitted into the dayside magnetosphere. Our simulation provides critical insights into the interactions between the solar wind and Earth's magnetosphere. Plain Language Summary: Ultralow frequency waves in the Pc3 range, with periods of 10–45 s, are frequently detected in the Earth's magnetosphere. These waves are thought to originate from ion foreshock regions upstream of Earth's quasi‐parallel bow shock. They arise from ion beam instabilities triggered by the interaction between shock‐reflected suprathermal ions and the incoming solar wind. While it was assumed that these Pc3 waves would directly enter the dayside magnetosphere, in‐situ observations of sinusoidal Pc3 waves in the magnetosheath remain rare. This scarcity of evidence has left the mechanisms of their propagation into the magnetosphere unclear. This paper employs a 3D global hybrid simulation at a realistic scale to investigate how the Pc3 waves are transmited through the bow shock, magnetosheath, and into the magnetosphere under a radial interplanetary magnetic field. Our results indicate that the Pc3 waves are self‐consistently generated in the foreshock and transmitted into the magnetosheath and magnetosphere, with only lower frequency compressional waves effectively propagating into the magnetosphere. Fluctuations in the magnetosheath exhibit a broader spectrum compared to those in the magnetosphere and foreshock. Key Points: A 3D global hybrid simulation at a realistic scale has been used to investigate the dayside ULF waves under a radial interplanetary magnetic fieldPc 3 waves are self‐consistently generated at the foreshock region and transmitted into the magnetosheath and magnetosphereFluctuations in the magnetosheath exhibit a broad spectrum, and only lower frequency compressional waves are effectively transmitted into the magnetosphere [ABSTRACT FROM AUTHOR]

To understand the entry of the cool low‐latitude mantle ions into the tail plasma sheet near the flanks under persistent interplanetary magnetic field By, we evaluate the role of the cross‐field diffusive transport by kinetic Alfvén waves (KAWs) by investigating two events observed by multiscale (MMS) spacecraft. Around the separatrix between the open and closed field‐line regions, a two‐component mixing of hot plasma sheet ions of a few keV with cool mantle ions of a few hundred eV was observed, indicating transport across the separatrix. The waves observed between 0.01 and 10 Hz around the separatrix had characteristics consistent with those of KAWs. The consistency allowed us to estimate the wave vectors as a function of frequency by fitting KAW dispersion to the observations. Using the observed wave powers, plasma moments, and the estimated wave vectors, we computed the cross‐field diffusion rates associated with KAWs. The diffusion rates were found to be comparable to or larger than the Bohm diffusion rates during the intervals when the two‐component mixing was observed, indicating that the KAW diffusive transport can play a role in the entry of low‐latitude mantle ions into the plasma sheet. Key Points: We investigate cross‐field diffusive transport for the mixing of cold low‐latitude mantle ions and hot plasma sheet ions observed by MMSThe waves around the separatrix between the low‐latitude mantle and plasma sheet show the characteristics of kinetic Alfvén waves (KAWs)Estimated diffusive transport rates through KAWs are sufficiently large to cause the observed ion mixing [ABSTRACT FROM AUTHOR]

Magnetic reconnection changes the magnetic field topology and facilitates the energy and particle exchange at magnetospheric boundaries such as the Earth's magnetopause. The flow shear perpendicular to the reconnecting plane prevails at the flank magnetopause under southward interplanetary magnetic field conditions. However, the effect of the out‐of‐plane flow shear on asymmetric reconnection is an open question. In this study, we utilize kinetic simulations to investigate the impact of the out‐of‐plane flow shear on asymmetric reconnection. By systematically varying the flow shear strength, we analyze the flow shear effects on the reconnection rate, the diffusion region structure, and the energy conversion rate. We find that the reconnection rate increases with the upstream out‐of‐plane flow shear, and for the same upstream conditions, it is higher at the dusk side than at the dawn side. The diffusion region is squeezed in the outflow direction due to magnetic pressure which is proportional to the square of the Alfvén Mach number of the shear flow. The out‐of‐plane flow shear increases the energy conversion rate J·E′ $\boldsymbol{J}\cdot {\boldsymbol{E}}^{\prime }$, and for the same upstream conditions, the magnitude of J·E′ $\boldsymbol{J}\cdot {\boldsymbol{E}}^{\prime }$ is larger at the dusk side than at the dawn side. This study reveals that out‐of‐plane flow shear not only enhances the reconnection rate but also significantly boosts energy conversion, with more pronounced effects on the dusk‐side flank than on the dawn‐side flank. These insights pave the way for better understanding the solar wind‐magnetosphere interactions. Key Points: The reconnection rate increases with the out‐of‐plane flow shear and is higher at dusk than at dawn side for the same upstream conditionsThe diffusion region is squeezed in the outflow direction, causing its length to decrease as the out‐of‐plane shear flow increasesThe energy conversion rate increases with flow shear strength and is higher at dusk than at dawn side for the same upstream conditions [ABSTRACT FROM AUTHOR]

This study uses satellite measurements of plasma densities and thermospheric winds to analyze the effects of the November 2021 geomagnetic storm on ionospheric pre‐midnight topside plasma bubbles over South America. Using observations from the Ionospheric Connection Explorer (ICON) and the Global‐scale Observations of the Limb and Disk (GOLD) satellites, we find that pre‐midnight topside plasma bubbles were inhibited over eastern South America during the recovery phase of the storm. This is particularly notable because of the otherwise high occurrence rate of plasma bubbles at these longitudes during this season. This inhibition coincided with the recovery phase of the geomagnetic storm, marked by a northward turning of the z‐component of the interplanetary magnetic field (IMFBz) and quiet‐time values of the SuperMAG Auroral Electrojet Index (SME). We observed a westward turning of the zonal wind before the bubble inhibition, so we conclude the inhibition of topside plasma bubbles is likely related to a westward disturbance dynamo electric field (DDEF) causing a downward E×B $\mathbf{E}\times \mathbf{B}$ drift and suppress the growth of the instability responsible for bubble development. Contrary to theoretical predictions, we do not observe notable changes to the meridional wind during the event. These results provide new insights into the ionosphere‐thermosphere system's response to geomagnetic storms and highlight the role of wind patterns in inhibiting ionospheric irregularities, contributing to better predictive models for these phenomena. Plain Language Summary: Geomagnetic storms negatively affect communication and navigation systems by producing unpredictable changes in ionospheric densities. Plasma bubbles are irregularities in the ionosphere that occur mainly in the equatorial region and may be affected by geomagnetic storms. Studying plasma bubbles is crucial because they can significantly reduce the performance of communication and navigation systems, leading to signal loss or degradation. We conducted a study on how a geomagnetic storm in November 2021 affected the occurrence of pre‐midnight plasma bubbles over South America. Using data from two satellites (ICON and GOLD), we observed that these plasma bubbles disappeared during the storm's recovery phase. Our analysis suggests that this inhibition is likely linked to changes in wind patterns in the ionosphere. Specifically, a westward wind created conditions that prevented the generation of plasma bubbles. This study offers new insights into how winds during geomagnetic storms affect the ionosphere and helps improve predictions for communication and navigation systems affected by these disruptions. Key Points: Pre‐midnight topside plasma bubbles are inhibited over eastern South America during the recovery phase of a geomagnetic stormZonal wind measurements show evidence of wind‐driven electric fields inhibiting plasma bubble formationAlthough theoretical predictions also anticipate changes in the meridional wind, they are not observed [ABSTRACT FROM AUTHOR]

The 23–24 April 2023 double‐peak (SYM‐H intensities of −179 and −233 nT) intense geomagnetic storm was caused by interplanetary magnetic field southward component Bs associated with an interplanetary fast‐forward shock‐preceded sheath (Bs of 25 nT), followed by a magnetic cloud (MC) (Bs of 33 nT), respectively. These interplanetary structures were led by a coronal mass ejection erupted from the Sun in association with an M1.7 X‐ray flare. At the center of the MC, the plasma density exhibited an order of magnitude decrease, leading to a sub‐Alfvénic solar wind interval for ∼2.1 hr. Ionospheric Joule heating accounted for a significant part (∼81%) of the magnetospheric energy dissipation during the storm main phase. Equal amount of Joule heating in the dayside and nightside ionosphere is consistent with the observed intense and global‐scale DP2 (disturbance polar) currents during the storm main phase. The sub‐Alfvénic solar wind is associated with disappearance of substorms, a sharp decrease in Joule heating dissipation, and reduction in electromagnetic ion cyclotron wave amplitude. The shock/sheath compression of the magnetosphere led to relativistic electron flux losses in the outer radiation belt between L* = 3.5 and 5.5. Relativistic electron flux enhancements were detected in the lower L* ≤ 3.5 region during the storm main and recovery phases. Equatorial ionospheric plasma anomaly structures are found to be modulated by the prompt penetration electric fields. Around the anomaly crests, plasma density at ∼470 km altitude and altitude‐integrated ionospheric total electron content are found to increase by ∼60% and ∼80%, with ∼33% and ∼67% increases in their latitudinal extents compared to their quiet‐time values, respectively. Plain Language Summary: A fast interplanetary coronal mass ejection (ICME) and its upstream sheath caused severe disturbances in the Earth's magnetosphere during 23–24 April 2023. The sheath anti‐sunward of the fast ICME shock was composed of high‐density plasmas and intense magnetic fields. This was followed by a plasma density rarefaction and intense magnetic fields with a field rotation (known as a magnetic cloud). This complex interplanetary structure resulted in a double‐peak geomagnetic storm, and several intense auroral substorms. Solar wind kinetic energy transferred into the magnetosphere during the geomagnetic storm caused large Joule heating in the auroral ionosphere in both dayside and nightside of Earth. Compression of the magnetosphere by the shock/sheath caused losses of relativistic‐energy electrons from the outer radiation belt at the beginning of the magnetospheric event. The equatorial ionospheric anomaly structure, characterized by a low plasma region on the geomagnetic equator and plasma enhancements on both sides (∼±10°) of the equator, was significantly altered during the magnetic storm. In particular, the plasma density crests were more intense and expanded in hemispherical distribution. These variations are attributed to the prompt penetration electric fields to the equatorial ionosphere, which in turn modulated the equatorial ionospheric dynamics. These results should be important for prediction and modeling of geomagnetic storms and their impacts. Key Points: The April 2023 double‐peak geomagnetic storm is a classic event with a sub‐Alfvénic region located in the middle of a magnetic cloudRelativistic electrons displayed classic flux variations and dayside/nightside Joule heating was the dominant storm energy dissipationThe near‐equatorial ionospheric plasma responded to a prompt penetration electric field [ABSTRACT FROM AUTHOR]

As incident solar wind encounters the martian upper atmosphere, it undergoes deflection particularly in the magnetosheath. However, the plasma flow exhibits asymmetrical distribution features within this transition region, which is investigated by employing a three‐dimensional Hall magnetohydrodynamic (MHD) model from an energy transfer perspective in this study. Simulation results reveal that solar wind protons transfer momentum to ionospheric heavy ions through motional electric field in the hemisphere where the motional electric field points outward from the planet. In the opposite hemisphere, solar wind flow tends to be effectively accelerated by ambipolar and Hall electric fields. The distinct dynamics of solar wind protons in both hemispheres result in the asymmetrical deflection. Furthermore, the extent of asymmetry grows as the cross‐flow component of the upstream interplanetary magnetic field increases, but diminishes as the density of the solar wind proton increases, contingent upon the energy effectively acquired from ambipolar and Hall electric fields. Plain Language Summary: Due to the lack of a global intrinsic magnetic field at Mars, the solar wind has a direct interaction with the upper atmosphere of the planet. During this interaction, heavy ions from the martian ionosphere can be accelerated by the motional electric field of the solar wind, resulting in an excess of momentum in the martian system that necessitates the deflection of solar wind protons in the opposite direction to maintain balance. In this study, we utilize a Hall‐MHD model to study the asymmetrical deflection of the solar wind in the martian magnetosheath from an energy transfer perspective. Simulation results indicate that solar wind protons tend to effectively acquire energy from the ambipolar and Hall electric fields in the hemisphere opposite to the direction of the motional electric field and transfer its energy to heavy ions through the motional electric field in the opposite hemisphere, leading to an asymmetrical deflection of the solar wind. Furthermore, the degree of asymmetry is impacted by external solar wind conditions, including the strength of interplanetary magnetic field cross‐flow component and the density of solar wind protons. These findings provide valuable insights into the flow asymmetries that arise during the interaction between Mars and solar wind. Key Points: The multi‐fluid MHD model effectively reproduces the asymmetrical deflection of solar wind flow within the magnetosheathThe asymmetrical deflection of solar wind is a consequence of the discrepancy in energy transfer patterns between the two hemispheresThe impact of the strength of interplanetary magnetic field By and solar wind density on asymmetrical deflection is individually examined [ABSTRACT FROM AUTHOR]

It is commonly believed that because of the direct solar wind interaction with the Martian atmosphere/ionosphere, the planet could have lost a significant part of its atmosphere. Closed field lines of the crustal magnetic field can weaken a transport of the ionospheric ions to the tail. Reconnection of the interplanetary magnetic field lines draping around Mars and the crustal magnetic field can also lead to a presense of sunward fluxes of planetary ions that might affect the total ion loss. The LatHyS (LATMOS Hybrid Simulation) three‐dimensional multispecies hybrid model is used here to characterize sunward fluxes of O+ ions and the magnetic field topology at Mars. It is shown that although reconnection between the interplanetary magnetic field (IMF) and the crustal magnetic fields strongly modifies the field topology, then sunward ion fluxes are rather small and do not significantly change the total ion loss. Plain Language Summary: Although Mars has no a global intrinsic magnetic field and solar wind interacts directly with the planetary atmosphere/ionosphere, the existence of strong but localized crustal magnetic field modifies the field topology around Mars. As a result, the Martian magnetosphere contains elements of the intrinsic and the induced magnetospheres. Reconnection between the interplanetary magnetic field and the crustal magnetic field can generate the plasma flows toward the planet and decrease the ionospheric losses, which is very important for the evolution of the Mars atmosphere/ionosphere. We have performed the numerical simulations of these potential effects and shown that the sunward ion fluxes are significantly less than the losses induced by the solar wind impact on the Martian ionosphere. Key Points: Hybrid simulations show a drastic change of the field topology at altitudes less than ∼1,000 km due to crustal field sourcesAlthough the magnetic field topology is modified, the sunward fluxes do not essentially affect the total ion lossSunward fluxes of oxygen ions in the tail vary between ∼5% and ∼20% compared to the anti‐sunward fluxes [ABSTRACT FROM AUTHOR]

The generation of cosmic ray particles with ultra‐relativistic energies is a crucial issue in astrophysical and space physics. Shocks have been acknowledged as efficient accelerators in the universe which can produce energetic particles through a variety of mechanisms, such as diffusive shock acceleration (DSA), shock surfing acceleration (SSA) and shock drift acceleration (SDA). Using the data set obtained by the Magnetospheric Multiscale mission, we report an unusually sharp enhancement of energetic electron flux in the upstream region of Earth's bow shock, associated with a bipolar variation of the interplanetary magnetic field. To explain these observations, we propose a two‐step acceleration scenario where electrons trapped in a flux rope (FR) first undergo head‐on collisions and are further accelerated by FR contraction as the FR crosses the shock. Such a scenario can well explain the spacecraft observations. This work can improve our understanding of particle acceleration processes at shocks. Plain Language Summary: The cosmic ray comprises ions and electrons with energies up to 1,020 eV and thus its generation mechanism is an important issue. A conventional theory known as diffusive shock acceleration is a promising candidate but it needs seed electrons with sufficient initial energies. How these electrons are generated is still unclear. In this study, we report an unusually sharp enhancement of energetic electron flux with a large variation of magnetic field direction in the upstream region of Earth's bow shock, and propose a two‐step acceleration scenario to explain the spacecraft measurements. Electrons first gain energies from the head‐on collisions with the bow shock, and then bounce between the two ends of a circular magnetic field of shrinkage, analogous to a ball reflecting between two converging walls. This scenario has been mathematically confirmed and shows good agreement with the spacecraft measurements. Key Points: Efficient electron acceleration is observed when a flux rope collides with the Earth's bow shockElectrons trapped in the flux rope are successively accelerated by the head‐on reflection at shock front and the flux rope contractionThis two‐step acceleration scenario is mathematically reproduced and fit the spacecraft observations well [ABSTRACT FROM AUTHOR]

Recent studies have suggested that the interplanetary magnetic field (IMF) By ${B}_{y}$ component modulates particle precipitation during solstices, or periods of high dipole tilt Ψ ${\Psi }$. So far this explicit IMF By ${B}_{y}$‐effect has only been shown in statistical studies. Here we analyzed a sequence of high‐speed stream (HSS) driven events of auroral (<30 ${< } 30$ keV) and medium energy (>30 ${ >} 30$ keV and >100 ${ >} 100$ keV) particle precipitation. We show that when HSSs are comparable in terms of IMF and solar wind parameters, they can lead to systematically stronger particle precipitation in individual events when the signs of By ${B}_{y}$ and Ψ ${\Psi }$ are opposite. We also perform a superposed epoch analysis of 485 HSSs giving further evidence that the By ${B}_{y}$‐effect is especially significant during HSSs. This is likely due to the persistent IMF By ${B}_{y}$ polarity during HSSs. We show evidence that the By ${B}_{y}$ dependence in particle precipitation is caused by a similar By ${B}_{y}$ dependence in substorm occurrence. Plain Language Summary: Intervals of fast solar wind occur the most during the declining phase of the 11‐year solar cycle. Such events are associated with a highly varying north‐south component of the magnetic field of the solar wind, which is known to increase geomagnetic activity. On the contrary to the north‐south directed magnetic field, the east‐west directed field remains very stable during events of fast solar wind. Recent studies have shown that the eastward (westward) magnetic field of the solar wind increases geomagnetic activity in the northern hemispheric winter (summer). We show observations of this effect in geomagnetic activity and particle precipitation from December 2007 to January 2008, when the Earth was hit by two recurring intervals of fast solar wind. We also show statistical results of this effect from intervals of fast solar wind in winter and summer seasons. Key Points: The interplanetary magnetic field (IMF) By ${B}_{y}$ component modulates electron precipitation during high dipole tilt (solstices)The explicit IMF By ${B}_{y}$ dependence of electron precipitation is demonstrated to be strong during high‐speed streamsElectron precipitation is 60%–70% stronger for By ${B}_{y}$ > 0 in northern winter and for By ${B}_{y}$ < 0 in northern summer [ABSTRACT FROM AUTHOR]

The Kelvin-Helmholtz Instability (KHI), arising from velocity shear across the magnetopause, plays a significant role in the viscous-like transfer of mass, momentum, and energy from the shocked solar wind into the magnetosphere. While the KHI leads to growth of surface waves and vortices, suitable detection methods for these applicable to magnetohydrodynamics (MHD) are currently lacking. A novel method is derived based on the well-established A-family of hydrodynamic vortex identification techniques, which define a vortex as a local minimum in an adapted pressure field. The J x B Lorentz force is incorporated into this method by using an effective total pressure in MHD, including both magnetic pressure and a pressure-like part of the magnetic tension derived from a Helmholtz decomposition. The AMHD method is shown to comprise of four physical effects: vortical momentum, density gradients, fluid compressibility, and the rotational part of the magnetic tension. A local three-dimensional MHD simulation representative of near-flank magnetopause conditions (plasma 's 0.5-5 and convective Mach numbers Mf ~ 0.4) under northward interplanetary magnetic field (IMF) is used to validate AMHD. Analysis shows it correlates well with hydrodynamic vortex definitions, though the level of correlation decreases with vortex evolution. Overall, vortical momentum dominates AMHD at all times. During the linear growth phase, density gradients act to oppose vortex formation. By the highly nonlinear stage, the formation of small-scale structures leads to a rising importance of the magnetic tension. Compressibility was found to be insignificant throughout. Finally, a demonstration of this method adapted to tetrahedral spacecraft observations is performed. [ABSTRACT FROM AUTHOR]

This article discusses a study that validates the MAGNetosphere-Ionosphere-Thermosphere (MAGNIT) model against AMPERE measurements of field-aligned currents (FACs) during the "Galaxy 15" space weather event. The study compares the performance of three ionosphere electrodynamic models and finds that MAGNIT exhibits slightly improved predictions compared to other models. The article provides valuable information on auroral precipitation sources and their impact on FACs, which can be used to enhance the model. The study also analyzes various metrics and provides recommendations for optimizing the model's performance. [Extracted from the article]

In this study, the evolutional features and underlying driving mechanisms of the postmidnight‐to‐dawn equatorial plasma bubble (EPB) irregularities during the weak geomagnetic activity period on 13 November 2015 were investigated based on the multiple satellite and ground‐based observations. By using the coherent scatter radar operating at very high frequency at Fuke (19.5°N, 109.1°E, dip latitude 14.4°N), China, it was found that the freshly developed field‐aligned irregularities (FAIs) occurred within the radar's field of view around ∼04:37 LT and sustained for more than 40 min. The remarkable EPB‐related density and total electron content (TEC) depletions measured by the satellite and GNSS receivers were also observed, which indicates the persistence of EPB irregularities until ∼06 LT. The significant elevation of bottomside F‐layer's virtual height obtained by the Digisonde at Fuke as well as the upward vertical F‐layer plasma drifts derived from a nearby Digisonde at Sanya (18.4°N, 109.6°E, dip latitude 13.1°N) both imply the existence of strong eastward perturbation electric fields after local midnight. These findings suggest that the collective effects of eastward overshielding penetration electric field (PEF) resulted from the substorm onset and rapid northward turning of the interplanetary magnetic field (IMF) Bz, surpassed the role of westward undershielding prompt penetration electric field (PPEF) induced by the southward turning of IMF Bz. Thus, the former predominated in modulating the equatorial/low‐latitude zonal electric fields and raised the F‐layer considerably, which consequently boosted the growth of R‐T instability and created the favorable conditions for the postmidnight‐to‐dawn EPBs development. Key Points: Freshly developed field‐aligned irregularities last for 40 min within the radar's field‐of‐view and the equatorial plasma bubble (EPBs)‐related density depletions show the EPBs sustaining until ∼06 LTThe competition process among different perturbation electric fields for triggering the postmidnight‐to‐dawn EPB irregularities is examinedThe eastward overshielding penetration electric field resulted from substorm onset and interplanetary magnetic field Bz northward turning provide favorable conditions for EPB development [ABSTRACT FROM AUTHOR]

This paper describes a catalog of simultaneous observations of the Earth's magnetosheath by ESA's Cluster and NASA's MMS missions. The catalog is built from a visual inspection of summary plots provided by the two missions complemented by an analysis of high‐resolution magnetic field data. The catalog includes 117 events when Cluster 4 and MMS 4 crossed simultaneously the magnetosheath between January–April, 2017–2021. The dynamical and turbulent features of the magnetosheath are strongly influenced by θBn, the angle between the interplanetary magnetic field (IMF) and the shock normal direction. To facilitate such investigations, we also determine the bow shock geometry for each event based on two different approaches: (a) a minimum variance analysis of in‐situ magnetic field measurements, and (b) a geometrical approach which considers a bow shock model parameterized by OMNI data. A description of spacecraft trajectory during each event is also provided. Additional data describe the relative distances between Cluster 4 and MMS 4, a classification of each event as either quasi‐parallel or quasi‐perpendicular, and the distribution of events per magnetospheric flank. The time intervals for the Cluster ‐ MMS conjunctions are included in the catalog, as well as all associated figures and tables discussed in this paper are made available through an independent online data repository, and can be freely downloaded and used by any interested researcher. Key Points: We use in‐situ measurements from Cluster 4 and MMS 4 to build a catalog/database of simultaneous observations of the Earth's magnetosheathEmpirical models and minimum variance analysis of the magnetic field allow for an estimation of the bow‐shock orientation for each eventWe also provide details on the relative spacecraft position and an analysis of the bow‐shock geometry [ABSTRACT FROM AUTHOR]

This study investigates field-aligned currents (FACs) during strong magnetic storms in December 2023, analyzing variations in different local times and in the Northern (NH) and Southern Hemispheres (SH). Peak FAC densities were approximately 7.8 times higher than nominal values, with the most equatorward FACs reaching −52° magnetic latitude (MLat). In the summer hemisphere, the daytime FACs were stronger than the nighttime FACs, with the daytime westward Polar Electrojet (PEJ) surpassing nighttime levels. In the winter hemisphere, the nighttime FACs and westward PEJ were stronger than daytime. Generally, the FACs and westward PEJ were stronger in the SH than in the NH across most local time sectors, attributed to greater solar illumination. The NH pre-midnight currents were stronger than for the SH, indicating enhanced substorm currents during winter nights. The nighttime FACs occurred at lower MLat than daytime, with pre-noon FACs at a higher MLat than post-noon. The NH FACs were positioned more equatorward than their SH counterparts. In the NH, the mean FACs correlated most strongly with the merging electric field (Em) at pre-noon, post-noon, and post-midnight and with the SMU (SuperMAG Electrojet Upper Index) at pre-midnight. In the SH, the mean FACs correlated best with the SMU at pre-midnight/pre-noon, with the SML (SuperMAG Electrojet Lower Index) at post-midnight, and Em at post-noon. The mean MLat of the peak FACs show the strongest correlation with Em across most local times and hemispheres. [ABSTRACT FROM AUTHOR]

Currently, the 25th solar activity peak has commenced, driving frequent geomagnetic storms and causing irregular disturbances in the global ionosphere, leading to the scintillation of Global Positioning System (GPS) signals, consequently decreasing the accuracy of GPS positioning. Analyzing the patterns of global ionospheric scintillation and changes in GPS positioning accuracy caused by geomagnetic storms is crucial to mitigate the adverse effects of GPS positioning. Current research has primarily concentrated on analyzing the effects of geomagnetic storms on ionospheric scintillation disturbances and GPS positioning interference. However, there is a notable gap in studying the holistic impact of coronal mass ejections (CMEs)-driven geomagnetic storms on GPS performance as an integrated event complex. This study investigates the conditions under which a CME drives a severe geomagnetic storm to elucidate the space weather phenomena associated with CME-driven geomagnetic storms. The ionospheric scintillation induced by the geomagnetic storm is analyzed, while we also examine the accuracy variability in kinematic precision point positioning (PPP) and its possible leading reasons. The research findings suggest that factors such as a high-speed full-halo CME, a southward interplanetary magnetic field (IMF) Bz, and high-speed solar wind contribute to the onset of this geomagnetic storm. Ionospheric scintillation and the decrease in positioning accuracy in low-latitude regions are less pronounced compared to mid- and high-latitude areas. Geomagnetic-storm-induced scintillation increases cycle slips, leading to a decrease in PPP accuracy. Even in the cases where geomagnetic storms do not induce ionospheric scintillation, positioning accuracy can still be affected by cycle slips, deterioration of the precision of the GPS measurements, data outages, and the decrease in the number of available satellites. [ABSTRACT FROM AUTHOR]

In this study, the thermospheric mass density (TMD) features observed by the CHAllenging Minisatellite Payload between 2002 and 2010 were extracted using deep learning (DL) technology; the TMD features were then mapped and modeled with the Interplanetary environment information (IEI), solar radiation, and geomagnetic indices. The DL model was used to simulate the TMD features during Day of Year (DOY) 222–241 in 2014, a period that experienced complex solar‐terrestrial environmental variations. We explore the TMD features under different solar‐terrestrial environmental conditions and discuss the effects of various inputs by comparing the DL simulation results with satellite observations from Gravity Recovery and Climate Experiment‐A and Swarm‐A, as well as the simulation results from Jacchia‐Bowman 2008, Naval Research Laboratory Mass Spectrometer Incoherent Scatter radar model 2.1, and Drag Temperature Model 2013. These results show that the DL model can better capture the TMD features after adding IEI. Part of these TMD features, including the high‐latitude TMD enhancement during the space hurricane event (DOY 232, 2014) and global TMD variations under complex solar‐terrestrial environmental disturbances (DOY 222–225, 2014), cannot be well described by the geomagnetic indices. The DL model indicates that the east‐west component of the interplanetary magnetic field (IMF By) has a great impact on TMD variations, and its modulation is different from the typical energy injection process during storms. Our results emphasize the crucial influence of IEI on TMD under both geomagnetic disturbances and quiet conditions. Plain Language Summary: In our study, we examined the variabilities of Earth's upper atmospheric density (thermospheric mass density, TMD), and how these variabilities relate to space environment conditions. This is crucial for the aerospace industry and space physics research. We used deep learning (DL) to model TMD variations and simulate a period of time involving complex space environmental disturbances, including geomagnetic storms, substorm, and space hurricane. By comparing the differences in input and TMD features between the DL model, traditional empirical models, and observations, our results show that the interplanetary environmental information (IEI) aids in recognizing and reconstructing TMD variations. Models incorporating IEI more accurately describe TMD features than traditional empirical models do. For example, the TMD increases at high latitudes during space hurricane event and global variations during complex space environmental disturbances. This study advances our understanding of the space environment's impact on TMD variations and supports future modeling efforts. Key Points: The thermospheric mass density (TMD) features under various solar‐terrestrial conditions are investigated by observations and simulationsInterplanetary environment information (IEI) offers unique insights beyond geomagnetic indices for understanding and modeling TMD featuresThe influence of IEI on TMD need be considered during both geomagnetic disturbances and quiet conditions [ABSTRACT FROM AUTHOR]

This paper investigates time‐lag effects of ionospheric response to two severe geomagnetic storms (Kp = 8) on the degradation of kinematic precise point positioning (PPP) solutions, utilizing over 5500 Global Navigation Satellite Systems (GNSS) stations distributed worldwide. Focusing on these two severe geomagnetic storms that occurred during solar cycle 24, the study employs an open‐source positioning software package, namely RTKLIB, to derive the PPP solutions. The findings reveal significant variations in time lags across different magnetic latitudes. These variations are driven by ionospheric responses to a southward interplanetary magnetic field and subsequent decreases in the SMY‐H index during the 2015 St. Patrick's Day Storm and the 2017 September 7–8 Storm. Specifically, at high latitudes, PPP degradation primarily manifests during the main phase of the storm, resulting in delays spanning from several minutes to 1–2 hr after the sudden onset of the storm. In contrast, mid‐ and low latitudes exhibit a wider range of delays extending up to tens of hours. Notably, rapid positioning degradation is observed predominantly at the magnetic local time noon and midnight sectors. The study discusses these time lag effects concerning the intensity of various ionospheric disturbances triggered by the interactions among the solar wind, magnetosphere, and ionosphere during geomagnetic storms. The insights obtained from this research have the potential to be integrated into physics‐based and machine‐learning models to enhance forecasting capabilities of space weather impacts. Plain Language Summary: This paper presents space weather impact on Global Navigation Satellite Systems positioning solutions. Specifically, it examines the time‐lag effects of the ionospheric response to severe geomagnetic storms. The study finds that the time it takes the positioning system to degrade varies depending on the device latitude. At high latitudes, the degradation happens quickly, within minutes to an hour after the storm starts. At mid‐ and low latitudes, the degradation takes longer, sometimes up to tens of hours after the storm onset. The differences in the time lag are related to how the ionosphere reacts to changes in the Earth's magnetic fields during these storms. This study is significant because it quantifies the time difference between the start of a storm and the degradation in the positioning system. The information gained from this research will help improve forecasting space weather impacts. Key Points: Initial attempt to quantify the time lags between the sudden onset of a geomagnetic storm and the degradation in precise point positioning on a global scaleTime lags in high latitudes typically vary from a few minutes to less than 2 hrMiddle and low latitudes responses show a wider range of time lags of up to several tens of hours [ABSTRACT FROM AUTHOR]

We introduce a new multivariate data set that utilizes multiple spacecraft collecting in‐situ and remote sensing heliospheric measurements shown to be linked to physical processes responsible for generating solar energetic particles (SEPs). Using the Geostationary Operational Environmental Satellites (GOES) flare event list from Solar Cycle (SC) 23 and part of SC 24 (1998–2013), we identify 252 solar events (>C‐class flares) that produce SEPs and 17,542 events that do not. For each identified event, we acquire the local plasma properties at 1 au, such as energetic proton and electron data, upstream solar wind conditions, and the interplanetary magnetic field vector quantities using various instruments onboard GOES and the Advanced Composition Explorer spacecraft. We also collect remote sensing data from instruments onboard the Solar Dynamic Observatory, Solar and Heliospheric Observatory, and the Wind solar radio instrument WAVES. The data set is designed to allow for variations of the inputs and feature sets for machine learning (ML) in heliophysics and has a specific purpose for forecasting the occurrence of SEP events and their subsequent properties. This paper describes a data set created from multiple publicly available observation sources that is validated, cleaned, and carefully curated for our ML pipeline. The data set has been used to drive the newly‐developed Multivariate Ensemble of Models for Probabilistic Forecast of SEPs (MEMPSEP; see MEMPSEP‐I (Chatterjee et al., 2024, https://doi.org/10.1029/2023SW003568) and MEMPSEP‐II (Dayeh et al., 2024, https://doi.org/10.1029/2023SW003697) for accompanying papers). Plain Language Summary: We present a new data set that uses observations from multiple spacecraft observing the Sun and the interplanetary space around it. This data is connected to the processes that create solar energetic particles (SEPs). SEP events pose threats to both astronauts and assets in space. The data set contains 252 solar flare events that caused SEPs and 17,542 that do not. For each event, we gather information about the local space environment around the sun, such as energetic protons and electrons, the conditions of the solar wind, the magnetic field, and remote solar imaging data. We use instruments from NOAA's Geostationary Operational Environmental Satellites (GOES) and the Advanced Composition Explorer spacecraft, as well as data from the Solar Dynamic Observatory, the Solar and Heliospheric Observatory, and the Wind solar radio instrument WAVES. This data set is designed to be used in machine learning (ML), with a focus on predicting the occurrence and properties of SEP events. We detail each observation obtained from publicly available sources, and the data treatment processes used to validate the reliability and usefulness for ML applications. Key Points: Machine learning oriented data set for predicting the occurance and properties of solar energetic particle eventsMultivariate remote sensing and in‐situ observationsContinuous data set spanning several decades [ABSTRACT FROM AUTHOR]

During magnetospheric substorms, plasma from magnetic reconnection in the magnetotail is thought to reach the inner magnetosphere and form a partial ring current. We simulate this process using a fully kinetic 3D particle‐in‐cell (PIC) numerical code along with a global magnetohydrodynamics (MHD) model. The PIC simulation extends from the solar wind outside the bow shock to beyond the reconnection region in the tail, while the MHD code extends much further and is run for nominal solar wind parameters and a southward interplanetary magnetic field. By the end of the PIC calculation, ions and electrons from the tail reconnection reach the inner magnetosphere and form a partial ring current and diamagnetic current. The primary source of particles to the inner magnetosphere is bursty bulk flows (BBFs) that originate from a complex pattern of reconnection in the near‐Earth magnetotail at xGSM=−18RE ${x}_{\text{GSM}}=-18{R}_{\mathrm{E}}$ to −30RE ${-}30{R}_{\mathrm{E}}$. Most ion acceleration occurs in this region, gaining from 10 to 50 keV as they traverse the sites of active reconnection. Electrons jet away from the reconnection region much faster than the ions, setting up an ambipolar electric field allowing the ions to catch up after approximately 10 ion inertial lengths. The initial energy flux in the BBFs is mainly kinetic energy flux from the ions, but as they move earthward, the energy flux changes to enthalpy flux at the ring current. The power delivered from the tail reconnection in the simulation to the inner magnetosphere is >2×1011 ${ >} 2\times 1{0}^{11}$ W, which is consistent with observations. Plain Language Summary: During intervals of increased solar activity, the magnetic field in Earth's stretched night‐side tail undergoes intense reconfiguration that can energize particles. This process is called magnetic reconnection. Ions and electrons from reconnection can reach the inner magnetosphere. In this paper, we simulate this process using a novel model that includes Earth's global magnetic field configuration and self‐consistently models particle physics for both electrons and ions. We find that the particles are accelerated significantly near the sites of magnetic field reconfiguration with ions gaining 10 s of keV energy. As they propagate earthward, they end up contributing energetically to the formation of a ring current system partially encircling Earth. Key Points: Ions and electrons accelerated by 10–50 keV near the magnetotail reconnection can reach the inner magnetosphereA partial ring current is formed during the simulation, with highest energy flux between midnight and duskThe ion and electron energy fluxes are mostly kinetic in the reconnection region but change to enthalpy flux earthward [ABSTRACT FROM AUTHOR]

To better understand how sharp changes in the solar wind and interplanetary magnetic field conditions affect the ionosphere outflows at high latitudes, we analyze an event observed on 17 July 2002 showing suprathermal (tens to hundreds of eV) outflowing H+ ions in the lobe driven by the impact of an interplanetary (IP) shock. A spacecraft in the lobe at altitudes of ∼6.5 RE first observed enhanced downward DC Poynting fluxes ∼2 min after the shock impact and then, another 8 min later, the appearance of suprathermal outflowing H+ ions as ion beams and ion conics. The increasing downward DC Poynting fluxes and the increasing outflowing H+ fluxes that appeared later were highly correlated because they shared a similar increasing trend with a time scale of ∼5 min. To explain such time delay and correlation, we conclude that a plausible scenario was that the enhanced DC Poynting fluxes reached down to lower altitudes, drove processes to accelerate the pre‐existing polar wind ions to ion beams and ion conics, and then these newly generated suprathermal ions flowed upward to the spacecraft altitudes. This event indicates that an IP shock can drive a significant amount of suprathermal H+ outflows from the polar cap. Key Points: Cluster observed suprathermal outflowing H+ ion beams and ion conics in the lobe after the impact of an interplanetary (IP) shockThe outflowing H+ ions appeared ∼10 min after the shock impact and ∼8 min after enhanced downward DC Poynting fluxesThe suprathermal outflowing H+ ions were likely pre‐existing thermal polar wind being accelerated caused by the enhanced Poynting fluxes [ABSTRACT FROM AUTHOR]

Utilizing the 8.5‐year Venus Express observations, we investigate the effects of solar wind magnetosonic Mach number MMS $\left({M}_{MS}\right)$, solar extreme ultraviolet (EUV) radiation, solar wind dynamic pressure Pd $\left({P}_{d}\right)$ and interplanetary magnetic field (IMF) on the shape of the Venusian bow shock. Our statistical analysis yields several findings: (a) The spatial scale of the Venusian bow shock varies in a nonlinear manner with MMS ${M}_{MS}$ and shows a linear correlation with the EUV flux. (b) After the variance of the bow shock size caused by different MMS ${M}_{MS}$ and EUV are considered, the bow shock size shows no apparent correlation with the IMF intensity, IMF cone angle and solar wind dynamic pressure. (c) The angle between the IMF and the shock normal θBn $\left({\theta }_{Bn}\right)$ emerges as a significant factor shaping the bow shock's local distance. A two‐parameter (MMS ${M}_{MS}$ and EUV) dynamic bow shock model is consequently constructed. This dynamic model not only elucidates the typical behavior of the bow shock under normal solar wind conditions but also unveils the anomalously distant bow shock location characterized by extremely low MMS ${M}_{MS}$. Key Points: An emprical magnetosonic Mach number‐ and EUV‐dependent model is constructed for the shape of the Venusian bow shockThe effect of interplanetary magnetic field (IMF) intensity on the bow shock location is linked to its correlation with magnetosonic Mach numberThe angle between the IMF and the shock normal plays a significant role in influencing the distance of the bow shock [ABSTRACT FROM AUTHOR]

Kelvin Helmholtz Instabilities (KHI) result from interactions between the shocked solar wind and the Earth's magnetosphere. These are formed due to the velocity shear between the plasma in the magnetosphere and magnetosheath. The role of KHI in bringing in the shocked solar wind into the terrestrial magnetosphere has been studied extensively using MHD, Hall‐MHD, hybrid and PIC simulations. Such simulations oftentimes make simplifying assumptions of the boundary layer in the magnetopause. To experimentally study the effects of KHI on the boundary layer and its effectiveness in bringing in solar wind, we analyze 43 KHI events. All these events have quasi‐constant IMF orientation during its interval, thereby mitigating the effects of variation of IMF in the ongoing transient magnetopause process. In this statistical study of KHIs, we demonstrate that there is a preexisting boundary layer before KHIs begin to develop. As KHI develops to its non‐linear state, the ions in the magnetosphere, magnetopause, and magnetosheath are mixed, which is demonstrated using the alpha‐to‐proton density ratio. As a result of this mixing, the well‐defined preexisting boundary layer is replaced by a much more uniformly mixed boundary layer. Plain Language Summary: Kelvin‐Helmholtz Instabilities (KHI) occur due to differences in plasma velocity on either side of the magnetopause, the boundary between Earth's magnetic field and the solar wind. These instabilities can allow solar wind to enter Earth's magnetosphere. To understand KHI better, we studied 43 events where the interplanetary magnetic field (IMF) was steady, reducing its influence on the results. Our findings indicate that a boundary layer exists before KHI begins. As KHI develops, it mixes particles from Earth's magnetosphere with those from the solar wind, creating a more uniform boundary layer. We can observe this mixing by tracking the ratio of the number density of doubly charged Helium ions particles and protons. Key Points: 43 K Helmholtz Instability (KHI) events have been analyzed under quasi‐constant IMF conditionsThe non‐linear KHI events show evidence for plasma mixing, seen as a smooth transition in the alpha‐to‐proton ratio in the boundary layerWe propose using Alpha‐To‐Proton density ratio as a diagnostic tool to identify the stage of KHI development [ABSTRACT FROM AUTHOR]

We study the dynamic evolution of dayside magnetopause reconnection locations and their dependence on the interplanetary magnetic field (IMF) cone angle via 3‐D global‐scale hybrid simulations. Cases with finite IMF Bx and Bz but IMF By = 0 are investigated. It is shown that the dayside magnetopause reconnection is unsteady under quasi‐steady solar wind conditions. The reconnection lines during the dynamic evolution are not always parallel to the equatorial plane even under purely southward IMF conditions. Magnetopause reconnection locations can be affected by the generation, coalescence, and transport of flux ropes (FRs), reconnection inside the FRs, and the magnetosheath flow. In the presence of an IMF component Bx, the magnetopause reconnection initially occurs in high‐latitude regions downstream of the quasi‐perpendicular bow shock, followed by the generation of multiple reconnection regions. In the later stages of the simulation, a dominant reconnection region is present in low‐latitude regions, which can also affect reconnection in other regions. The global distribution of reconnection lines under a finite IMF Bx is found to not be limited to the region with maximum magnetic shear angle. Plain Language Summary: The channel of solar wind energy transfer into the magnetosphere is widely believed to be controlled by magnetic reconnection at the dayside magnetopause. Understanding the location of dayside magnetopause reconnection is crucial to comprehending the energy coupling process between the solar wind and the magnetosphere. Magnetopause reconnection has been intensively investigated by numerical simulations and space observations. Nevertheless, the locations and dynamic evolution of reconnection sites in the 3‐D magnetopause reconnection under different interplanetary magnetic field (IMF) conditions are barely scrutinized. In this paper, we investigate the effects of IMF Bx on the motion of magnetopause reconnection locations by using 3‐D global hybrid simulations under a southward IMF Bz. We find that the reconnection is highly variable due to local magnetopause processes associated with the generation, coalescence, and transport of flux ropes (FRs), as well as reconnection inside the FRs. Under southward IMF conditions with IMF Bx, the magnetopause reconnection initially occurs downstream of the quasi‐perpendicular bow shock but eventually dominates in low‐latitude regions, including the magnetopause downstream of the quasi‐parallel bow shock. Key Points: Dayside magnetopause reconnection is highly variable but the reconnection locations eventually maintain quasi‐steady in the low latitudeIn the presence of interplanetary magnetic field Bx, high‐latitude dayside reconnection can be inhibited by reconnection near the equator and magnetosheath flowVariations of reconnection locations are also controlled by the generation, coalescence, and transport of flux ropes (FRs), and reconnection inside FRs [ABSTRACT FROM AUTHOR]

Magnetospheric convection is a fundamental process in the coupling of the solar wind, magnetosphere, and ionosphere. Recent studies have shown that dayside magnetopause reconnection drives magnetospheric convection, progressing from the dayside to the nightside within approximately 10–20 min in response to southward turning of the interplanetary magnetic field. In this study, we use global magnetohydrodynamic (MHD) simulations to investigate the influence of ionospheric conductance on dayside‐driven convection. We conduct three simulation runs: two with normal ionospheric conductance and one with nearly infinite conductance. The temporal and spatial pattern of magnetospheric convection largely remain consistent across all three simulation runs. Comparing the results, we observe a reduction of 20% in magnetospheric convection and a 30% increase of ionospheric Region 1 field‐aligned current (FAC) and Pedersen current in the run with nearly infinite conductance, compared to the normal conductance model. The results indicate that ionospheric conductance does not affect the response time of enhanced magnetospheric convection to the solar wind. We suggest that the 10–20 min timescale for establishing magnetospheric convection corresponds to the anti‐sunward drag of reconnected magnetic field lines from the sub‐solar point to the flank magnetopause. In cases of larger ionospheric conductance, the ionosphere footprints of dragged field lines become more stationary, potentially resulting in larger Region 1 FAC and ionosphere Pedersen current. A larger Pedersen current is associated with stronger sunward J × B force in the ionosphere, which corresponds to a stronger anti‐sunward force in the magnetosphere, thereby reducing sunward convection of closed field lines. Key Points: An approximately infinite ionospheric conductance reduces the magnetospheric convection on the equatorial plane by ∼20%The ionospheric FAC and Pedersen current increase ∼30% as the magnetospheric convection is reducedThe response time of the enhanced magnetospheric convection to solar wind is not impacted by the ionosphere conductance [ABSTRACT FROM AUTHOR]

The interplanetary magnetic field (IMF) north‐south component, Bz, plays a crucial role in the interaction between the solar wind and the Earth's magnetosphere. We analyze 98 intervals in which Bz changed from >3 nT to <−3 nT in 5 min and for which these rapid southward turnings (STs) were surrounded by consistently northward or southward IMF. We separate out events in proximity of interplanetary coronal mass ejections and corotating interaction regions. We find that IMF magnitude, solar wind dynamic pressure and proton density (but also flow speed in ICME‐related events) near the turnings are enhanced above their medians. We analyze the maximum responses of the SML, SMU, SYM‐H, and PCN magnetospheric indices and their timescales, along with the occurrence of geomagnetic phenomena. We find that most STs were followed by either substorms (60.20%) or enhanced convection (37.76%). While SML has similar median minima (∼−460 nT) and timescales (∼56 min) for substorm and convection events, SMU has noticeable differences. STs were followed by geomagnetic storms (SYM‐H ≤ −50 nT) in 46.94% of events within 12 hr, with more storms following ICME‐related turnings. PCN has peaks (median 3.8 mV/m) around 30 min after the turning, and larger ones (median 4.9 mV/m) later. Stronger solar wind driving and magnetospheric responses are observed for ICME‐related events. The correlation between the geomagnetic and solar wind parameters around STs reveals a more direct link between solar wind driving and geomagnetic response for STs than at other times. Key Points: Linear correlation between the geomagnetic response and the preceding solar wind conditions is generally enhanced after southward turnings (STs)The PCN index shows an almost immediate response to STs, reaching a peak with a median timescale of 30 min46.9% of STs were followed by geomagnetic storms (SYM‐H ≤ −50 nT), 60.2% by substorms, and 37.8% by enhanced convection [ABSTRACT FROM AUTHOR]

In this study, we investigate the impacts of the 17 March 2013 strong geomagnetic storm on the wholly coupled Solar Wind‐Magnetosphere‐Ionosphere‐Thermosphere system‐of‐systems. Obtained from multipoint observations, our new results show (1) the solar‐wind Alfven waves propagating antisunward in the sheath region and (2) oscillating solar wind interplanetary magnetic field (IMF) and electric (E) field (IEF EY) that powered (3) rigorous dayside and nightside flux transfer events (FTEs) when (4) the nightside‐reconnection‐related short circuiting led to fast‐time Subauroral Ion Drifts (SAID) and Subauroral Polarization Streams (SAPS) E field development across the inner‐magnetosphere plasmapause where the solar‐wind Alfven waves (4) transitioned into kinetic Alfven waves (5) fueling the hot zone. Also, the antisunward solar‐wind Alfven waves (6) drove enhanced large‐scale region‐1 field‐aligned currents creating (7) undershielding conditions (8) allowing the dawn‐to‐dusk convection E field's earthward penetration, and (9) generated increased solar‐wind kinetic energy, which became deposited (10) to the ionosphere increasing the ionospheric electron temperature (by the downward flowing suprathermal electron fluxes) and (11) to the thermosphere oscillating the neutral winds and increasing the neutral temperature, and finally leading to (12) the development of bright stable auroral red (SAR) arcs in (13) the enhanced SAID/SAPS flow channels (FCs) developed during FTEs, (14) demonstrated with FC‐2 and FC‐3 events, in the enhanced polar convection that (15) the Rice Convection Model could reproduce. Finally, we conclude the antisunward‐propagating large‐amplitude solar‐wind Alfven waves' ultimate significant role in creating the favorable conditions for the various phenomena documented with the new observational results (1–14). Plain Language Summary: We investigate the wholly coupled Solar Wind‐Magnetosphere‐Ionosphere‐Thermosphere (SW‐M‐I‐T) system‐of‐systems operational during the 17 March 2013 strong geomagnetic storm. Results show the development of two significant phenomena in the coupled SW‐M system: (a) the region 1 field‐aligned currents and (b) the antisunward solar‐wind Alfven waves. While (a) created undershielding conditions allowing the dawn‐to‐dusk electric field (Edd) earthward propagation, (b) drove (B field, E field, wind) oscillations and generated kinetic energy (up to ∼400 TW) that became deposited (up to ∼5 TW) into the magnetosphere efficiently (up to ∼2.5%). In the coupled M‐I system, the kinetic energy drove reconnection events while the Edd convected the plasma in a two‐cell pattern. During nightside reconnection, the earthward injected ring current (RC) protons led to the development of the hot zone and conjugate large‐scale E fields near/across the plasmapause, while the downward heat flux channeled into the ionosphere elevated the electron temperature (Te). In the coupled I‐T system, the elevated Te increased the thermospheric neutral temperature (Tn) and both (Te and Tn) ignited the stable auroral red arc while the thermospheric neutral winds became oscillatory because of the antisunward solar‐wind Alfven waves that acted as the ultimate driver of the wholly coupled SW‐M‐I‐T system‐of‐systems operational. Key Points: Solar‐wind Alfven waves led to SAID/SAPS development via reconnection and transitioned into kinetic Alfven waves fueling the hot zoneEnhanced R1 FACs led to undershielding permitting the dawn‐to‐dusk convection E field's earthward penetration (to L ≈ 6 RE) on the nightsideOscillating thermospheric neutral winds and neutral temperature increase led to the development of bright SAR arcs [ABSTRACT FROM AUTHOR]

After leaving the Sun’s corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. Alfvén waves are perturbations of the interplanetary magnetic field that transport energy. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecraft to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the plasma between the outer edge of the corona and near the orbit of Venus, along with the presence of large-amplitude Alfvén waves. We calculate that the damping and mechanical work performed by the Alfvén waves are sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere. [ABSTRACT FROM AUTHOR]

The properties of the magnetosheath are of pivotal importance in determining the coupling between the magnetosphere and interplanetary medium. In particular, the magnetic flux pileup and plasma depletion layer (PDL) modify the boundary conditions of magnetopause reconnection. However, the spatial distribution of the magnetic field strength and plasma density in the magnetosheath and their functional dependence on the interplanetary magnetic field (IMF) orientation remain poorly understood. This study characterizes these aspects in detail through the statistical processing of decades of data from Cluster, Double Star, THEMIS, and Magnetospheric Multiscale (MMS) missions. The first part of this study focuses on the poorly known variations across the magnetosheath, from the shock to the magnetopause. The magnetic pileup and PDL are significantly correlated, with a strong dependence on the IMF cone angle. Their dependence on the IMF clock angle is found only near the magnetopause, consistent with the expected effect of magnetic reconnection. The second part of this study examines the asymmetry in the magnetic field amplitude and density between the quasi-parallel and quasi-perpendicular sides of the equatorial magnetosheath. These asymmetries are characterized for different relative distances to the magnetopause and bow shock boundaries and for different IMF orientation. The magnetic field amplitude, observed to be higher on the quasi-perpendicular side of the magnetosheath, becomes more symmetric as it approaches the magnetopause. The quasi-parallel magnetosheath exhibits a higher plasma density near the magnetopause. However, this asymmetry reverses at approximately the mid-magnetosheath with a decreasing IMF cone angle. [ABSTRACT FROM AUTHOR]

Disturbances in the Interplanetary Magnetic Field (IMF) and solar conditions can affect the geomagnetic field measurements. In the current study, the influence of IMF and solar fluctuations on the nighttime Pc3-5 and Pi2 pulsations at low latitudes is investigated. Geomagnetic data recorded by the Egyptian geomagnetic observatories are used to examine the occurrence of nighttime pulsation events in Egypt. The corresponding daytime data from the Honolulu (HON) INTERMAGNET observatory were used for comparison between nighttime and daytime pulsation activity aiming for a better understanding of their sources. Two pulsation activities occurred on 7 and 27 February 2014 under different IMF and solar conditions were examined. Results of data analysis indicate that geomagnetic field fluctuations (Pc3-5 and Pi2 pulsations) are affected by changes in the IMF and solar conditions. The occurrence of space weather events such as geomagnetic storms and Coronal Mass Ejections (CMEs) can significantly affect the coherence and correlations between the pulsation wave-packets observed at nighttime and daytime suggesting different generation mechanisms for each pulsation event. [ABSTRACT FROM AUTHOR]

The occurrence of space weather events, notably geomagnetic storms driven by various solar wind structures, can significantly alter Earth's electromagnetic environment. In this study, we examined the interplanetary origins and statistical distribution of 384 geomagnetic storms ( D s t m i n   ≤ −50 nT) that occurred from September 1996 to December 2023. We statistically analyzed the correlations between storm intensity and solar wind parameters (SWPs) across different subsets. The results indicate that (1) the solar activity level, indicated by the sunspot number (SSN), and the number of geomagnetic storms during the first four years of the 25th solar cycle were intermediate, compared to the first four years of the 23rd and 24th solar cycles. Specifically, ICME-related structures caused 80% of the strong storms ( D s t m i n   ≤ −100 nT) and 34% of the moderate storms (−100 nT < D s t m i n   ≤ −50 nT) from 2020 to 2023. (2) The storm intensity correlated with the peak and/or time-integral values of the southward interplanetary magnetic field (IMF B s ), the dawn–dusk electric field ( E y ), the Akasofu's function (ε), and dynamic pressure ( P s w ) to varying extents. Strong storms exhibited higher correlation levels than moderate ones and ICME-related storms showed larger correlation levels compared to those driven by other sources. (3) Compared with the storms from 1996-09 to 2000-08, the storms that occurred from 2020 to 2023 had lower correlations with the peak values of the IMF B s and E y but higher correlations with the peak value of ε and the time-integral values of the IMF B s , E y , P s w , and ε. (4) Among the 174 events that featured continuous southward IMF during the storm's main phase, the duration of southward IMF during about 66.7% of moderate storms and 51.5% of strong storms were less than 13 h. Continuous southward IMF resulted in more direct and efficient energy coupling, enhancing the correlation between the peak values of SWPs and storm intensity but weakening the relationships with the time-integral values of SWPs. Notably, when the southward IMF persisted for a longer duration (e.g., ∆t > 13 h), the continuous energy input further enhanced correlations with both peak and integral values of SWPs, leading to stronger overall correlations with storm intensity. This analysis sheds light on the intricate relationships between geomagnetic storms and their solar wind drivers, emphasizing the significant influence of ICME-related structures and the duration of southward IMF on storm intensity. [ABSTRACT FROM AUTHOR]

The long‐standing "energy crisis" at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin‐Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar‐wind‐magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune. Plain Language Summary: The upper atmospheres of Jupiter, Saturn, Uranus, and Neptune are all hotter than would be predicted by their exposure to sunlight alone. The space plasma environment around each planet provides an additional reservoir of energy that can be used to provide this heating. Here we quantify the average energy input to each planetary system due to variation of the photons and plasmas emitted from the Sun. We find that the interaction between a planetary magnetic field and the solar interplanetary magnetic field provides a strong source of external energy at each of the planets, on average significantly more than that of light from the Sun. Key Points: Solar wind‐magnetospheric‐coupling provides higher energy input than solar extreme ultraviolet at the giant planetsSolar activity drives solar‐wind‐magnetospheric coupling much more strongly than planetary seasonThe solar wind may drive the energy input to the upper atmospheres at Uranus and Neptune [ABSTRACT FROM AUTHOR]

Since solar cycle 16, the heliospheric current sheet (HCS) has been found to be shifted southward during the late declining to minimum phase. However, this trend is broken at the end of solar cycle 24. In this paper, we analyse the shift of the HCS by using information obtained from coronal model and in situ data provided by the near-Earth OMNI data base and the Parker Solar Probe (PSP). Coronal potential field source surface modelling results show that the northward shift is established at the beginning of 2018 and remains stable for about 2 yr. Interplanetary magnetic field data obtained from and within 1 au also support the northward shift, as the southern polarity T appears more frequently than the northern polarity A between 2018 and 2020. Both model results and in situ observation obtained by PSP imply that the HCS shift is established in the corona, and then propagates into the heliosphere. The quadrupole term still has a significant influence on the formation of the HCS shift. [ABSTRACT FROM AUTHOR]

On 21 April 2023, a significant M1.7 solar flare erupted from Active Region 13283, accompanied by a filament eruption and a full-halo Coronal Mass Ejection, which reached Earth on 23 April, triggering a severe geomagnetic storm, with Kp reaching 8 (G4) and Dst plummeting to −212 nT together with a sharply distinguished long-lasting negative double-dip behavior of the z -component of the interplanetary magnetic field. This event led to remarkable auroral displays, even at mid-latitudes in Europe. The flare-induced filament eruption caused distinct intensity dimming in the solar corona, observed in specific EUV wavelengths. We observed the dimming region growing at its fastest rate before the flare reached its peak of intensity. Notably, the proximity of the flare to a large southern coronal hole influenced the expansion and propagation of the coronal mass ejection toward Earth, probably impacting the solar wind speed and density. Additionally, we observed a sudden expansion of the coronal hole during the flare, leading us to speculating that the adjacent flare may have further stimulated the flow of solar-wind particles along the open magnetic-field lines. In accordance with the severe Dst-index disturbance, we also report changes in the potential of the pipeline of an Italian energy infrastructure company with respect to the surrounding soil as well as double-dip variation in the H-component of the terrestial magnetic field observed locally (reminiscent to what reported in Dst-index and IMF Bz) temporal profiles, confirming the effects of the geomagnetic storm at Italy mid-latitudes. Several solar radio events have been observed too. Therefore this study provides insights into the dynamic solar phenomena and their potential geomagnetic implications. [ABSTRACT FROM AUTHOR]

The article "Ionosphere Monitoring with Remote Sensing Vol II." provides an overview of the importance of studying the Earth's ionosphere and its influence on space weather. It discusses the use of remote sensing and in situ instruments to investigate ionospheric features and anomalies. The article presents original research papers that contribute to the understanding of the ionosphere and its relevance for signal transmission and space weather studies. It also explores the use of artificial intelligence technology in ionospheric prediction models and the study of ionospheric anomalies associated with natural phenomena. The research findings highlight the complex nature of the ionosphere and its impact on communication and navigation systems. [Extracted from the article]

The unusual daytime F-region Field-Aligned Irregularities (FAIs) were observed by the HCOPAR and the satellites at low latitudes on 13 June 2022. These irregularities survived from night-time to the following afternoon at 15:00 LT. During daytime, they appeared as fossil structures with low Doppler velocities and narrow spectral widths. These characteristics indicated that they drifted along the magnetic field lines without apparent zonal velocity to low latitudes. Combining the observations of the ICON satellite and the Hainan Digisonde, we derived the movement trails of these daytime irregularities. We attributed their generation to the rapid ascent of the F-layer due to the fluctuation of IMF Bz during the quiet geomagnetic conditions. Subsequently, the influence of the substorm on the low-latitude ionosphere was investigated and simulated. The substorm caused the intense Joule heating that enhanced the southward neutral winds, carrying the neutral compositional disturbances to low latitudes and resulting in a negative storm effect in Southeast Asia. The negative storm formed a low-density circumstance and slowed the dissipation of the daytime FAIs. These results may provide new insights into the generation of post-midnight irregularities and their relationship with daytime fossil structures. [ABSTRACT FROM AUTHOR]

The heliospheric current sheet (HCS) serves as the boundary that separates two sectors in which the interplanetary magnetic field lines diverge in opposite directions. In this study, we conducted a statistical analysis of 216 HCS events, utilizing data from the Wind spacecraft to examine the impact of stream interaction regions (SIRs) on the HCSs. Our findings revealed that out of all the HCS events, 153 (70.8%) were succeeded by a SIR within 36 h. Conversely, 63 HCS events (29.2%) were not followed by any SIR. The occurrence of HCSs accompanied by SIRs displayed a rough anti-correlation with solar sunspots. The statistical results further indicated that the presence of a SIR exerts some influence on the preceding HCS. Specifically, the thickness of the HCS is significantly reduced by the trailing SIR, and the subsequent SIR can cause the leading HCS to stand more vertically to the ecliptic plane and more aligned with the Sun–Earth line (a smaller angle between the normal of the HCS and the Earth's dawn–dusk line in the ecliptic plane). [ABSTRACT FROM AUTHOR]

Regression models (LEEMYR: Low Energy Electron MLT geosYnchronous orbit Regression) predict hourly 4.1–30 keV electron flux at geostationary orbit (GOES‐16) using solar wind, IMF, and geomagnetic index parameters. Multiplicative interaction and polynomial terms describe synergistic and nonlinear effects. We reduce predictors to an optimal set using stepwise regression, resulting in models with validation comparable to a neural network. Models predict 1, 3, 6, 12, and 24 hr into the future. Validation correlations are as high as 0.78 (4.1 and 11 keV, 1 hr prediction) and Heidke Skill scores (HSS) up to 0.66. A 3 hr ahead prediction is more practical, with slightly lower validation correlation (0.75) and HSS (0.61). The addition of location (MLT: magnetic local time) as a covariate, including multiplicative interaction terms, accounts for location‐dependent flux differences and variation of parameter influence, and allows prediction over the full orbit. Adding a substorm index (SME) provides minimal increase in validation correlation (0.81) showing that other parameters are good proxies for an unavailable real time substorm index. Prediction intervals on individual values provide more accurate assessments of model quality than confidence intervals on the mean values. An inverse N‐weighted least squares approach is impractical as it increases false positive warnings. Physical interpretations are not possible as spurious correlations due to common cycles are not removed. However, SME, Bz, Kp, and Dst are the highest correlates of electron flux, with solar wind velocity, density, and pressure, and IMF magnitude being less well correlated. Plain Language Summary: As high levels of electrons in the radiation belts can damage satellites, an accurate forecasting model is needed. Electron levels can be predicted from regression models using data from the solar wind, the interplanetary magnetic field, and indices measuring disturbances in Earth's magnetic field. Dependable predictions can be made using predictors from either an hour or 3 hr before electron changes occur. A 3 hr ahead prediction is more practical, giving time to respond to electron increases, and results in only slightly lower prediction ability. Key Points: Stepwise regression picks parsimonious predictive models of 4.1–30 keV geostationary electron fluxPredictor correlations with 4.1–30 keV flux are lower than those seen with higher energy electronsHowever, reasonably good predictions can be made at geosynchronous orbit over all MLT [ABSTRACT FROM AUTHOR]

Space weather forecasts are of utmost importance in safeguarding navigation, communication, and electric power system operations, satellites from orbital drag, and the astronauts in the International Space Station from hazardous space radiation during extreme space weather conditions. The finest space weather prediction requires a clear understanding of solar wind‐magnetosphere coupling. The in‐situ measurements of the solar wind properties give unique information about the Sun and its activity on smaller to longer timescales. The present work investigates the influence of solar activity on the coupling of solar wind and Earth's magnetosphere during 23–24 solar cycles. The geomagnetic storms with Symmetric H‐component (SYMH) ≤ −85 nT during the 23–24 solar cycles are considered. We present the results of statistical analysis and relationships between the various solar wind parameters such as the total strength of interplanetary magnetic field (B) and its three‐axis components (Bx, By, and Bz), solar wind proton density (Nsw), solar wind speed (Vsw), SYMH indices, the amplitude, duration, and profile of the geomagnetic storms. The integrated electric field and integrated SYMH index during storms show the highest correlation of 0.92, implying that integrated SYMH is a better proxy of the injected solar wind energy in the magnetosphere in the form of the ring current. Moreover, we do see the difference in the solar wind‐magnetosphere coupling efficiency during the phases of 23–24 solar cycles which is intriguing. Key Points: First observation: The Integrated Ey of solar wind and Integrated Symmetric H‐component show a strikingly high correlationSolar Wind (SW)‐Magnetosphere (M) coupling shows higher average efficiency during the 24th solar cycle compared to the 23rdLow solar activity (or solar minimum) shows elevated efficiency of SW‐M coupling [ABSTRACT FROM AUTHOR]