Search

We select and investigate six global solar extreme-ultraviolet (EUV) wave events using data from the Solar Dynamics Observatory and the Solar and Heliospheric Observatory. These eruptions are all on the limb but recorded as halo coronal mass ejections (CMEs) because the CME-driven shocks have expanded laterally to the opposite side. With the limb observations avoiding the projection effect, we have measured the inclination and speed of the EUV wavefront from 1.05 to 1.25 R ⊙. We also investigate the coupling and connection of the EUV wavefront with the CME boundary and the CME-driven shock, respectively. The major findings in the six events are: (1) the forward inclination of the primary and coronal-hole-transmitted EUV wavefronts is estimated, respectively, and the origins of these inclinations and their effects on the estimate of actual wavefronts speed are investigated; (2) the wavefront speed can be elevated by loop systems near the coronal base, and the average speed in the low corona has no clear correlation with the lateral expansion of the CME-driven shock in the high corona; (3) the fast magnetosonic Mach number of the wavefront is larger than unity from the coronal base; (4) the EUV wavefront is coupled with the CME driver throughout the propagation in two events; (5) after the EUV wavefront vanishes, the CME-driven shock continues traveling on the opposite side and disconnects from the EUV wavefront in four events. These results and their implications are discussed, which provide insight into the properties of global EUV waves. [ABSTRACT FROM AUTHOR]

In this paper, we present for the first time a comprehensive statistical study between type II radio bursts from the metric (m) to the dekameric–hectometric (DH) domain and their associated solar and space weather (SW) phenomena, namely, solar flares (SFs), sunspot (SN) configurations, filament eruptions, coronal mass ejections (CMEs), their interplanetary (IP) counterparts (ICMEs) and shocks, in situ detected particles and geomagnetic storms (GSs). The m-only and m + DH radio signatures are identified from dynamic spectra provided by the ground-based RSTN stations distributed over the globe together with Wind/WAVES satellite data. The DH-only type IIs are adopted from a ready catalog based on Wind/WAVES spacecraft data. We perform the temporal and spatial association between the radio emission and the listed above activity events during solar cycle (SC) 24, separately for the three sub-categories, m-only, m + DH and DH-only type IIs. A quantitative assessment on the occurrence rates is presented as a function of the strength of the specific SW phenomena: highest rates are obtained with CMEs, SFs, filament eruptions, and SN configurations, whereas a much weaker relationship is found with ICMEs, IP shocks, energetic particles, and GSs. The potential of the obtained rates to be used in empirical or physics-based models for SW forecasting is discussed. [ABSTRACT FROM AUTHOR]

Magnetic flux ropes (MFRs) at the center of interplanetary coronal mass ejections (ICMEs) are often characterized as simplistic cylindrical or toroidal tubes with field lines that twist around the cylinder or torus axis. Recent multipoint observations suggest that the overall geometry of these large-scale structures may be significantly more complex. As such, contemporary modeling approaches are likely insufficient to properly understand the global structure of any ICME. In an attempt to rectify this issue, we have developed a novel flux rope modeling approach that allows for the description of arbitrary distortions of the flux rope cross section or deformation of the magnetic axis. The resulting distorted MFR model is a fully analytic model that can be used to describe a complex geometry and is numerically efficient enough to be used for event reconstructions. To demonstrate the usefulness of our approach, we focus on a specific implementation of our model and apply it to an ICME event that was observed in situ on 2023 April 23 at the L1 point by the Wind spacecraft and also by the STEREO-A spacecraft, which was 10.°2 further east and 0.°9 south in heliographic coordinates. We demonstrate that our model can accurately reconstruct each observation individually and also gives a fair reconstruction of both events simultaneously using a multipoint reconstruction algorithm, which results in a geometry that is inconsistent with a cylindrical or toroidal approximation. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) from pseudostreamers represent a significant fraction of large-scale eruptions from the Sun. In some cases, these CMEs take a narrow jet-like form reminiscent of coronal jets; in others, they have a much broader fan-shaped morphology like CMEs from helmet streamers. We present results from a magnetohydrodynamic simulation of a broad pseudostreamer CME. The early evolution of the eruption is initiated through a combination of breakout interchange reconnection at the overlying null point and ideal instability of the flux rope that forms within the pseudostreamer. This stage is characterized by a rolling motion and deflection of the flux rope toward the breakout current layer. The stretching out of the strapping field forms a flare current sheet below the flux rope; reconnection onset there forms low-lying flare arcade loops and the two-ribbon flare footprint. Once the CME flux rope breaches the rising breakout current layer, interchange reconnection with the external open field disconnects one leg from the Sun. This induces a whip-like rotation of the flux rope, generating the unstructured fan shape characteristic of pseudostreamer CMEs. Interchange reconnection behind the CME releases torsional Alfvén waves and bursty dense outflows into the solar wind. Our results demonstrate that pseudostreamer CMEs follow the same overall magnetic evolution as coronal jets, although they present different morphologies of their ejecta. We conclude that pseudostreamer CMEs should be considered a class of eruptions that are distinct from helmet-streamer CMEs, in agreement with previous observational studies. [ABSTRACT FROM AUTHOR]

Starting in the evening of 10 May 2024 the Earth's magnetosphere was hit by the coronal mass ejections (CMEs) creating the largest geomagnetic storm in ∼ ${\sim} $20 years. The CME encounter was characterized by variations of plasma number density and magnetic field. Here, I present the ARTEMIS observations at the lunar orbit during this event. The IMF bz ${b}_{z}$ ranged from −60 to +40 nT both with ∼ ${\sim} $hour to minutes periodicity with plasma jets propagating in ±zGSE $\pm {z}_{\mathit{GSE}}$‐direction within multi‐scale wave structures. Similar signature has been recently reported at the magnetopause by MMS spacecraft (Li et al., 2023, https://doi.org/10.1029/2023GL105539; Nykyri, 2024, https://doi.org/10.1029/2024GL108605) during a strongly southward IMF. Here, I show that the CME boundaries were KH unstable leading to multi‐scale density and magnetic field fluctuations including reconnection jets. The wavelengths varied from ∼ ${\sim} $60 to 270 RE ${R}_{E}$, suggesting that the magnetosphere was periodically exposed to successive intervals of strongly northward and southward IMF leading to enhanced mass and magnetic flux loading. Plain Language Summary: Coronal mass ejections (CMEs) are giant explosions of plasma and magnetic field from the Sun which can produce beautiful Auroras, but also destroy our satellites, power delivery networks, and avionics systems. The seriousness of the storm depends on the pre‐existing conditions of the magnetosphere, the strength and orientation of the magnetic field within the CME structure, its size and speed which drives its duration, as well as the properties of the plasma within it. In this paper, I discuss and analyze the CME observations during the recent Mother's day storm (started on 10 May 2024) using the ARTEMIS spacecraft data at the lunar orbit. During the CME encounter, the SC were exposed to periodic north‐south‐variations of the magnetic field orientation and plasma density which allowed the Earth's magnetosphere to be successively filled with plasma, and magnetic flux likely enabling its effective acceleration in large‐quantities. I show that these periodic variations were produced by giant ∼ ${\sim} $ 60–270 RE ${R}_{E}$ waves at the boundary of the CMEs, such that the entire Earth's magnetosphere was surfing the crests and troughs of these waves, and absorbing the kinetic and magnetic energy from the solar wind. Key Points: Velocity shear at the boundary of a coronal mass ejection (CME) ejecta created Kelvin‐Helmholtz Instability (KHI) ∼ ${\sim} $7 million km upstream the Earth‐Sun L‐1 pointKHI generated multi‐scale density and IMF bz ${b}_{z}$ fluctuations from −60 to +40 nT at the boundary layers of the CME ejecta encountersKH wavelengths varied from ∼ ${\sim} $60 to ∼ ${\sim} $270 RE ${R}_{E}$ implying periodic and successive mass and magnetic flux loading of the magnetosphere system [ABSTRACT FROM AUTHOR]

Interplanetary coronal mass ejections (ICMEs), characterized by their magnetic flux ropes, could potentially trigger geomagnetic disturbances. They have been attracting extensive investigations for decades. Despite numerous ICME models proposed in the past, few account for the curvature of the flux rope axis. In this study, we use conjunction observations from ACE, STEREO A and B, Juno and Solar Orbiter to analyze the evolution of the rope orientation of ICME flux ropes. Our findings indicate that the orientation of these ropes changes independently of the scale of the ropes or the distance they travel between spacecrafts. Furthermore, we estimate and compare the major radii of these flux ropes, uncovering a diverse range of distributions that do not seem to depend on the flux rope's width. These results provide fresh insights and constraints for global ICME models, thereby contributing to the advancement of space weather research. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) are solar eruptions that involve large-scale changes to the magnetic topology of an active region. There exists a range of models for CME onset which are based on twisted or sheared magnetic field above a polarity inversion line (PIL). We present observational evidence that topological changes at PILs, in the photosphere, form a key part of CME onset, as implied by many models. In particular, we study the onset of 30 CMEs and investigate topological changes in the photosphere by calculating the magnetic winding flux, using the artop code. By matching the times and locations of winding signatures with CME observations produced by the almanac code, we confirm that these signatures are indeed associated with CMEs. Therefore, as well as presenting evidence that changes in magnetic topology at the photosphere are a common signature of CME onset, our approach also allows for the finding of the source location of a CME within an active region. [ABSTRACT FROM AUTHOR]

Solar eruptions are sudden release of the magnetic free energy accumulated within a quasi-static evolutionary process of the corona. Interestingly, many solar eruptions are preceded by a short-term slow-rise phase, during which the pre-eruption structure rises at a speed significantly larger than that of the quasi-static evolution. Here we suggest an explanation for the slow-rise phase based on a recent high-accuracy magnetohydrodynamic simulation for initiation of solar eruption. The simulation shows that by continuously shearing a bipolar magnetic arcade, an internal current sheet forms gradually, and an eruption begins once magnetic reconnection is triggered at the current sheet. We find in the simulation that the overlying field presents a slow-rise phase before the reconnection sets in. In addition, the rising speed is significantly larger than that of the core field during this phase. This slow rise is a manifestation of the growing expansion of the arcade in the process of approaching a fully open field state, which is inherent to the formation of a current sheet before the eruption. We also show three flare events with slow-rise phases that are highly consistent with these key characteristics in the simulation: an expansion of the overlying coronal loops with speeds much larger than the quasi-static evolution speed, and for those events with filament eruption, the slow rise of filament is much smaller than that of the overlying loops. In this type of events, the eruption might be initiated through the mechanism as shown in the simulation, and the expansion of overlying coronal loops is a better indicator of the slow-rise phase. [ABSTRACT FROM AUTHOR]

Based on decades of single-spacecraft measurements near 1 au as well as data from heliospheric and planetary missions, multi-spacecraft simultaneous measurements in the inner heliosphere on separations of 0.05–0.2 au are required to close existing gaps in our knowledge of solar wind structures, transients, and energetic particles, especially coronal mass ejections (CMEs), stream interaction regions (SIRs), high speed solar wind streams (HSS), and energetic storm particle (ESP) events. The Mission to Investigate Interplanetary Structures and Transients (MIIST) is a concept for a small multi-spacecraft mission to explore the near-Earth heliosphere on these critical scales. It is designed to advance two goals: (a) to determine the spatiotemporal variations and the variability of solar wind structures, transients, and energetic particle fluxes in near-Earth interplanetary (IP) space, and (b) to advance our fundamental knowledge necessary to improve space weather forecasting from in situ data. We present the scientific rationale for this proposed mission, the science requirements, payload, implementation, and concept of mission operation that address a key gap in our knowledge of IP structures and transients within the cost, launch, and schedule limitations of the NASA Heliophysics Small Explorers program. [ABSTRACT FROM AUTHOR]

Solar filaments are a significant solar activity phenomenon, typically observed in full-disk solar observations in the H-alpha band. They are closely associated with the magnetic fields of solar active regions, solar flare eruptions, and coronal mass ejections. With the increasing volume of observational data, the automated high-precision recognition of solar filaments using deep learning is crucial. In this study, we processed full-disk H-alpha solar images captured by the Chinese H-alpha Solar Explorer in 2023 to generate labels for solar filaments. The preprocessing steps included limb-darkening removal, grayscale transformation, K-means clustering, particle erosion, multiple closing operations, and hole filling. The dataset containing solar filament labels is constructed for deep learning. We developed the Attention U2-Net neural network for deep learning on the solar dataset by introducing an attention mechanism into U2-Net. In the results, Attention U2-Net achieved an average Accuracy of 0.9987, an average Precision of 0.8221, an average Recall of 0.8469, an average IoU of 0.7139, and an average F1-score of 0.8323 on the solar filament test set, showing significant improvements compared to other U-net variants. [ABSTRACT FROM AUTHOR]

In this paper, we model the high-energy tail of observed solar energetic proton energy distributions with a kappa distribution function. We employ a technique for deriving the thermodynamic parameters of solar energetic proton populations measured by the Parker Solar Probe Integrated Science Investigation of the Sun EPI-Hi high-energy telescope, over energies from 10 to 60 MeV. With this technique, we explore, for the first time, the characteristic thermodynamic properties of the solar energetic protons associated with an interplanetary coronal mass ejection (ICME) and its driven shock. We find that: (1) the spectral index or, equivalently, the thermodynamic parameter kappa of solar energetic protons (κ EP) gradually increases, starting from the pre-ICME region (upstream of the CME-driven shock), reaching a maximum in the CME ejecta (κ EP ≈ 3.5), followed by a gradual decrease throughout the trailing portion of the CME; (2) the solar energetic proton temperature and density (T EP and n EP) appear anticorrelated, a behavior consistent with subisothermal polytropic processes; and (3) values of T EP and κ EP appear to be positively correlated, indicating an increasing entropy with time. Therefore, these proton populations are characterized by a complex and evolving thermodynamic behavior, consisting of multiple subisothermal polytropic processes, and a large-scale trend of increasing temperature, kappa, and entropy. This study and its companion study by Livadiotis et al. open up a new set of procedures for investigating the thermodynamic behavior of energetic particles and their shared thermal properties. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is widely believed to be the fundamental process in the solar atmosphere that underlies magnetic energy release and particle acceleration. This process is responsible for the onset of solar flares, coronal mass ejections, and other explosive events (e.g., jets). Here, we report direct imaging of a prolonged plasma/current sheet along with quasiperiodic magnetic reconnection in the solar corona using ultra-high-resolution observations from the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory and the Solar Dynamics Observatory/Atmospheric Imaging Assembly. The current sheet appeared near a null point in the fan–spine topology and persisted over an extended period (≈20 hr). The length and apparent width of the current sheet were about 6″ and 2″, respectively, and the plasma temperature was ≈10–20 MK. We observed quasiperiodic plasma inflows and outflows (bidirectional jets with plasmoids) at the reconnection site/current sheet. Furthermore, quasiperiodic reconnection at the long-lasting current sheet produced recurrent eruptions (small flares and jets) and contributed significantly to the recurrent impulsive heating of the active region. Direct imaging of a plasma/current sheet and recurrent null-point reconnection for such an extended period has not been reported previously. These unprecedented observations provide compelling evidence that supports the universal model for solar eruptions (i.e., the breakout model) and have implications for impulsive heating of active regions by recurrent reconnection near null points. The prolonged and sustained reconnection for about 20 hr at the breakout current sheet provides new insights into the dynamics and energy release processes in the solar corona. [ABSTRACT FROM AUTHOR]

A variety of magnetosphere‐ionosphere current systems and waves have been linked to geomagnetic disturbance (GMD) and geomagnetically induced currents (GIC). However, since many location‐specific factors control GMD and GIC intensity, it is often unclear what mechanisms generate the largest GMD and GIC in different locations. We address this challenge through analysis of multi‐satellite measurements and globally distributed magnetometer and GIC measurements. We find embedded within the magnetic cloud of the 23–24 April 2023 coronal mass ejection (CME) storm there was a global scale density pulse lasting for 10–20 min with compression ratio of ∼10 ${\sim} 10$. It caused substantial dayside displacements of the bow shock and magnetopause, changes of 6RE $6{R}_{E}$ and 1.3−2RE $1.3-2{R}_{E}$, respectively, which in turn caused large amplitude GMD in the magnetosphere and on the ground across a wide local time range. At the time this global GMD was observed, GIC measured in New Zealand, Finland, Canada, and the United States were observed. The GIC were comparable (within factors of 2–2.5) to the largest ever recorded during ≥ ${\ge} $14 year monitoring intervals in New Zealand and Finland and represented ∼ ${\sim} $2‐year maxima in the United States during a period with several Kp≥ ${\ge} $7 geomagnetic storms. Additionally, the GIC measurements in the USA and other mid‐latitude locations exhibited wave‐like fluctuations with 1–2 min period. This work suggests that large density pulses in CME should be considered an important driver of large amplitude, global GMD and among the largest GIC at mid‐latitude locations, and that sampling intervals ≤10s ${\le} 10s$ are required to capture these GMD/GIC. Plain Language Summary: We explore how disturbances in the Earth's magnetic field, known as geomagnetic disturbances (GMD), and the resulting geomagnetically induced currents (GIC) in power systems are influenced by different electrical currents and waves in near‐Earth space. One challenge is the lack of easily accessible data on GIC over long periods, which makes it hard to figure out what factors are most responsible for changes in GIC in different places. Also, there is limited research combining data from satellites with data collected on the ground to figure out exactly how GMD and GIC are generated. To tackle these issues, we looked at data collected by multiple satellites in different parts of near‐Earth space along with data from ground magnetometers and GIC measurements distributed around the world. Our results suggest that density pulses from coronal mass ejections, a particular type of structure in the solar wind, are important in causing significant disturbances in the Earth's magnetic field globally and contribute to some of the largest GIC seen in the mid‐latitude region of United States. We emphasize the importance of taking measurements with high sampling rates (≤10s) $(\le 10s)$ to accurately capture these disturbances and the resulting GIC. Key Points: A density pulse embedded in a coronal mass ejection drives global geomagnetic disturbances (GMD) and geomagnetically induced currents (GIC)Measured GIC's comparable to or exceed reference values in several regions, including 58.1 A in the mid‐latitude region of United StatesLarge‐amplitude density pulses are an important driver of GIC and GMD for mid‐latitude regions with large populations [ABSTRACT FROM AUTHOR]

The Relativistic Electron Proton Telescope (REPT) instrument on the Van Allen Probes observed a double‐peaked inner zone proton population throughout the 7 year lifetime of the mission. M. Hudson et al. (2023) showed that a strong SEP event accompanied by a CME‐shock in early March 2012 provided the Solar Energetic Proton (SEP) source for the higher L trapped proton population, which then diffused radially inward to be observed by REPT at L=2 $L=2$. The study followed trajectories of SEP protons launched isotropically from a sphere at 7 Re for 2.5 hr in fields calculated by the LFM‐RCM global MHD model, which includes electric fields needed to model the transport and trapping of the protons by the shock, and then a radial diffusion simulation was run for 2 years using the result from the test‐particle simulation as the initial condition. The simulation result was compared with REPT measurement in November 2013 and showed reasonable agreement. However, the simulation overestimated the Phase Space Density by a factor of four due to lack of field line curvature scattering during the storm in the model. In this study, a test‐particle simulation is performed for 2 days following the injection and trapping of protons in March 2012 using TS05 fields to simulate the field line curvature scattering of the trapped SEP due to the buildup of the ring current during the geomagnetic storm. The resulting sample distribution was then weighted using the flux at the end of the two‐hour MHD‐test particle simulation. A radial diffusion simulation is then run using the initial profile that included the loss effect, with improved comparison with REPT measurements after 2 years. Key Points: Solar Energetic Proton trapping and radial diffusion explain the double‐peaked proton inner zone observed by Van Allen ProbesExtending test particle simulations through the storm using TS05 fields improves data comparison including FLC scattering lossThree simulation timescales are required to model trapping, FLC loss and radial diffusion [ABSTRACT FROM AUTHOR]

The most detrimental geomagnetically induced currents (GICs) documented to date have all taken place during geomagnetic storms. Yet, the probability of GICs throughout geomagnetic storms driven by different solar wind transients, such as high‐speed streams/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejection (ICME) sheaths and magnetic clouds (MC), is poorly understood. We present an algorithm to detect geomagnetic storms and storm phases, resulting in a catalog of 755 geomagnetic storms from January 1996 to June 2023 with the solar wind drivers. Using these storms and the IMAGE magnetometer network, we study the temporal and spatial evolution of spikes in the time derivative of the horizontal component of the external magnetic field, |dHext/dt| $\vert \mathrm{d}{\boldsymbol{H}}_{\mathrm{e}\mathrm{x}\mathrm{t}}/\mathrm{d}t\vert $, greater than 0.5 nT/s during geomagnetic storms driven by HSS/SIR, sheaths and MCs. Spikes occur more often toward the end of the storm main phase for HSS/SIR and MC‐driven storms, while sheaths have spikes throughout the entire main phase. During the main phase most spikes occur in the morning sector around 05 magnetic local time (MLT) and the extent in MLT is narrowest for MCs and widest for sheaths. However, spikes in the pre‐midnight sector during the main and recovery phases are most prominent for HSS/SIR‐driven storms. During the storm sudden commencement (SSC), three MLT hotspots exist, the post‐midnight at 04 MLT, pre‐noon at 09 MLT and afternoon at 15 MLT. The pre‐noon hotspot has the highest probability of spikes and the widest extent in magnetic latitude. Plain Language Summary: Geomagnetic storms can have damaging implications on technological infrastructures such as power grids, pipelines or railway systems. Those implications arise due to geomagnetically induced currents (GICs) caused by rapid changes in the Earth's magnetic field. In this paper, we present a way to automatically detect geomagnetic storms as well as the key periods of the storm's activity. The primary solar wind structures that cause geomagnetic storms are high‐speed streams and their stream interaction regions (HSS/SIR), sheaths ahead of interplanetary coronal mass ejections and magnetic clouds (MC). Using the detected geomagnetic storms we study spikes in the magnetic field changes in Fennoscandia to map the GIC activity throughout the geomagnetic storms caused by HSS/SIR, sheaths and MCs. We report on several similarities and differences in the evolution and extent of spikes during geomagnetic storms for the different solar wind structures. One such difference is for example, in the likelihood of spikes throughout the storm. For those storms caused by HSS/SIR and MCs spikes are more likely close to the time of maximum geomagnetic storm disturbance, while for storms caused by sheaths spikes are likely at any time from the beginning of the storm to the maximum storm disturbance. Key Points: This paper presents a catalog of geomagnetic storms, their phases and interplanetary drivers from 1996 to 2023During the storm sudden commencement three hotspots of spikes in |dHext/dt| exist, at 04, 09 and 15 magnetic local timeSheath storms have |dHext/dt| spikes occurring during the entire main phase, while for MC and HSS/SIR peak toward the end of the main phase [ABSTRACT FROM AUTHOR]

In this paper, we carry out multiwavelength observations of two successive extreme-ultraviolet (EUV) waves originating from active region (AR) NOAA 13575 and a transverse oscillation of a columnar quiescent prominence on 2024 February 9. A hot channel eruption generates an X3.4 class flare and the associated full-halo coronal mass ejection (CME), which drives the first EUV wave front (WF1) at a speed of |$\sim$| 835 km s |$^{-1}$|⁠. WF1 propagates in the south-east direction and interacts with the prominence, causing an eastward displacement of the prominence immediately. Then, a second EUV wave front (WF2) is driven by a coronal jet at a speed of |$\sim$| 831 km s |$^{-1}$|⁠. WF2 follows WF1 and decelerates from |$\sim$| 788 to |$\sim$| 603 km s |$^{-1}$| before arriving at and touching the prominence. After reaching the maximum displacement, the prominence turns back and swings for 1–3 cycles. The transverse oscillation of horizontal polarization is most evident in 304 Å. The initial displacement amplitude, velocity in the plane of the sky, period, and damping time fall in the ranges of 12–34 Mm, 65–143 km s |$^{-1}$|⁠ , 18–27 min, and 33–108 min, respectively. There are strong correlations among the initial amplitude, velocity, period, and height of the prominence. Surprisingly, the oscillation is also detected in 1600 Å, which is totally in phase with that in 304 Å. [ABSTRACT FROM AUTHOR]

Analogous to solar flares, stellar flares are dramatic explosions in the atmosphere, which may be accompanied by prominence eruptions, coronal mass ejections (CMEs), and other forms of plasma motion. Based on time-resolved spectroscopic observations of the RS CVn-type star II Peg, we aim to search for the potential plasma motions associated with flares. In these observations, we detected part of the gradual decay phase of an optical flare, for which we find a lower limit on the energy of the Hα line of 6.03 × 1033 erg. Converting this Hα energy, we find a bolometric white-light energy of 3.10 × 1035 erg. Moreover, a secondary peak is also observed. After removing a quiescence reference, the Hα residual shows an asymmetric behavior, including both a blueshifted and a redshifted emission component. The former component has a bulk velocity of about −180 km s−1 and extends its velocity to more than −350 km s−1. This phenomenon is likely caused by a prominence eruption event or a chromospheric evaporation process. The latter emission component has a bulk velocity of 130–70 km s−1 and extends its velocity to nearly 400 km s−1. We attribute the redshifted emission component to one or a combination of several possible scenarios: flare-driven coronal rain, chromospheric condensation, backward-directed prominence eruption close to the stellar limb, or falling material in a prominence eruption. The minimum masses of the moving plasmas resulting in the blueshifted and redshifted emission components are estimated to be 0.56 × 1020 g and 1.74 × 1020 g, respectively. [ABSTRACT FROM AUTHOR]

Context. Filament eruptions and coronal mass ejections (CMEs) reveal large-scale instabilities of magnetic structures in the solar corona. Some of them are accompanied by radio emission, which at decimetric and longer wavelengths is a signature of electron acceleration that may be different from the acceleration in impulsive flares. The radio emission is part of the broadband continua at decimetre and metre wavelengths called type IV bursts. Aims. In this article we investigate a particularly well-observed combination of a filament eruption seen in Hα and at extreme ultraviolet (EUV) wavelengths and a moving type IV burst on 2021 August 24. The aim is to shed light on the relationship between the large-scale erupting magnetic structure and the acceleration and transport of non-thermal electrons. Methods. We used imaging observations of a moving radio source and associated burst groups with the refurbished Nançay Radioheliograph and whole-Sun radio spectrography from different ground-based and space-borne instruments, in combination with X-ray, radio, and in situ electron observations at tens of keV from Solar Orbiter and EUV imaging by SDO/AIA. The radio sources are located with respect to the erupting magnetic structure traced by the filament (EUV 30.4 nm), and the timing of the electrons detected in situ is compared with the timing of the different radio emissions. Results. We find that the moving radio source is located at the top of the erupting magnetic structure outlined by the filament, which we interpret as a magnetic flux rope. The flux rope erupts in a strongly non-radial direction, guided by the overlying magnetic field of a coronal hole. The electrons detected at Solar Orbiter are found to be released mainly in two episodes, 10–40 minutes after the impulsive phase. The releases coincide with two groups of radio bursts, which originate respectively on the flank and near the top of the erupting flux rope. Conclusions. The observation allows an unusually clear association between a moving type IV radio burst, an erupting magnetic flux rope as core structure of a CME, and particle releases into the heliosphere. Non-thermal electrons are confined in the flux rope. Electrons escape to the heliosphere mainly in two distinct episodes, which we relate to magnetic reconnection between the flux rope and ambient open field lines. [ABSTRACT FROM AUTHOR]

Context. Solar filament eruptions usually appear to occur in association with the sudden explosive release of magnetic energy accumulated in long-lived arched magnetic structures. The released energy occasionally drives fast-filament eruptions that can be the source regions of coronal mass ejections. A quantitative analysis of high-speed filament eruptions is thus essential to help elucidate the formation and early acceleration of coronal mass ejections. Aims. The goal of this paper is to investigate the dynamic processes of a fast-filament eruption by using unprecedented high-resolution full-disk Hα imaging spectroscopy observations. Methods. The whole process of the eruption was captured in a wide spectral window of the Hα line (±9.0 Å), which allowed for the detection of highly Doppler-shifted plasma. By applying the "cloud model" and obtaining two-dimensional optical thickness spectra, we derived the Doppler velocity; the true eruption profiles (height, velocity, and acceleration); and the trajectory of the filament eruption in 3D space. Results. The Doppler velocity maps show that the filament was predominantly blueshifted. During the main and final process of the eruption, strongly blueshifted materials manifest, traveling with velocities exceeding 250 km s−1. The spectral analysis further revealed that the erupting filament is made of multiple components, some of which were Doppler-shifted approximately to −300 km s−1. We found that the filament eruption attains a maximum true velocity and acceleration of about 600 km s−1 and 2.5 km s−2, respectively, and its propagation direction deviates from the radial direction. On the other hand, downflows manifested as redshifted plasma close to the footpoints of the erupting filament move with velocities of 45–125 km s−1. We interpret these redshifted signatures as draining material and therefore as mass loss of the filament, which has implications for the dynamic and the acceleration process of the eruption. Furthermore, we have estimated the total mass of the Hα filament, resulting in ∼5.4 × 1015 g. [ABSTRACT FROM AUTHOR]

Context. Coronal mass ejections (CMEs) stand as intense eruptions of magnetized plasma from the Sun, and they play a pivotal role in driving significant changes of the heliospheric environment. Deducing the properties of CMEs from their progenitors in solar source regions is crucial for space weather forecasting. Aims. The primary objective of this paper is to establish a connection between CMEs and their progenitors in solar source regions, enabling us to infer the magnetic structures of CMEs before their full development. Methods. We created a dataset comprising a magnetic flux rope series with varying projection shapes (S-, Z-, and toroid-shaped), sizes, and toroidal fluxes using the Regularized Biot-Savart Laws (RBSL). These flux ropes were inserted into solar quiet regions with the aim of imitating the eruptions of quiescent filaments. Thereafter, we simulated the propagation of these flux ropes from the solar surface to a distance of 25 R⊙ with our global coronal magnetohydrodynamic (MHD) model COCONUT. Results. Our parametric survey revealed significant impacts of source flux ropes on the consequent CMEs. Regarding the flux-rope morphology, we find that the projection shape (e.g., sigmoid or torus) can influence the magnetic structures of CMEs at 20 R⊙, albeit with minimal impacts on the propagation speed. However, these impacts diminish as source flux ropes become fat. In terms of toroidal flux, our simulation results demonstrate a pronounced correlation with the propagation speed of CMEs as well as the successfulness in erupting. Conclusions. This work builds the bridge between the CMEs in the outer corona and their progenitors in solar source regions. Our parametric survey suggests that the projection shape, cross-section radius, and toroidal flux of source flux ropes are crucial parameters in predicting magnetic structures and the propagation speed of CMEs, providing valuable insights for space weather prediction. On the one hand, the conclusion drawn here could be instructive in identifying the high-risk eruptions with the potential to induce stronger geomagnetic effects (Bz and propagation speed). On the other hand, our findings hold practical significance for refining the parameter settings of launched CMEs at 21.5 R⊙ in heliospheric simulations, such as with EUHFORIA, based on observations for their progenitors in solar source regions. [ABSTRACT FROM AUTHOR]

We present the study of two solar eruptive events observed on December 7 2020 and October 28 2021. Both events were associated with full halo coronal mass ejections (CMEs) and flares. These events were chosen because they show a strong non-radial direction of propagation in the low corona and their main propagation direction observed in the inner heliosphere is not fully aligned with the Sun-Earth line. This characteristic makes them suitable for our study, which aims to inspect how the non-radial direction of propagation in the low corona affects the time of CMEs' arrival at Earth. We reconstructed the CMEs using SOHO/LASCO and STEREO/COR observations and modelled them with the 3D MHD model EUHFORIA and the cone model for CMEs. In order to compare the accuracy of forecasting the CME and the CME-driven shock arrival time at Earth obtained from different methods, we also used so-called type II bursts, radio signatures of associated shocks, to find the velocities of the CME-driven shocks and forecast the time of their arrival at Earth. Additionally, we estimated the CME arrival time using the 2D CME velocity obtained from the white light images. Our results show that the lowest accuracy of estimated CME Earth arrival times is found when the 2D CME velocity is used (time difference between observed and modelled arrival time, Δt ≈ −29 h and −39 h, for the two studied events, respectively). The velocity of the type II radio bursts provides somewhat better – but still not very accurate – results (Δt ≈ +21 h and −29 h, for the two studied events, respectively). Employing, as an input to EUHFORIA, the CME parameters obtained from the graduated cylindrical shell (GCS) fittings at consequently increasing heights, results in a strongly improved accuracy of the modelled CME and shock arrival time; Δt changes from 20 h to 10 min in the case of the first event, and from 12 h to 30 min in the case of the second one. This improvement shows that when we increased the heights of the GCS reconstruction we accounted for the change in the propagation direction of the studied CMEs, which allowed us to accurately model the CME flank encounter at Earth. Our results show the great importance of the change in the direction of propagation of the CME in the low corona when modelling CMEs and estimating the time of their arrival at Earth. [ABSTRACT FROM AUTHOR]

Context. Shock waves in the solar corona are associated with solar flares and coronal mass ejections (CMEs). Type II solar bursts are radio signatures of shock waves in the solar corona. They are driven by solar flares or CMEs. Despite extensive studies, the intricate spectral patterns observed in type II solar bursts occasionally pose new challenges for the theory of electron acceleration in shocks. Aims. We study a newly identified feature in type II solar bursts called spectral cleaving. This feature is characterized by the actual branching of a type II radio emission lane in radio spectral data. Methods. We analyzed the type II burst exhibiting spectral cleaving in high-fidelity dynamic spectra obtained using the URAN-2 radio telescope (8.25–33 MHz; Poltava region, Ukraine) on 2011 February 14. The high-resolution spectrograms were examined to ascertain its spectral morphology. Results. Our research represents the first recognition of spectral cleaving as a peculiarity of type II bursts that is yet to be classified. This effect occurs due to the shift (or migration) of radio source(s) along a shock front, which in turn is caused by changes in the magnetic field orientation ahead of the propagating shock front. Conclusions. The spectral cleaving observed in solar type II bursts reveals a distinct phenomenon that indicates complex interactions between shock waves and magnetic fields in the solar corona. This discovery enhances our understanding of the mechanisms behind solar radio emissions and emphasizes the need for further observational studies to verify these findings. [ABSTRACT FROM AUTHOR]

Understanding and predicting the geoeffectiveness of solar activity on Earth is crucial for space weather. Therefore, predicting the impact of coronal mass ejections (CMEs) and their associated interplanetary (IP) shocks on Earth is essential. Observations of CMEs near the Sun can be used for these prediction and to study their propagation and evolution in IP space. Commonly used international models do not accurately predict whether and when IP shocks would reach Earth, thus failing to meet the demands of space weather forecasting. This study investigated the geoeffectiveness of solar-IP disturbance events, focusing on type II radio bursts from 1996 to 2019 (solar cycles 23 and 24). The study results showed that during this period, Wind/WAVES detected 623 type II bursts and 541 IP shocks at the L1 point, where 181 type II bursts were associated with L1 shocks. Approximately 29% of the IP shocks associated with type II bursts reached Earth, and approximately 34% of the IP shocks at the L1 point were accompanied by these bursts. IP type II radio bursts and their cutoff frequencies can serve as indicators of the geoeffectiveness of CMEs towards Earth. IP shocks accompanied by type II radio bursts cause stronger geomagnetic responses than those without the associated type II radio bursts. Lower cutoff frequencies of type II radio bursts increase the probability that the corresponding shocks reaching Earth, intensifying the geomagnetic response of the shock. Consequently, the presence of IP type II radio bursts and can serve as indicators of geoeffectiveness of the Earth-directed CMEs. Further, they help improve the accuracy of forecasting the geoeffectiveness of CME/shock events towards Earth. [ABSTRACT FROM AUTHOR]

The current sheet is an essential feature in solar flares and is the primary site for magnetic reconnection and energy release. Imaging observations feature a long linear structure above the candle-flame-shaped flare loops, which resembles the standard flare model with the current sheet viewed edge-on. We investigate the thermal properties of plasmas surrounding the linear sheet during flares, using EUV observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The differential emission measure analyses show evidence of high temperatures in the plasma sheets (PSs), containing hot emissions from only a narrow temperature range, suggestive of an isothermal feature. The sheet temperature remains constant at different heights above the flare arcade, peaking at around log T = 7.0–7.1; while the well-studied 2017 September 10 X8.2 flare serves as an exception in that the temperature decreases with increasing height and peaks higher ( log T = 7.25) during the gradual phase. Most PS cases also hold similar emission measures and thicknesses; while the PS emissions drop exponentially above the flare arcade, the sheet thicknesses show no significant height association as for all the measurements. The characteristics of isothermal and steady temperature suggest balanced heating and cooling processes along the current sheet; in particular, additional heating may exist to compensate for the conductive and radiative cooling away from the reconnection site. Our results suggest a steady and uniform sheet structure in the macroscopic scale that results from flare reconnection. [ABSTRACT FROM AUTHOR]

Low-magnitude (FD(%) ≥ − 3 % ) Forbush decreases (FDs) and their space weather linkages are recently becoming popular in the literature. Accurate timing and correct magnitude measurement of weak FDs are a desideratum. This demands disentangling the effects of the ever present cosmic ray (CR) diurnal wave that exerts undesirable influence on CR data. An enhanced version of a recently developed algorithm has been deployed to decompose raw CR data at Apatity (APTY) and Moscow (MOSC) neutron monitor (NM) stations into low and high frequency signals. A subroutine in the Fast Fourier transform software simultaneously calculates the magnitude and the epoch time of the events from the transformed data. The software selected 335 and 359 low magnitude FDs respectively for APTY and MOSC observatories. The large catalogues of low-amplitude FDs selected compared to those in literature may be attributed to the efficiency of the present algorithm. We carried out a regression analysis on the magnitude of these events and the corresponding solar wind disturbance agents. The analysis shows that for the APTY NM station, the correlation coefficient results r for FD-interplanetary magnetic field (IMF) and FD-planetary geomagnetic activity index (ap) relations are statistically significant at 95% confidence level. At the MOSC station, we find r ∼ −0.41 statistically significant at 95% confidence level for FD-solar wind speed (SWS) relation (after removing events due to co-rotating interaction regions). Analyzing all (low- and high-amplitude) FDs, r is relatively strong and statistically significant at 95% confidence level. The implications of these findings are discussed. [ABSTRACT FROM AUTHOR]

Decades of in-situ solar-wind measurements have clearly established the variation of solar-wind physical parameters. These variable parameters have been used to classify the solar-wind magnetized plasma into different types, leading to several classification schemes being developed. These classification schemes, while useful for understanding the solar wind's originating processes at the Sun and early detection of space weather events, have left open questions regarding which physical parameters are most useful for classification and how recent advances in our understanding of solar-wind transients impact classification. In this work, we use neural networks trained with different solar-wind magnetic and plasma characteristics to automatically classify the solar wind in coronal hole, streamer belt, sector reversal and solar transients such as coronal mass ejections comprised of both magnetic obstacles and sheaths. Furthermore, our work demonstrates how probabilistic neural networks can enhance the classification by including a measure of prediction uncertainty. Our work also provides a ranking of the parameters that lead to an improved classification scheme with ∼ 96 % accuracy. Our new scheme paves the way for incorporating uncertainty estimates into space-weather forecasting with the potential to be implemented on real-time solar-wind data. [ABSTRACT FROM AUTHOR]

We analyzed 58 high-energy proton events that occurred during the years 1996 – 2022. In 32 out of the 58 (55%) events, the proton energies extended up to ∼ 68 MeV but did not reach 100 MeV. In the remaining 26 events, the proton energies exceeded 100 MeV. We studied the differences in the characteristics of these proton events and their associations with solar and interplanetary phenomena to improve understanding proton sources and acceleration processes. The coronal mass ejections (CMEs) associated with > 100 MeV proton events appeared to be, on average, more energetic than those associated with < 100 MeV proton events. The peak and integrated fluxes (fluence) of the soft X-ray (SXR) flares were higher in > 100 MeV proton events, but there was almost no difference in the rise times of the flares. In a major part of the > 100 MeV proton events, protons were released over the rise phase of the SXR flares, whereas in most of the < 100 MeV events the proton releases occurred after the peak of the SXR flares. We established limits for the CME speed VCME and SXR peak flux Fpk or total fluence Fi, which helped us to distinguish the events in the two groups. Solar eruptions with VCME > 1000 km s−1 and F > pk 5 ⋅ 10 − 5 W m−2 had a high probability to produce proton events of > 100 MeV. On the other hand, eruptions with V > CME 900 km s−1 and F < i 5 ⋅ 10 − 4 J m−2 and eruptions with V < CME 900 km s−1 irrespective of the SXR total fluence were very likely to produce proton events of < 100 MeV. All proton events were associated with decametric Type III radio bursts, and most of them had Type II bursts associations either in metric or decametric–hectometric (DH) wavelengths or both. Both metric- and DH-Type II emissions were observed in 50% of < 100 MeV proton events while they were observed in 88% of > 100 MeV events. Our analysis showed that protons in most of the > 100 MeV events were released low in the corona (≤ 3.0 R⊙) before the onsets of the DH-Type II radio bursts. Conversely, protons in most of the < 100 MeV events were released higher in the corona (> 3 R⊙) and after the DH-Type II onsets. We conclude that protons in most of the > 100 MeV events are accelerated either by the flare reconnection processes or by shocks low in the corona and could undergo reacceleration higher in the corona in CME shocks manifested in DH-Type II radio emission. In the < 100 MeV events, protons are mainly accelerated in CME shocks at coronal heights > 3 R⊙. [ABSTRACT FROM AUTHOR]

The SOL2012-05-17 event is remarkable in that it caused one of two ground-level enhancements (GLE71) in Solar Cycle 24. Despite the efforts spent studying this solar event, some aspects of it remain unclear. This relates to the development of a coronal mass ejection (CME), the history of the shock wave, and the flare. Our measurements reveal the following chain of phenomena. Two successive eruptions occurred within a few minutes. The rate of change of the reconnected magnetic flux shows a series of increases corresponding to the acceleration or deceleration of the erupting structures. The temporal profile of the magnetic-flux change rate is similar to the hard X-ray burst. Each eruption excited a disturbance that, propagating outward, accelerated all structures above it. This led to complex kinematic characteristics of the erupting structures that eventually formed a self-similarly expanding CME. The two disturbances became piston shocks and merged into a single, stronger shock. There are indications of transformation of the piston shock into a bow shock, but this occurs at distances exceeding ten solar radii. Components of the described picture were observed in a number of events and can serve as a guide for studies of eruptive flares. [ABSTRACT FROM AUTHOR]

A reliable data analysis center plays a crucial role in the successful execution of a space mission. The Science Operation and Data analysis Center (SODC) of Advanced Space-based Solar Observatory (ASO-S) is a bridge between the science team of ASO-S and data users (Huang et al. 2019). ASO-S plays a crucial role in understanding the solar eruptions (such as flares and coronal mass ejections) and the magnetism behind them. In this article, we outline the current status of ASO-S, as well as its data products and analysis software. These resources aid in the enhanced understanding of solar magnetism and its associated energetic eruptions. [ABSTRACT FROM AUTHOR]

We present a statistical study on the relationship of solar dynamic events (solar flares and coronal mass ejections) with active regions during Solar Cycle 24 (December 2008–December 2019). Combining data from NOAA Space Weather Prediction Center and observations of Large Angle and Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) spacecraft, we found that more than a half of the coronal mass ejections were generated inside active regions. Geostationary Operational Environmental Satellite (GOES) soft X-ray flare listing data completed our study showing that almost 83% of Solar Cycle 24 flares are connected with active regions. Finally, we summarize the details for the related phenomena into an online catalog based on a list of all 1533 active regions that produced at least one flare and/or coronal mass ejection during Solar Cycle 24 and explore their properties like flare class, coronal mass ejection speed, and angular width paying special attention to the most powerful and threatful to Earth solar events. [ABSTRACT FROM AUTHOR]

A comparison of three types of ionosonde data from Europe during an interplanetary coronal mass ejection (ICME)- and a corotating interaction region (CIR)-driven geomagnetic storm event is detailed in this study. The selected events are 16–20 March 2015 for the ICME-driven storm and 30 May to 4 June 2013 for the CIR-driven one. Ionospheric data from three European ionosonde stations, namely Pruhonice (PQ), Sopron (SO) and Rome (RO), are investigated. The ionospheric F2-layer responses to these geomagnetic events are analyzed with the ionospheric foF2 and h'F2 parameters, the calculated deltafoF2 and deltahF2 values, the ratio of total electron content (rTEC) and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite Global Ultraviolet Imager (GUVI) thermospheric [O]/[N2] measurement data. The storm-time and the quiet-day mean values are also compared, and it can be concluded that the quiet-day curves are similar at all the stations while the storm-time ones show the latitudinal dependence during the development of the storm. As a result of the electron density comparison, during the two events, it can be concluded that the sudden storm commencement (SSC) that characterized the ICME induced a traveling atmospheric disturbance (TAD) seen in the European stations in the main phase, while this is not seen in the CIR-driven ionospheric storm, which shows a stronger and more prolonged negative effect in all the stations, probably due to the season and the depleted O/N2 ratio. [ABSTRACT FROM AUTHOR]

A novel tool utilizing machine learning techniques was designed to forecast ap index values for the next three consecutive days (24 values). The tool employs time series data from the 3 h ap index of solar cycles 23 and 24 to train the Long Short-Term Memory (LSTM) model, predicting ap index values for the next 72 h at three-hour intervals. During periods of quiet geomagnetic activity, the LSTM model's performance is sufficient to yield favorable outcomes. Nevertheless, during geomagnetically disturbed conditions, such as geomagnetic storms of different levels, the model needs to be adapted in order to provide accurate ap index results. In particular, when coronal mass ejections occur, the ap Prediction tool is modulated by inserting predominant features of coronal mass ejections such as the date of the event, the estimated time of arrival and the linear speed. In the present work, this tool is described thoroughly; moreover, results for G2 and G3 geomagnetic storms are presented. [ABSTRACT FROM AUTHOR]

As the current solar cycle 25 progresses and moves towards solar maxima, solar activity is increasing and extreme space weather events are taking place. Two severe geomagnetic storms accompanied by two large Forbush decreases in galactic cosmic ray intensity were recorded in March and May, 2024. More precisely, on 24 March 2024, a G4 (according to the NOAA Space Weather Scale for Geomagnetic Storms) geomagnetic storm was registered, with the corresponding geomagnetic indices Kp and Dst equal to 8 and −130 nT, respectively. On the same day, the majority of ground-based neutron monitor stations recorded an unusual Forbush decrease. This event stands out from a typical Forbush decrease because of its high amplitude decrease phase and rapid recovery phase, i.e., 15% decrease and an extremely rapid recovery of 10% within 1.5 h, as recorded at the Oulu neutron monitor station. Furthermore, on 10–13 May 2024, an unusual G5 geomagnetic storm (geomagnetic indices Kp = 9 and Dst = −412 nT) was registered (the last G5 storm had been observed in 2003). In addition, the polar neutron monitor stations recorded a Ground Level Enhancement (GLE74) during the recovery phase of a large Forbush decrease of 15%, which started on 10 May 2024. In this study, a detailed analysis of these two severe events in regard to the accompanying solar activity, interplanetary conditions and solar energetic particle events is provided. Moreover, the results of the NKUA "GLE Alert++ system", the NKUA/IZMIRAN "FD Precursory Signals" method and the NKUA "ap Prediction tool" concerning these events are presented. [ABSTRACT FROM AUTHOR]

Coronal mass ejections from the Sun are not always initiated along a radial trajectory; such non-radial eruptions are well known to be caused by the asymmetry of the pre-eruption magnetic configuration, which is primarily determined by the uneven distribution of magnetic flux at the photosphere. Therefore, it is naturally expected that the non-radial eruptions should be rather common, at least as frequent as radial ones, given the typically asymmetrical nature of photospheric magnetic flux. However, statistical studies have shown that only a small fraction of eruptions display non-radial behaviour. Here we aim to shed light on this counterintuitive fact, based on a series of numerical simulations of eruption initiation in bipolar fields with different asymmetric flux distributions. As the asymmetry of the flux distribution increases, the eruption direction tends to deviate further away from the radial path, accompanied by a decrease in eruption intensity. In case of too strong asymmetry, no eruption is triggered, indicating that excessively inclined eruptions cannot occur. Therefore, our simulations suggest that asymmetry plays a negative role in producing eruption, potentially explaining the lesser frequency of non-radial solar eruptions compared to radial ones. With increasing asymmetry, the degree of non-potentiality the field can attain is reduced. Consequently, the intensity of the pre-eruption current sheet decreases, and reconnection becomes less efficient, resulting in weaker eruptions. [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 paper, we demonstrate the applicability of the data‐driven solar energetic particle (SEP) model, SOlar‐wind with FIeld‐lines and Energetic‐particles (SOFIE), to simulate the acceleration and transport processes of SEPs and make forecast of the energetic proton flux at energies ≥10 MeV that will be observed near 1 AU. The SOFIE model is built upon the Space Weather Modeling Framework developed at the University of Michigan. In SOFIE, the background solar wind plasma in the solar corona and interplanetary space is calculated by the Stream‐Aligned Aflvén Wave Solar‐atmosphere Model(‐Realtime) driven by the near‐real‐time hourly updated Global Oscillation Network Group solar magnetograms. In the background solar wind, coronal mass ejections (CMEs) are launched by placing an force‐imbalanced magnetic flux rope on top of the parent active region, using the Eruptive Event Generator using Gibson‐Low model. The acceleration and transport processes are modeled by the Multiple‐Field‐Line Advection Model for Particle Acceleration. In this work, nine SEP events (Solar Heliospheric and INterplanetary Environment challenge/campaign events) are modeled. The three modules in SOFIE are validated and evaluated by comparing with observations, including the steady‐state background solar wind properties, the white‐light image of the CMEs, and the flux of solar energetic protons, at energies of ≥10 MeV. Plain Language Summary: In this paper, we describe a physics‐based solar energetic particle (SEP) model, called Solar‐wind with FIeld‐lines and Energetic‐particles (SOFIE). This model is designed to simulate the acceleration and transport processes of SEPs in the solar atmosphere and interplanetary space. SOFIE is built on the Space Weather Modeling Framework developed at the University of Michigan. There are three modules in the SOFIE model, the background solar wind module, the coronal mass ejection (CME) initiation and propagation module, and the particle acceleration and transport module. The background solar wind plasma in the solar corona and interplanetary space is modeled by the Stream‐Aligned Aflvén Wave Solar‐atmosphere Model(‐Realtime) driven by the near‐real‐time hourly updated Global Oscillation Network Group solar magnetograms. In the background solar wind, the CMEs are launched by placing an force‐unbalanced magnetic flux rope on top of the active region, using the Eruptive Event Generator using Gibson‐Low configuration. The acceleration and transport processes are then modeled by the Multiple‐Field‐Line Advection Model for Particle Acceleration. Using SOFIE, we modeled nine historical SEP events. The performance of the model and its capability in making space radiation prediction is discussed. Key Points: The >10 MeV energetic protons can be predicted using the physics‐based model SOlar‐wind with FIeld‐lines and Energetic‐particles (SOFIE)The background of the acceleration and transport processes of energetic protons are resolved using data driven magnetohydrodynamic modelThe default and free parameters of the SOFIE model are evaluated [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]

The Sun continuously affects the interplanetary environment through a host of interconnected and dynamic physical processes. Solar flares, Coronal Mass Ejections (CMEs), and Solar Energetic Particles (SEPs) are among the key drivers of space weather in the near‐Earth environment and beyond. While some CMEs and flares are associated with intense SEPs, some show little to no SEP association. To date, robust long‐term (hours‐days) forecasting of SEP occurrence and associated properties (e.g., onset, peak intensities) does not effectively exist and the search for such development continues. Through an Operations‐2‐Research support, we developed a self‐contained model that utilizes a comprehensive data set and provides a probabilistic forecast for SEP event occurrence and its properties. The model is named Multivariate Ensemble of Models for Probabilistic Forecast of Solar Energetic Particles (MEMPSEP). MEMPSEP workhorse is an ensemble of Convolutional Neural Networks that ingests a comprehensive data set (MEMPSEP‐III by Moreland et al. (2024, https://doi.org/10.1029/2023SW003765)) of full‐disc magnetogram‐sequences and in situ data from different sources to forecast the occurrence (MEMPSEP‐I—this work) and properties (MEMPSEP‐II by Dayeh et al. (2024, https://doi.org/10.1029/2023SW003697)) of a SEP event. This work focuses on estimating true SEP occurrence probabilities achieving a 2.5% improvement in reliability and a Brier score of 0.14. The outcome provides flexibility for the end‐users to determine their own acceptable level of risk, rather than imposing a detection threshold that optimizes an arbitrary binary classification metric. Furthermore, the model‐ensemble, trained to utilize the large class‐imbalance between events and non‐events, provides a clear measure of uncertainty in our forecast. Plain Language Summary: Solar Energetic Particles (SEPs) play an important role in modulating near‐Earth space weather environments affecting communication satellites and posing radiation hazards to astronauts. Because of the complex processes involved reliable early forecast of SEP events still remains a challenge. In this paper, we present an ensemble of models that ingest both solar images and parameters measured by in situ instruments to reliably forecast the chance of SEP event occurrence. Our approach transforms a "yes"/"no" forecast to the probability of event occurrence and provides the users additional flexibility in prioritizing their forecasting goals. Our ensemble of models utilizes the fact that SEP events are much rarer than non‐events and generate uncertainties on predicted probabilities. These uncertainties add value in providing a measure of trust to users in forecasting outcomes. Key Points: End‐to‐End Deep Neural Network model‐ensemble trained on remote sensing + in situ data set for forecast of SEP occurrenceUsage of model ensemble maximizes the use of an imbalanced data set and brings forecasting confidence with uncertainty estimatesCalibration of model outcome to true probability optimizes the forecast reliability acting as a means to step away from the binary forecast [ABSTRACT FROM AUTHOR]

The current study explores the dynamic interaction between Interplanetary coronal mass ejections (ICMEs) and the induced magnetosphere of Venus, utilizing measurements from the Venus Express (VEX) mission. We have investigated 16 ICME events during the period 2006–2013. The altitude of the inbound bow shock and ionopause at Venus are comprehensively studied during the passage of these ICMEs. The ionosphere is found to be highly magnetized due to the very high magnetic pressure of the induced magnetosphere. Remarkably, the altitude of the ionopause is found to be significantly changed as compared to the previous quiet day due to the increased solar wind dynamic pressure Pdyn $\left({P}_{\mathit{dyn}}\right)$. The ratio of the altitude of ionopause and magnitude of the magnetic field (∣B∣) $(\vert B\vert)$ at ionopause on the event days to the quiet days shows a strong anti‐correlation which indicates the ionopause height is inversely related to the magnetic field. Intriguingly, the position of the bow shock exhibited minimal deviations compared to typical quiet days, underscoring that, during ICME events, the ionopause location is more responsive to solar wind pressure fluctuations than the bow shock location. Additionally, the heavy‐ion density near and above the ionopause is found to be significantly higher than that observed on previous quiet days. This substantial increase implies that ICMEs can induce atmospheric loss in Venus's atmosphere and also cause a significant reduction in the ionopause location. Key Points: The ionopause is found to be significantly changed during the passage of ICMEs compared to the quiet time valuesThe bow shock position exhibited minimal deviations during the event compared to typical quiet daysThe heavy‐ion density near and above the ionopause is significantly higher during ICMEs compared to previous quiet days [ABSTRACT FROM AUTHOR]

We estimate the global impact of storms on the global structure and dynamics of the night side plasma sheet from observations by the NASA mission Time History of Events and Macroscale Interactions during Substorms (THEMIS). We focus on an intense storm occurring in December 2015 triggered by interplanetary coronal mass ejections (ICMEs). It starts with a storm sudden commencement (SSC) phase (SYM‐H ∼ ${\sim} $ +50 nT) followed by a growth phase (SYM‐H ∼ ${\sim} $ −188 nT at the minimum) and then a long recovery phase lasting several days. We investigate THEMIS observations when the spacecraft were located in the midnight sector of the plasma sheet at distances typically between 8 and 13 Earth's radii. It is found that the plasma sheet has been globally compressed up to a value of about ∼> ${\sim} > $4 nPa during the SSC and main phases, that is, 8 times larger than its value during the quiet phase before the event. This compression occurs during periods of high dynamic pressure in the ICME (20 nPa) about one order of magnitude larger than its value in the pristine solar wind. We infer a global increase of the lobe magnetic field from 30 to 100 nT, confirmed by THEMIS data just outside the plasma sheet. During the SSC and main phases, the plasma sheet is found thinner by a factor of 2 relative to its thickness at quiet times, while the Tsyganenko T96 magnetic field model shows very stretched magnetic field lines from inner magnetospheric regions toward the night side. During the recovery phase, whereas the interplanetary pressure has dropped off, the plasma sheet tends to gradually recover its quiet phase characteristics (pressure, thickness, magnetic configuration, etc.) during a long recovery phase of several days. Key Points: The global plasma sheet's structure and dynamics are quantified during storms triggered by interplanetary coronal mass ejections using Time History of Events and Macroscale Interactions during Substorms observationsDuring the storm sudden commencement (SSC) and main phases, the magnetotail and plasma sheet have been compressed by a factor of 8 relative to the preceding quiet phaseUsing the T96 model, the plasma sheet is highly stretched during the storm SSC and main phases, gradually returning to the quiet phase [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]

This article presents the first study of the interaction between the Jupiter Icy Moons Explorer (JUICE) spacecraft and the solar wind environment at 1 AU. The state‐of‐the‐art software Spacecraft Plasma Interaction Software was used to simulate the surface charging of the spacecraft and the altered particle environment around the spacecraft. The simulations show that for a typical solar wind environment the spacecraft will charge to around 6 V, with the different dielectric parts of the spacecraft charging to potentials from around −36 to 8 V. For the studied extreme solar wind environment, similar to the environment found in the sheath region inside the shock front of an Interplanetary Coronal Mass Ejection, the surface potential of the spacecraft is lower due to the increased accumulation of electrons. The spacecraft will charge to around 3 V, with the different dielectric surfaces charging from around −45 to 9 V. We also show how the interaction between the spacecraft and its environment alters the ion and electron particle environment around the spacecraft. This study is the first step toward developing correction techniques for the impact that the interaction between the JUICE spacecraft and its environment has on the JUICE charged particle and field measurements. Plain Language Summary: All spacecraft interact with their space environment. This interaction can create a variety of different problems, with a severity that depends on the environment and the design of the spacecraft. Here, we present a study of the interaction between the Jupiter Icy Moons Explorer (JUICE) spacecraft and the solar wind environment at 1 AU. We study both a typical solar wind environment and an extreme environment, for example, the environment encountered during an Interplanetary Coronal Mass Ejection. Our simulations show that we can expect the different parts of the spacecraft to charge from around −45 to 9 V. The interaction between JUICE and the solar wind will also alter the particle environment around the spacecraft. We present the altered charged particle environment around the spacecraft, both for the ion and the various electron populations. This study is the first step toward developing correction techniques for the impact that the interaction between the JUICE spacecraft and its environment has on the JUICE measurements. Key Points: The interaction between the Jupiter Icy Moons Explorer spacecraft and the solar wind environment at 1 AU, is simulatedWe present the spacecraft surface potentials, typically ranging from −45 to 9 V, for different solar wind conditionsWe also present the near spacecraft particle environment, which is altered due to the interaction between the spacecraft and its environment [ABSTRACT FROM AUTHOR]

Interplanetary coronal mass ejections (ICMEs) and the driven geomagnetic storms have a profound influence on the ionosphere, potentially leading to a degradation in positioning performance. In this study, we made a comprehensive analysis of the entire process of the impact of a typical ICME and its driven geomagnetic storm on the low-latitude ionosphere during March 13-14, 2022 (π-day storm) and the positioning performance of Global Navigation Satellite System (GNSS). During the passage of the ICME event, significant ionospheric scintillation, and TEC (total electron content) disturbances were observed in the low-latitude Hong Kong region. The ICME sheath region intensively compressed the magnetosphere via solar wind dynamic pressure enhancement and subsequently drove the storm main phase. It is found that both the magnetospheric compression that formed the storm initial phase and the storm main phase caused ionospheric scintillation. In comparison, the intensity of the ionospheric scintillation caused by the intense magnetospheric compression just before the storm main phase is even more pronounced. We also analyzed the impact of storms on standard point positioning (SPP), precise point positioning (PPP) and real-time kinematic (RTK) techniques. The positioning accuracies of single-frequency SPP and PPP experienced the most severe decline, and there was a noticeable increase in the initialization time for dual-frequency static PPP and RTK during the event. RTK demonstrated a shorter convergence time and higher accuracy during this event, but it was limited to short-baseline RTK (<30 km). [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]

Earth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO2) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO2. The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 1017 J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm. Plain Language Summary: The layer of Earth's atmosphere above 100 km is referred to as the "thermosphere" and can be thought of as the boundary between the space environment above it and the atmosphere below it. In early May 2024, an active sunspot ejected a significant amount of charged particles (protons and electrons) within a strong magnetic field toward Earth. This "coronal mass ejection" or CME encountered Earth's high atmosphere 10–13 May, causing a significant "geomagnetic storm" that significantly heated the thermosphere and modified its chemical composition. The effects of this storm were observed by the SABER instrument which is flying on the NASA Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observes infrared light emitted by carbon dioxide, nitric oxide, molecular oxygen, and ionized nitric oxide produced during the storm. The 10–13 May storm caused the global average infrared radiation levels to increase by nearly a factor of 10 at some wavelengths in 1 day. The storm and the infrared radiation levels dissipated back to pre‐storm levels over the next 2 days. This storm was the third strongest in terms the power (2.64 trillion watts) radiated by the thermosphere in the past 22 years observed by SABER. The observed enhancements in infrared radiation at multiple wavelengths offer the opportunity to more fully understand how the Sun interacts with and influences Earth's highest atmosphere. Key Points: The daily Ap (273 nT) and Dst (−291.94 nT) indexes on 11 May 2024 were the largest since the launch of the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite in December 2001The power radiated 11 May by NO and CO2 exceeded 1 TW each and the NO power (1.41 TW) exceeded the CO2 power (1.35 TW) for the first timeTotal storm radiated power, above background, is 2.64 TW (2.28 × 1017 J), making it the third strongest storm during the TIMED era [ABSTRACT FROM AUTHOR]

Previous simulations have suggested that O+ outflow plays a role in driving the sawtooth oscillations. This study investigates the role of O+ by identifying the differences in ionospheric outflow between sawtooth and non‐sawtooth storms using 11 years of FAST/Time of flight Energy Angle Mass Spectrograph (TEAMS) ion composition data from 1996 through 2007 during storms driven by coronal mass ejections. We find that the storm's initial phase shows larger O+ outflow during non‐sawtooth storms, and the main and recovery phases revealed differences in the location of ionospheric outflow. On the pre‐midnight sector, a larger O+ outflow was observed during the main phase of sawtooth storms, while non‐sawtooth storms exhibited stronger O+ outflow during the recovery phase. On the dayside, the peak outflow shifts significantly toward dawn during sawtooth storms. This strong dawnside sector outflow during sawtooth storms warrants consideration. Plain Language Summary: A sawtooth event is a convection mode in Earth's magnetosphere, which transports solar wind plasma and energy into the inner magnetosphere and ionosphere. Despite three decades since their discovery, the mechanism behind sawtooth oscillations remains uncertain. One theory suggests that O+ outflow induces sawtooth oscillations through an internal feedback mechanism. In line with this theory, some simulations have generated sawtooth oscillations under steady geomagnetic conditions. Furthermore, previous observations indicate that some, but not all, geomagnetic storms exhibit sawtooth oscillations. This study utilizes data from the FAST/TEAMS instrument (1996–2007) and compares O+ outflow variations during geomagnetic storms with and without sawtooth oscillations. Findings indicate that during the storms' initial phase, sawtooth storms produce less O+ outflow than non‐sawtooth storms. Additionally, non‐sawtooth storms exhibit higher O+ outflow in the dayside during the main phase and in the pre‐midnight sector during the recovery phase, challenging the key role of O+ outflow in driving the feedback mechanism. However, observing large O+ outflow in the dawnside sector of sawtooth events suggests more investigation is needed. Key Points: The intensity and location of O+ outflow during storms are different in storms with and without sawtooth oscillationsThe peak dayside outflow is significantly shifted toward dawn during storms with sawtooth observationsThe nightside picture is mixed; the pre‐midnight O+ outflow is higher in the main phase but lower in the recovery phase of sawtooth storms [ABSTRACT FROM AUTHOR]

In recent years, it has become increasingly clear that space weather disturbances can be triggered by transient upstream mesoscale structures (TUMS), independently of the occurrence of large-scale solar wind (SW) structures, such as interplanetary coronal mass ejections and stream interaction regions. Different types of magnetospheric pulsations, transient perturbations of the geomagnetic field and auroral structures are often observed during times when SW monitors indicate quiet conditions, and have been found to be associated to TUMS. In this mini-review we describe the space weather phenomena that have been associated with four of the largest-scale and the most energetic TUMS, namely, hot flow anomalies, foreshock bubbles, travelling foreshocks and foreshock compressional boundaries. The space weather phenomena associated with TUMS tend to be more localized and less intense compared to geomagnetic storms. However, the quiet time space weather may occur more often since, especially during solar minima, quiet SW periods prevail over the perturbed times. [ABSTRACT FROM AUTHOR]