Mass Ejections Research Articles

Recovery of coronal dimmings

Context. Coronal dimmings are regions of reduced emission in the lower corona observed in the wake of coronal mass ejections (CMEs), representing their footprints. Studying the lifetime evolution of coronal dimmings helps us to better understand the recovery and replenishment of the corona after large-scale eruptions. Aims. We study the recovery of dimmings on different spatial scales to enhance our understanding of the replenishment and dynamics of the corona after CMEs. Methods. In order to investigate the long-term evolution of coronal dimming and its recovery, we propose two approaches that focus on both the global and the local evolution of dimming regions: the fixed mask approach and the pixel boxes approach. We present four case studies (September 6, 2011; March 7, 2012; June 14, 2012; and March 8, 2019) in which a coronal dimming is associated with a flare/CME eruption. We analyzed each event with the same methodology, using extreme-ultraviolet filtergrams from the Solar Dynamics Observatory’s Atmospheric Imaging Assembly (SDO/AIA) and Solar TErrestrial RElations Observatory’s Extreme UltraViolet Imager (STEREO/EUVI) instruments. We identified the dimming region by image segmentation, then restricted the analysis to a specific portion of the dimming and tracked the time evolution of the dimming brightness and area. In addition, we study the behavior of small subregions inside the dimming area, of about 3 × 3 pixels, to compare the recovery in different regions of the dimming. Results. Three out of the four cases show a complete recovery 24 hours after the flare/CME eruption. The primary recovery mechanism identified in the observations is the expansion of coronal loops into the dimming region. The recovery of the brightness follows a two-step trend, with a steeper and quicker segment followed by a slower one. In addition, some parts of the dimming, which may be core dimmings, are still present at the end of the analysis time and do not recover within 3 days, whereas the peripheral regions (secondary dimmings) show a full recovery. Conclusions. The high temporal and spatial resolution of SDO/AIA observations combined with multi-view data of the STEREO/EUV instrument reveal high-situated coronal loops expanding after CME eruptions, which cover dimming regions and gradually increase their intensity. Our developed approaches enable the analysis of dimmings alongside these bright structures, revealing different timescales of recovery for core and secondary or twin dimming regions. Combined with magnetic field modeling, these methods lay the foundation for further systematic analysis of dimming recovery and enhance the knowledge gained from already-analyzed events.

Magnetic Field Evolution of the Solar Active Region 13664

On 2024 May 10–11, the strongest geomagnetic storm since 2003 November occurred, with a peak Dst index of −412 nT. The storm was caused by NOAA active region (AR) 13664, which was the source of a large number of coronal mass ejections and flares, including 12 X-class flares. Starting from about May 7, AR 13664 showed a steep increase in its size and (free) magnetic energy, along with increased flare activity. In this study, we perform 3D magnetic field extrapolations with the NF2 nonlinear force-free code based on physics-informed neural networks (R. Jarolim et al.). In addition, we introduce the computation of the vector potential to achieve divergence-free solutions. We extrapolate vector magnetograms from the Solar Dynamics Observatory’s Helioseismic and Magnetic Imager at the full 12 minute cadence from 2024 May 5 00:00 to 11 04:36 UT, in order to understand the AR’s magnetic evolution and the large eruptions it produced. A decrease in the calculated relative free magnetic energy can be related to solar flares in ∼90% of the cases, and all considered X-class flares are reflected by a decrease in the relative free magnetic energy. Regions of enhanced free magnetic energy and depleted magnetic energy between the start and end times of major X-class flares show spatial alignment with brightness increases in extreme-ultraviolet observations. We provide a detailed analysis of the X3.9-class flare on May 10, where we show that the interaction between separated magnetic domains is directly linked to major flaring events. With this study, we provide a comprehensive data set of the magnetic evolution of AR 13664 and make it publicly available for further analysis.

Rates and Beaming Angles of Gamma-Ray Bursts Associated with Compact Binary Coalescences

Some, if not all, binary neutron star (BNS) coalescences, and a fraction of neutron star–black hole (NSBH) mergers, are thought to produce sufficient mass ejection to power gamma-ray bursts (GRBs). However, this fraction, as well as the distribution of beaming angles of BNS-associated GRBs, is poorly constrained from observation. Recent work applied machine learning tools to analyze GRB light curves observed by Fermi/Gamma-Ray Burst Monitor (GBM) and Swift/Burst Alert Telescope (BAT). GRBs were segregated into multiple distinct clusters, with the tantalizing possibility that one of them (BNS cluster) could be associated with BNSs and another (NSBH cluster) with NSBHs. As a proof of principle, assuming that all GRBs detected by Fermi/GBM and Swift/BAT associated with BNSs (NSBHs) lie in the BNS (NSBH) cluster, we estimate their rates (Gpc−3 yr−1). We compare these rates with corresponding BNS and NSBH rates estimated by the LIGO–Virgo–KAGRA (LVK) collaboration from the first three observing runs (O1, O2, O3). We find that the BNS rates are consistent with LVK’s rate estimates, assuming a uniform distribution of beaming fractions (f b ∈ [0.01, 0.1]). Conversely, using the LVK’s BNS rate estimates, assuming all BNS mergers produce GRBs, we are able to constrain the beaming angle distribution to θ j ∈ [0.°8, 33.°5] at 90% confidence. We similarly place limits on the fraction of GRB-bright NSBHs as f B ∈ [1.3%, 63%] (f B ∈ [0.4%, 15%]) with Fermi/GBM (Swift/BAT) data.

A Novel Technique for the Extraction of Dynamic Events in Extreme Ultraviolet Solar Images

High-spatial-resolution images of the solar corona acquired in the extreme ultraviolet (EUV), most notably with the Atmospheric Imaging Assembly (AIA) instrument on the Solar Dynamics Observatory (SDO) reveal the abundance of dynamic events which range from flaring bright points and jets to erupting prominences and coronal mass ejections (CMEs). In this work we present novel techniques to extract such dynamic events from the more steady background corona using 17.1 nm SDO-AIA images. The techniques presented here treat any time series of coronal images as a matrix that can be decomposed into two matrices representing the background and the dynamic component, respectively. The latter has the properties of a so-called sparse matrix, and the proposed methods are classified as methods based on sparse representations. The proposed methods are the median-filter method, the principal component pursuit, and the dynamic-mode decomposition, all of which include data pre-processing using the noise-adaptive fuzzy equalization method. The study reveals that the median-filter method and the dynamic-mode decomposition enhance all motions in the time series and produce similar results. On the other hand, the principal component pursuit enables the clear differentiation of CMEs from the background corona, thus providing a valuable tool for the characterization of their acceleration profiles in the low corona as seen in the EUV.

Predicting the Energy Spectra of Solar Energetic Particles with a Machine Learning Regression Algorithm

Solar energetic particles (SEPs) are a major source of space radiation, especially within the inner heliosphere. These particles, originating from solar flares and coronal mass ejections (CMEs), propagate primarily along interplanetary magnetic fields. The energy spectra of SEP events are crucial for assessing radiation effects and understanding the acceleration and propagation mechanisms in their source regions. In this study, we employed a decision tree regression algorithm with cost complexity pruning to predict SEP energy spectra, including peak flux and integral fluence spectra. This approach uses only solar flares, CMEs, and solar wind data as input parameters and demonstrates strong performance to accurately predict SEP spectra. This method holds significant real-time application value for monitoring and forecasting radiation risks in both deep space and near-Earth environments.

A Model for Flux Rope Formation and Disconnection in Pseudostreamer Coronal Mass Ejections

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.

Distorted Magnetic Flux Ropes within Interplanetary Coronal Mass Ejections

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.

Three-part structure of a solar coronal mass ejection observed in low coronal signatures of Solar Orbiter

Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the Sun propagating through the heliosphere. Observations of the March 28, 2022, event provide unique images of a three-part solar CME in the low corona in active region 12975: a bright core or filament, a dark cavity, and a bright front edge. We investigated the relationship between coronal dimming, filament eruption, and early CME propagation in this rarely seen case. We employed 3D filament and CME shock reconstructions along with estimations of early CME evolution inferred from the associated expansion of the coronal dimming. We performed 3D reconstructions using data from Solar Orbiter, Solar TErrestrial RElations Observatory (STEREO-A), and Solar Dynamics Observatory (SDO) to analyse the path, height, and kinematics of the erupting filament. We developed the ATLAS-3D (Advanced Technique for single Line-of-sight Acquisition of Structures in 3D) method and validated it by comparing it to traditional approaches to reconstructing filament loops and the CME shock structure. ATLAS-3D uses Solar Orbiter data exclusively and integrates existing 3D filament reconstructions from the early stages of the event to establish spatial relationships between the filament and the CME frontal edge. Additionally, we employed the DIRECD method to estimate the characteristics of early CME propagation based on its coronal dimming evolution. The filament height increased from 28 to 616 Mm (0.04 to 0.89 $ R_ sun $) over 30 minutes, from 11:05 to 11:35 UT, with a peak velocity of $648 \ km s $ and a peak acceleration of $1624 \ m s $. At 11:45 UT, the filament deflected by about 12$^ reaching a height of 841 Mm (1.21 $ R_ sun $). Simultaneously, the quasi-spherical CME shock expanded from 383 to 837 Mm (0.55 to 1.2 $ R_ sun $) between 11:25 and 11:35 UT. Over 10 minutes, the distance between the filament apex and the CME leading edge more than doubled, from approximately 93 to 212 Mm (0.13 to 0.3 $ R_ sun $),demonstrating significant growth and increasing separation between them. Key parameters estimated from DIRECD and the 3D filament reconstructions include the CME direction (inclined by $6^ from radial expansion), a half-width of $21^ and a cone height of 1.12 $ R_ sun $, which was derived at the end of the dimming's impulsive phase. The reconstructed 3D CME cone, which represents the inner part of the CME,\ closely matches the observed filament shape at 11:45 UT in terms of both height and angular width. Validation with white-light coronagraph data confirmed the accuracy of the 3D cone, particularly in terms of filament and CME characteristics, including projections to STEREO-A COR2 times. The eruptive event on March 28, 2022, showed rapid filament development and its subsequent deflection from the primary propagation direction. This confirms that connections between dimming and CME expansion can be established by the end of the dimming's impulsive phase, preceding the filament’s deflection at 11:45 UT, illustrating further self-similar CME evolution. Our approach links the expanding dimming with the early CME development, highlighting dimmings as indicators and the DIRECD method's utility in correlating the 2D dimming with 3D CME structure. These findings provide valuable insights into early CME evolution and demonstrate the importance of using multi-viewpoint observations and novel reconstruction methods in space weather forecasting.

Post-outburst and Nebular Phase Spectra of the Fe ii-type Nova V378 Serpentis

Infrared and optical spectra are presented for the nova V378 Serpentis from 28 and 103 days after maximum light. The earlier spectrum, from the post-outburst phase, displays strong lines of N i, moderate lines of C i, and the signature Fe ii lines. He i features are just emerging and the MWIR region is dominated by H i emission. The later spectrum captures a moment in the nebular phase through which many Fe ii novae pass characterized by the strong forbidden lines [N ii] 0.5755 μm and [O ii] 0.7319, 0.7329 μm. Modeling with the photoionization code CLOUDY indicates these lines arise throughout much of the emission line gas despite densities exceeding 1 × 108 cm−3. Other results from the modeling include estimates for the temperature of the nova remnant (4.0–5.0 × 104 K) and ejected mass (2.2 × 10−5 M ☉).

Exploring the Magnetic and Thermal Evolution of a Coronal Jet

Coronal jets are the captivating eruptions that are often found in the solar atmosphere and primarily formed due to magnetic reconnection. Despite their short-lived nature and lower energy compared to many other eruptive events, e.g., flares and coronal mass ejections, they play an important role in heating the corona and accelerating charged particles. However, their generation in the ambience of nonstandard flare regime is not fully understood, and warrant a deeper investigation, in terms of their onset, growth, eruption processes, and thermodynamic evolution. Toward this goal, this paper reports the results of a data-constrained three-dimensional magnetohydrodynamics (MHD) simulation of an eruptive jet; initialized with a non-force-free-field (NFFF) extrapolation and carried out in the spirit of implicit large eddy simulation (ILES). The simulation focuses on the magnetic and dynamical properties of the jet during its onset, and eruption phases, that occurred on 2015 February 5 in an active region NOAA AR12280, associated with a seemingly three-ribbon structure. In order to correlate its thermal evolution with computed energetics, the simulation results are compared with differential emission measurement analysis in the vicinity of the jet. Importantly, this combined approach provides an insight to the onset of reconnection in transients in terms of emission and the corresponding electric current profiles from MHD evolutions. The presented study captures the intricate topological dynamics, finds a close correspondence between the magnetic and thermal evolution in and around the jet location. Overall, it enriches the understanding of the thermal evolution due to MHD processes, which is one of the broader aspects to reveal the coronal heating problem.

The State of Solar Wind Heavy Ions in Interplanetary Coronal Mass Ejection–Driven Geomagnetic Storms

During geomagnetic storms, which are the primary periods for heavy ions from the solar wind to enter Earth’s magnetospheric space, the charge state of solar wind heavy ions during these storms has significant implications for studying the distribution and effects of heavy ions in the magnetosphere. We analyzed the states and variations of heavy ions during 158 interplanetary coronal mass ejection (ICME)–driven geomagnetic storm events using data from the Advanced Composition Explorer satellite and examined four of these events in detail. We found that the increase in the average charge state of heavy ions such as O, Mg, Si, and Fe is positively correlated with the intensity of the geomagnetic storm. Regarding the abundance ratio of heavy ions such as Ne, Mg, Si, and Fe relative to oxygen ions, the rate and magnitude of increase in abundance ratios during extreme geomagnetic storms (Kp = 9) triggered by ICME events are significantly higher than those during other levels of geomagnetic storms. Additionally, we observed that although the average charge states of heavy ions such as O and Fe are correlated with the geomagnetic storm intensity induced by ICMEs, there are significant individual differences in the charge state variations of heavy ions.

Revisiting the Superstorm on 6–7 April 2000 Caused by an Extraordinary Corotating Interaction Region (With an Embedded Coronal Jet?)

AbstractThe 6–7 April 2000 superstorm of SYM‐H intensity = −319 nT discussed in Meng et al. (2019; https://doi.org/10.1029/2018JA026425) was misidentified as being due to an interplanetary coronal mass ejection associated with a solar flare. The interplanetary cause was a highly unusual corotating interaction region (CIR) bounded by a strong fast forward shock (FS) with magnetosonic Mach number Mms = 4.6 and a fast reverse shock (RS) with Mms = 1.9. The exceptionally strong FS caused a ∼3‐factor interplanetary magnetic field (IMF) magnitude amplification in the leading half of the CIR with peak southward IMF Bz = −27 nT causing the superstorm. A plasma region between a tangential discontinuity and the stream interface had a scale size of ∼0.096 AU. We hypothesize that this is the first detection of a coronal jet at 1 AU. The jet/Gold magnetic tongue (1959; https://doi.org/10.1029/JZ064i011p01665) was embedded within the CIR, contained the southward Bz and caused the magnetic storm. We hypothesize that a shrinking coronal hole and magnetic reconnection caused the formation and release of the jet.

Magnetospheric response on impact of solar wind diamagnetic structures borne by eruptive prominence

We address the sequence of Sun-to-Earth phenomena, that enables to study the mechanism for geoefficiency of eruptive prominences propagating from the Sun inside coronal mass ejections (CMEs). An eruptive prominence ejected in the solar wind (SW) moves at the SW velocity Earthward like adiamagnetic structure of eruptive prominence (DSEP).The key feature of the latter is a largesharp plasma concentration jump N inside the DSEP at a simultaneous sharp drop in the interplanetary magnetic field (IMF) modulus B. It is the anti-correlation between the N and B profiles in DSEP, due to which its contact with the magnetosphere may lead not only to magnetosphere compression, but also to penetration of DSEP substance into the magnetosphere. The duration of the magnetospheric disturbance (in the form of dayside auroras), global increase in the current systems, charged particle flux enhancement in the radiation belts, and generation of the irregular Pi2-3 oscillations aredetermined by the DSEP size. We present statistical investigations into DSEPs observed in different years of solar activity and builta qualitative modelfor DSEP geoefficiency.

Chronopharmacotherapy and correction of central pressure in the aorta, structural and functional state of the left ventricular in patients with arterial hypertension and ischemic stroke

Objective. To evaluate the dynamics of central aortic pressure and the cardioprotective effect of antihypertensive chronopharmacotherapy in patients with arterial hypertension (AH) and ischemic stroke. Materials and methods. The study included 119 patients with AH who has suffered an ischemic stroke; patients were randomized in 2 groups depending on the chronopharmacotherapy option: group 1 (n = 60) – patients who received indapamide retard 1.5 mg and valsartan 160 mg in the morning; group 2 (n = 59) – indapamide retard 1.5 mg in the morning and valsartan 80 mg each in the morning and before bedtime. After 2 months of pharmacotherapy, the achievement of the target level of blood pressure was assessed. In group 1, blood pressure was recorded in 47 (78.3 %), in group 2 – in 56 (94.9 %) patients (p < 0.05). The rest of the respondents, who did not reach the blood pressure target, underwent correction of antihypertensive therapy and were excluded from further follow-up. Accordingly, further follow-up was carried out in 47 patients of group 1 (group 1a) and 56 patients of group 2 (group 2a). Initially and after 12 months of therapy, echocardiography parameters ("ALOKA SSD 2500", Japan), as well as daily blood pressure monitoring with determination of central aortic pressure (Peter Telegin LLC BPLabVasotens, Russia) were performed. The results of the study were processed using the Statistica 12.0 program (StatSoftInc, USA). Results. At the time of inclusion in the study, the main parameters of the central aortic pressure and echocardiography parameters in both groups of patients were equivalent. After 12 months a statistically more significant decrease in the main parameters of the central aortic pressure (average daily systolic and diastolic pressure in the aorta, pulse pressure in the aorta, augmentation index in the aorta, amplification of pulse pressure, duration of the expulsion period, subendocardial blood flow efficiency index), as well as echocardiography indicators was recorded in group 2a (end-systolic and end-diastolic dimensions, thickness of the interventricular septum, thickness of the posterior wall of the left ventricular myocardium, left ventricular myocardial mass, left ventricular myocardial mass index and ejection fraction) (p < 0.05). The left ventricular myocardial geometry normalized during therapy was recorded significantly more often in group 2a than in group 1a (p < 0.05). Conclusion. Two times a day intake of valsartan with thiazidelike diuretic in the morning facilitated more significant improvement of central aortic pressure, echocardiography parameters and as well as an improvement in the geometry of the left ventricular myocardium comparing to just morning intake.

Development of a compact forage harvester equipped with a stem length orienter and rectangular deflector for small farms

The object of the study is the technological processes of high-quality crushing of stem feeds, due to the oriented feeding of stems into the grinding chamber and transportation of the crushed mass through a rectangular deflector. A review of the literature sources has shown that at present, the design and technological scheme of a small-sized forage harvester has not yet been developed, which in turn ensures high-quality crushing of stem feeds and reduces operating costs in small farms. As a result of theoretical studies, analytical expressions were obtained to determine the mass velocity at the deflector outlet and the range of mass ejection in the horizontal section. The combine productivity when mowing alfalfa was equal to 6.22 t/h, the range of mass ejection in the horizontal direction was within 7.5...8.0 m (theoretical value – 7.8 m), the average size of crushed particles was 32.89 mm (estimated length – 33.5 mm), the difference between theoretical and actual values is 1.5 %. The results of laboratory and field tests showed the efficiency of the forage harvester, the reliability of the analytical expressions obtained and the efficiency of the stem length orienter was determined. A distinctive feature of the research results is that a design and technological scheme of a small-sized forage harvester equipped with an orienter and a theoretical description of the feed transportation process through a rectangular deflector were developed. According to the presented design and technological scheme, the deflector and orienter have a simplified design and good quality of crushing stem feeds. All this proves the practical significance and applicability of the developed forage harvester

A type II radio burst associated with solar filament–filament interaction

Aims. Solar radio type II bursts are often associated with coronal shocks driven by solar eruptions. In this study, we report a type II burst associated with filament–filament interaction. Methods. Combining the high-quality multiwavelength observations from CHASE, SDO, STEREO, and CALLISTO, we conducted a detailed study of the type II burst associated with filament–filament interaction. Results. On 2023 September 11, an erupting filament (F1) likely disturbed a nearby long filament (F2), causing F2 to subsequently erupt. As a result of possible magnetic reconnection between ejective materials from the two filaments, loop-like structures formed perpendicular to them. Subsequently, the expansion of these loop-like structures triggered a strong coronal mass ejection (CME). Interestingly, a type II burst appeared on the solar spectrum around the time when the loop-like structures formed and the CME appeared above the occulting disk of STEREO/COR1. By converting the frequency of the type II burst to the coronal height using polarization brightness data recorded by the COR1 coronagraph and the spherically symmetric polynomial approximation technique, we determined the formation height of the type II burst to be around 1.45 R⊙, with a speed of approximately 440 km s−1. This is comparable to the observed height of the CME (∼1.43 R⊙), although slightly lower in speed (540 km s−1). Conclusions. All these results indicate that the type II burst was closely associated with filament–filament interactions and was possibly excited by the accompanying CME at the flank. We suggest that the filament–filament interactions played an important role in producing the type II burst by acting as a piston to trigger a strong CME.

A Possible Formation Scenario of the Gaia BH1: Inner Binary Merger in Triple Systems

Based on astrometric measurements and spectral analysis from Gaia DR3, two quiescent black hole (BH) binaries, Gaia BH1 and BH2, have been identified. Their origins remain controversial, particularly for Gaia BH1. By considering a rapidly rotating (ω/ω crit = 0.8) and strongly magnetized (B 0 = 5000 G) merger product, we find that, at typical Galactic metallicity, the merger product can undergo efficient chemically homogeneous evolution. This results in the merger product having a significantly smaller radius during its evolution compared to that of a normally evolving massive star. Under the condition that the initial triple stability is satisfied, we use the Multiple Stellar Evolution code and the MESA code to identify an initial hierarchical triple that can evolve into Gaia BH1. It initially consists of three stars with masses of 9.03 M ⊙, 3.12 M ⊙, and 1 M ⊙, with inner and outer orbital periods of 2.21 days and 121.92 days, and inner and outer eccentricities of 0.41 and 0.45, respectively. This triple initially experiences triple evolution dynamics instability (TEDI) followed by Roche lobe overflow (RLOF). During RLOF, the inner orbit shrinks, and tidal effects gradually suppress the TEDI. Eventually, the inner binary undergoes a merger through contact (or collision). Finally, using models of rapidly rotating and strongly magnetic stars, along with standard core-collapse supernova (SN) or failed supernova (FSN) models, we find that a postmerger binary (PMB) consisting of an 12.11 M ⊙ merger product and a 1 M ⊙ companion star (originally an outer tertiary) can avoid RLOF. After an SN or FSN with a low ejected mass of ∼0.22 M ⊙ and a low kick velocity ( 46−33+25kms−1 or 9−8+16kms−1 ), the PMB can form Gaia BH1 in the Galactic disk.

Unexpected major geomagnetic storm caused by faint eruption of a solar trans-equatorial flux rope

Some geomagnetic storms’ solar origins are ambiguous, making them hard to predict. On March 23, 2023, a severe geomagnetic storm occurred, however, forecasts based on remote-sensing observations failed to predict it. Here, we show clear evidence that this storm originates from the eruption of a trans-equatorial, longitudinal and low-density magnetic flux rope (FR) with weaker coronal emission and no chromospheric signs. The FR’s gentle eruption results in a faint full-halo coronal mass ejection (CME), which is missed by forecasters and not included in CME catalogs. Combining magnetic field modeling and in-situ measurements, we reveal the FR’s southward axial magnetic field as the main cause of the geomagnetic storm. This CME is the stealthiest one reported causing a severe geomagnetic storm. Our study highlights that erupting trans-equatorial FRs can generate major geomagnetic storms in a stealthy way. Characteristic observational signatures of similar eruptions are proposed to help in future forecasts.

How Does the Critical Torus Instability Height Vary with the Solar Cycle?

The ideal magnetohydrodynamic torus instability can drive the eruption of coronal mass ejections. The critical threshold of magnetic field strength decay for the onset of the torus instability occurs at different heights in different solar active regions, and understanding this variation could therefore improve space weather prediction. In this work, we aim to find out how the critical torus instability height evolves throughout the solar activity cycle. We study a significant subset of Helioseismic and Magnetic Imager (HMI) and Michelson Doppler Imager Space-Weather HMI Active Region Patches (SHARPs and SMARPs) from 1996 to 2023, totaling 21,584 magnetograms from 4436 unique active-region patches. For each magnetogram, we compute the critical height averaged across the main polarity inversion line, the total unsigned magnetic flux, and the separation between the positive and negative magnetic polarities. We find the critical height in active regions varies with the solar cycle, with higher (lower) average critical heights observed around solar maximum (minimum). We conclude that this is because the critical height is proportional to the separation between opposite magnetic polarities, which in turn is proportional to the total magnetic flux in a region, and more magnetic regions with larger fluxes and larger sizes are observed at solar maximum. This result is noteworthy because, despite the higher critical heights, more coronal mass ejections are observed around solar maximum than at solar minimum.

Geoelectric fields and geomagnetically induced currents during the April 23–24, 2023 geomagnetic storm

We present a study on the dynamical variations of geoelectric fields E during the intense geomagnetic storm of April 23–24, 2023. The storm is caused by the interplanetary counterpart of a coronal mass ejection erupted from the Sun in association with an M1.7 X-ray flare. The GeoElectric Dynamic Mapping (GEDMap) code is applied to develop spatial E maps using magnetometer data from 29 observatories distributed across northern Europe. The code has been applied during local nighttime and morningtime intense substorms which occurred during the storm main phase. The maps show intensifications and strong variability of the E-fields during the substorm events. In particular, the morningtime event is associated with a significant variability in the E-field direction. Using the computed E-fields, we determined geomagnetically induced currents (GICs) at the sub-auroral station Mäntsälä. The modeled GIC values exhibit significant correlation (correlation coefficients r=0.73−0.76\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r=0.73-0.76$$\\end{document}) with the observed values. The performed E-field mapping provides a basis for the further determination of GICs in selected locations not covered by magnetometers and can be useful in understanding the GIC variability during magnetic storms and substorms.