Mass Ejections Research Articles

Main-belt comets as contributors to the near-Earth objects population

Aims. Most studies of the dynamics of main-belt objects describing the evolution of the bodies in inner Solar System have been carried with models that include weak nongravitational forces, such as the Yarkovsky and YORP effects. Only about 19 objects exhibit cometary-type activity, with sublimation being the principal mechanism. This paper presents a study of the influence of cometary- type nongravitational forces on the dynamics of main-belt comets, and the possible paths and timescales of evolution into other Solar System regions. Methods. We used the standard Marsden model for cometary-type activity. This model was designed for elongated orbits and the continuous ejection of mass, while the main-belt comets exhibit a different mode of activity. For this reason, we propose a simple model of nongravitational force activation that is consistent with observations. The dynamical evolution of objects was studied using a fifteenth-order RADAU integrator implemented in the REBOUND package. Results. The paper presents the dynamical routes of main-belt comets in the inner Solar System when cometary-type nongravitational forces are included in calculations. The forces significantly shorten the time of transition to other regions compared to the Yarkovsky effect, shortening this time to as little as a few thousand years depending on the frequency of the activity and the A1, A2, and A3 Marsden constants. There is a large probability of a transition to near-Earth object(NEO)-type orbits for bodies with A2 < 0, which means that cometary-type nongravitational forces can be a non-negligible mechanism increasing the number of bodies in that population. The forces can also deliver active main-belt objects into mean motion resonances but can equally eject bodies into outer planetary regions on far shorter timescales than the Yarkovsky and YORP effects. Cometary-type nongravitational effects should be included in dynamical studies of individual sublimating active asteroids.

Convective Magnetic Flux Emergence Simulations from the Deep Solar Interior to the Photosphere: Comprehensive Study of Flux Tube Twist

The emergence of magnetic flux from the deep convection zone plays an important role in solar magnetism, such as the generation of active regions and triggering of various eruptive phenomena, including jets, flares, and coronal mass ejections. To investigate the effects of magnetic twist on flux emergence, we performed numerical simulations of flux tube emergence using the radiative magnetohydrodynamic code R2D2 and conducted a systematic survey on the initial twist. Specifically, we varied the twist of the initial tube both positively and negatively from zero to twice the critical value for kink instability. As a result, regardless of the initial twist, the flux tube was lifted by the convective upflow and reached the photosphere to create sunspots. However, when the twist was too weak, the photospheric flux was quickly diffused and not retained long as coherent sunspots. The degree of magnetic twist measured in the photosphere conserved the original twist relatively well and was comparable to actual solar observations. Even in the untwisted case, a finite amount of magnetic helicity was injected into the upper atmosphere because the background turbulence added helicity. However, when the initial twist exceeded the critical value for kink instability, the magnetic helicity normalized by the total magnetic flux was found to be unreasonably larger than the observations, indicating that the kink instability of the emerging flux tube may not be a likely scenario for the formation of flare-productive active regions.

Direct Observations of a Shock Traversing Preceding Two Coronal Mass Ejections: Insights from Solar Orbiter, Wind, and STEREO Observations

The three successive coronal mass ejections (CMEs) that erupted from 2023 November 27–28, provide the first opportunity to shed light on the entire process of a shock propagating through, sequentially compressing, and modifying two preceding CMEs using in situ data from Solar Orbiter, Wind, and STEREO-A. We describe the interaction of the three CMEs as follows: CME-1 and CME-2 interacted with each other at distances close to the Sun. Subsequently, the shock (S3) driven by CME-3 caught up with and compressed ICME-2 before 0.83 au, forming a typical shock–ICME interaction event observed by the Solar Orbiter. The S3 continued to propagate, crossing ICME-2 and propagating into ICME-1 as observed by Wind, and completely overtaking both ICME-1 and ICME-2 at STEREO-A. The interaction between S3 and the preceding two ICMEs leads to a clear compression of preceding ICMEs including an increase in magnetic field (∼150%) and a reduction in the interval of ICMEs. It presents direct and compelling evidence that a shock can completely traverse two preceding CMEs, accompanied by a significant decrease in shock strength (magnetic compression ratio decrease from 1.74 to 1.49). Even though the three ICMEs interact significantly in the heliosphere, their magnetic field configurations exhibit coherence at different observation points, especially for ICME-3. Those results highlight the significant implications of shock–CME interactions for CME propagation and space weather forecasting.

A Data-driven Magnetohydrodynamic Simulation of the 2011 February 15 Coronal Mass Ejection from Active Region NOAA 11158

We present a boundary data-driven magnetohydrodynamic (MHD) simulation of the 2011 February 15 coronal mass ejection (CME) event of Active Region NOAA 11158. The simulation is driven at the lower boundary with an electric field derived from the normal magnetic field and the vertical electric current measured from the Solar Dynamics Observatory (SDO) Helioseismic Magnetic Imager vector magnetograms. The simulation shows the buildup of a pre-eruption coronal magnetic field that is close to the nonlinear force-free field extrapolation, and it subsequently develops multiple eruptions. The sheared/twisted field lines of the pre-eruption magnetic field show qualitative agreement with the brightening loops in the SDO Atmospheric Imaging Assembly (AIA) hot passband images. We find that the eruption is initiated by the tether-cutting reconnection in a highly sheared field above the central polarity inversion line and a magnetic flux rope with dipped field lines forms during the eruption. The modeled erupting magnetic field evolves to develop a complex structure containing two distinct flux ropes and produces an outgoing double-shell feature consistent with the Solar Terrestrial Relations Observatory B/Extreme UltraViolet Imager observation of the CME. The foot points of the erupting field lines are found to correspond well with the dimming regions seen in the SDO/AIA observation of the event. These agreements suggest that the derived electric field is a promising way to drive MHD simulations to establish the realistic pre-eruption coronal field based on the observed vertical electric current and model its subsequent dynamic eruption.

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.

Investigating the Behavior and Spatiotemporal Variations of Green-line Emission in the Solar Corona

Understanding coronal structure and dynamics can be facilitated by analyzing green-line emission, which enables the investigation of diverse coronal structures such as coronal loops, streamers, coronal holes, and various eruptions in the solar atmosphere. In this study, we investigated the spatiotemporal behaviors of green-line emissions in both low and high latitudes across nine solar cycles, ranging from Solar Cycle 17 to the current Solar Cycle 25, using the modified homogeneous data set. We employed methodologies such as cross correlation, power spectral density, and wavelet transform techniques for this analysis. We found distinct behaviors in green-line energy across various latitudinal distributions in the solar atmosphere. The trends observed at higher latitudes differ from those at lower latitudes. The emission behaviors show a close association with other solar phenomena like solar flares, sunspots, and coronal mass ejections throughout the solar cycles. The observed variations exhibit harmonic periods. The emission activity is significantly higher in the low latitudes, accounting for over 70% of the emissions, while the higher latitudes contribute less than 30%. The emissions exhibit asymmetric behavior between the northern and southern hemispheres, leading to a 44 yr cycle of solar hemispheric dominance shifts. Various factors, such as Alfvén waves, solar magnetic fields, sunspots, differential rotation, and reconnection events, influence the observed differences in behavior between lower and higher latitudes, suggesting the existence of potential underlying phenomena contributing to deviations in properties, intensity, temporal dynamics, and spatiotemporal lifetime.