Coronal Dimming Research Articles

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.

Recovery of coronal dimmings

Recovery of coronal dimmings

Nonparametric Statistics on Magnetic Properties at the Footpoints of Erupting Magnetic Flux Ropes

It is under debate whether the magnetic field in the solar atmosphere carries neutralized electric currents, in particular, whether a magnetic flux rope (MFR), which is considered the core structure of coronal mass ejections, carries neutralized electric currents. Recently Wang et al. (2023) studied magnetic flux and electric current measured at the footpoints of 28 eruptive MFRs from 2010 to 2015. Because of the small sample size, no rigorous statistical analysis has been done. Here, we include nine more events from 2016 to 2023 and perform a series of nonparametric statistical tests at a significance level of 5%. The tests confirm that there exist no significant differences in magnetic properties between conjugated footpoints of the same MFR, which justifies the method of identifying the MFR footpoints through coronal dimming. The tests demonstrate that there exist no significant differences between MFRs with preeruption dimming and those with only posteruption dimming. However, there is a medium level of association between MFRs carrying substantial net current and those producing preeruption dimming, which can be understood by the Lorentz self-force of the current channel. The tests also suggest that in estimating the magnetic twist of MFRs, it is necessary to take into account the spatially inhomogeneous distribution of electric current density and magnetic field.

Coronal dimmings as indicators of the direction of early coronal mass ejection propagation

Context. Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the Sun that can cause severe disturbances in space weather. Earth-directed CMEs are responsible for the disruption of technological systems and damaging power grids. However, the early evolution of CMEs, especially Earth-directed ones, is poorly tracked using traditional coronagraphs along the Sun-Earth line. Aims. The most distinct phenomena associated with CMEs in the low corona are coronal dimmings, which are localized regions of reduced emission in the extreme-ultraviolet (EUV) and soft X-rays formed due to mass loss and expansion during a CME. We present a new approach to estimating the early CME propagation direction based on the expansion of coronal dimmings. Methods. We developed the Dimming InfeRred Estimate of CME Direction (DIRECD) method. First, we performed simulations of CMEs in 3D using a geometric CME cone model and varying parameters such as width, height, source location, and deflection from the radial direction to study their influence on the CME projection onto the solar sphere. Second, we estimated the dominant direction of the dimming extent based on the evolution of the dimming area. Third, using the derived dominant direction of the dimming evolution on the solar sphere, we solved an inverse problem to reconstruct an ensemble of CME cones at different heights, widths, and deflections from the radial propagation. Finally, we searched for which CME parameter combinations the CME orthogonal projections onto the solar sphere would match the geometry of the dimming at the end of its impulsive phase best; we did so to derive the CME direction in 3D. We tested our approach on two case studies on 1 October, 2011 and 6 September, 2011. We also validated our results with 3D tie-pointing of the CME bubble in an EUV low corona and with 3D reconstructions by graduated cylindrical shell modeling (GCS) of white-light CMEs higher up in the corona. Results. Using DIRECD, we found that the CME on 1 October, 2011 expanded dominantly toward the south-east, while the CME on 6 September, 2011 was inclined toward the north-west. This is in agreement with the CME direction estimates from previous studies using multi-viewpoint coronagraphic observations. Conclusions. Our study demonstrates that coronal dimming information can be used to estimate the CME’s direction early in its evolution. This allows us to provide information on the CME direction before it is observed in the coronograph’s field of view, which is of practical importance for space weather forecasting and the mitigation of potential adverse impacts on Earth.

Parameters of Coronal Dimmings and Their Variations during Solar Cycle 24

Parameters of Coronal Dimmings and Their Variations during Solar Cycle 24

Large-scale Coronal Dimming Foreshadowing a Solar Eruption on 2011 October 1

Understanding large-scale solar eruptions requires detailed investigation of the entire system’s evolution, including the magnetic environment enveloping the source region and searches for precursor activity prior to event onset. We combine stereoscopic observations from the Solar Dynamics Observatory (SDO) and STEREO-B spacecraft for several hours before a filament ejection, M1.2-class eruptive flare, and coronal mass ejection (CME) originating in NOAA active region (AR) 11305 on 2011 October 1. Two episodes of significant preeruption coronal dimming that occurred well to the southeast of the ejected filament are identified. The CME subsequently took off with a substantial component of velocity toward the dimming, which became very pronounced during eruption. We used SDO/Helioseismic and Magnetic Imager (HMI) data to reconstruct the magnetic environment of the system and found that it contains a null point near the dimming region. AR 11305 had quite complex connections to nearby ARs 11302 and 11306, as well as to other regions of decayed AR flux. The intensifying and spatially expanding precursor dimming was accompanied by southeastward rising motions of loops toward the null point and northeastward and southwestward motions of loops retracting away. These motions and the dimming are consistent with persistent magnetic reconnection occurring at the null point as it moved upward and southeastward, thereby removing a strapping magnetic field high above AR 11305. Eventually, the filament was ejected explosively toward the null point. We conclude that the breakout model for solar eruptions provides a compelling account of this event. Furthermore, we conjecture that preeruption dimmings may be much more frequent than currently recognized.

Three-dimensional relation between coronal dimming, filament eruption, and CME

Context.Coronal dimmings are localized regions of reduced emission in the extreme-ultraviolet (EUV) and soft X-rays formed as a result of the expansion and mass loss by coronal mass ejections (CMEs) low in the corona. Distinct relations have been established between coronal dimmings (intensity, area, magnetic flux) and key characteristics of the associated CMEs (mass and speed) by combining coronal and coronagraphic observations from different viewpoints in the heliosphere.Aims.We investigate the relation between the spatiotemporal evolution of the dimming region and both the dominant direction of the filament eruption and CME propagation for the 28 October 2021 X1.0 flare/CME event observed from multiple viewpoints in the heliosphere by Solar Orbiter, STEREO-A, SDO, and SOHO.Methods.We present a method for estimating the dominant direction of the dimming development based on the evolution of the dimming area, taking into account the importance of correcting the dimming area estimation by calculating the surface area of a sphere for each pixel. To determine the propagation direction of the flux rope during early CME evolution, we performed 3D reconstructions of the white-light CME by graduated cylindrical shell modeling (GCS) and 3D tie-pointing of the eruptive filament.Results.The dimming evolution starts with a radial expansion and later propagates more to the southeast. The orthogonal projections of the reconstructed height evolution of the prominent leg of the erupting filament onto the solar surface are located in the sector of the dominant dimming growth, while the orthogonal projections of the inner part of the GCS reconstruction align with the total dimming area. The filament reaches a maximum speed of ≈250 km s−1at a height of about ≈180 Mm before it can no longer be reliably followed in the EUV images. Its direction of motion is strongly inclined from the radial direction (64° to the east, 32° to the south). The 3D direction of the CME and the motion of the filament leg differ by 50°. This angle roughly aligns with the CME half-width obtained from the CME reconstruction, suggesting a relation between the reconstructed filament and the associated leg of the CME body.Conclusions.The dominant propagation of the dimming growth reflects the direction of the erupting magnetic structure (filament) low in the solar atmosphere, though the filament evolution is not directly related to the direction of the global CME expansion. At the same time, the overall dimming morphology closely resembles the inner part of the CME reconstruction, validating the use of dimming observations to obtain insight into the CME direction.

Observations of Mini Coronal Dimmings Caused by Small-scale Eruptions in the Quiet Sun

Small-scale eruptions could play an important role in coronal heating, generation of solar energetic particles (SEPs), and mass source of the solar wind. However, they are poorly observed, and their characteristics, distributions, and origins remain unclear. Here a mini coronal dimming was captured by the recently launched Solar Orbiter spacecraft. The observations indicate that a minifilament eruption results in the dimming and takes away approximately (1.65 ± 0.54) × 1013 g of mass, which also exhibits similar features as the sources of SEP events. The released magnetic free energy is of the order of ∼1027 erg. Our results suggest that weak constraining force makes the flux rope associated with the minifilament easily enter a torus-unstable domain. We discuss that weak magnetic constraints from low-altitude background fields may be a general condition for the quiet-Sun eruptions, which provide a possible mechanism for the transport of coronal material and energy from the lower to the middle or even higher corona.

The Merging of a Coronal Dimming and the Southern Polar Coronal Hole

We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hr. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager, which is on board the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer on board Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive the magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of the bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event because the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole.

Investigating Pre-eruptive Magnetic Properties at the Footprints of Erupting Magnetic Flux Ropes

It is well established that solar eruptions are powered by free magnetic energy stored in the current-carrying magnetic field in the corona. It has also been generally accepted that magnetic flux ropes (MFRs) are a critical component of many coronal mass ejections. What remains controversial is whether MFRs are present well before the eruption. Our aim is to identify progenitors of MFRs, and investigate pre-eruptive magnetic properties associated with these progenitors. Here we analyze 28 MFRs erupting within 45° from the disk center from 2010 to 2015. All MFRs’ feet are well identified by conjugate coronal dimmings. We then calculate the magnetic properties at the feet of the MFRs, prior to their eruptions, using Helioseismic and Magnetic Imager vector magnetograms. Our results show that only 8 erupting MFRs are associated with significant nonneutralized electric currents, 4 of which also exhibit pre-eruptive dimmings at the footprints. Twist and current distributions are asymmetric at the two feet of these MFRs. The presence of pre-eruption dimmings associated with nonneutralized currents suggests the preexisting MFRs. Furthermore, the evolution of conjugate dimmings and electric currents within the footprints can provide clues about the internal structure of MFRs and their formation mechanism.

Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun’s early angular momentum evolution. A signal diagnostic of CMEs on the Sun is coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe xii 1349 Å and Fe xxi 1354 Å emission from ϵ Eridani (ϵ Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope’s Cosmic Origins Spectrograph. Following a flare in 2015 February, ϵ Eri’s Fe xxi emission declined by 81 ± 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe xxi decline was the decay of an earlier, unseen flare. Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe xii-emitting (1 MK) plasma to less than a few × 1015 g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on ϵ Eri. On the Sun, 1015 g CMEs occur once every few days. For ϵ Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6 , well below the star’s estimated 30 mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.

Coronal Dimmings Shine Light on Stellar CMEs

Coronal mass ejections from stars have eluded easy observation, so scientists are looking at what’s left behind.

A Study of Dimmings, CMEs, and Flares during the STEREO-SOHO Quadrature

During the quadrature period (2010 December–2011 August) the STEREO-A and B satellites were approximately at right angles to the SOHO satellite. This alignment was particularly advantageous for determining the coronal mass ejection (CME) properties, since the closer a CME propagates to the plane of sky, the smaller the measurement inaccuracies are. Our primary goal was to study dimmings and their relationship to CMEs and flares during this time. We identified 53 coronal dimmings using STEREO/EUVI 195 Å observations, and linked 42 of the dimmings to CMEs (observed with SOHO/LASCO/C2) and 23 to flares. Each dimming in the catalog was processed with the Coronal Dimming Tracker which detects transient dark regions in extreme ultraviolet images directly, without the use of difference images. This approach allowed us to observe footpoint dimmings: the regions of mass depletion at the footpoints of erupting magnetic flux rope structures. Our results show that the CME mass has a linear, moderate correlation with dimming total EUV intensity change, and a monotonic, moderate correlation with dimming area. These results suggest that the more the dimming intensity drops and the larger the erupting region is, the more plasma is evacuated. We also found a strong correlation between the flare duration and the total change in EUV intensity. The correlation between dimming properties showed that larger dimmings tend to be brighter; they go through more intensity loss and generally live longer—supporting the hypothesis that larger transient open regions release more plasma and take longer to close down and refill with plasma.

Coronal Mass Ejections and Dimmings: A Comparative Study Using MHD Simulations and SDO Observations

Abstract Solar coronal dimmings have been observed extensively in recent years. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings as well as their relationship with CMEs. In this study, we investigate coronal dimmings by combining simulation and observational efforts. By utilizing a data-constrained global magnetohydrodynamics model (Alfvén-wave solar model), we simulate coronal dimmings resulting from different CME energetics and flux rope configurations. We synthesize the emissions of different EUV spectral bands/lines and compare with SDO/AIA and EVE observations. A detailed analysis of the simulation and observation data suggests that the transient dimming/brightening are related to plasma heating processes, while the long-lasting core and remote dimmings are caused by mass-loss process induced by the CME. Moreover, the interaction between the erupting flux rope with different orientations and the global solar corona could significantly influence the coronal dimming patterns. Using metrics such as dimming depth and dimming slope, we investigate the relationship between dimmings and CME properties (e.g., CME mass, CME speed) in the simulation. Our result suggests that coronal dimmings encode important information about the associated CMEs, which provides a physical basis for detecting stellar CMEs from distant solar-like stars.

Formation of Magnetic Flux Rope During Solar Eruption. I. Evolution of Toroidal Flux and Reconnection Flux

Magnetic flux ropes (MFRs) constitute the core structure of coronal mass ejections (CMEs), but hot debates remain on whether the MFR forms before or during solar eruptions. Furthermore, how flare reconnection shapes the erupting MFR is still elusive in three dimensions. Here we studied a new MHD simulation of CME initiation by tether-cutting magnetic reconnection in a single magnetic arcade. The simulation follows the whole life, including the birth and subsequent evolution, of an MFR during eruption. In the early phase, the MFR is partially separated from its ambient field by a magnetic quasi-separatrix layer (QSL) that has a double-J shaped footprint on the bottom surface. With the ongoing of the reconnection, the arms of the two J-shaped footprints continually separate from each other, and the hooks of the J shaped footprints expand and eventually become closed almost at the eruption peak time, and thereafter the MFR is fully separated from the un-reconnected field by the QSL. We further studied the evolution of the toroidal flux in the MFR and compared it with that of the reconnected flux. Our simulation reproduced an evolution pattern of increase-to-decrease of the toroidal flux, which is reported recently in observations of variations in flare ribbons and transient coronal dimming. The increase of toroidal flux is owing to the flare reconnection in the early phase that transforms the sheared arcade to twisted field lines, while its decrease is a result of reconnection between field lines in the interior of the MFR in the later phase.

2019 International Women’s Day event

Context. We present a detailed analysis of an eruptive event that occurred on 2019 March 8 in the active region AR 12734, which we refer as the International Women’s Day event. The event under study is intriguing based on several aspects: (1) low-coronal eruptive signatures come in ‘pairs’, namely, there is a double-peaked flare, two coronal dimmings, and two extreme ultraviolet (EUV) waves; (2) although the event is characterized by a complete chain of eruptive signatures, the corresponding coronagraphic signatures are weak; and (3) although the source region of the eruption is located close to the center of the solar disc and the eruption is thus presumably Earth-directed, heliospheric signatures are very weak with very weak Earth impact. Aims. In order to understand the initiation and evolution of this particular event, we performed a comprehensive analysis using a combined observational-modeling approach. Methods. We analyzed a number of multi-spacecraft and multi-instrument (both remote-sensing and in situ) observations, including soft X-ray, EUV, radio and white-light emission, as well as plasma, magnetic field, and particle measurements. We employed 3D nonlinear force-free modeling to investigate the coronal magnetic field configuration in and around the active region, the graduated cylindrical shell model to make a 3D reconstruction of the CME geometry, and the 3D magnetohydrodynamical numerical model EUropean Heliospheric FORecasting Information Asset to model the background state of the heliosphere. Results. Our results reveal a two-stage C1.3 flare, associated with two EUV waves that occur in close succession and two-stage coronal dimmings that evolve co-temporally with the flare and type II and III radio bursts. Despite its small GOES class, a clear drop in magnetic free energy and helicity is observed during the flare. White light observations do not unambiguously indicate two separate CMEs, but rather a single entity most likely composed of two sheared and twisted structures corresponding to the two eruptions observed in the low corona. The corresponding interplanetary signatures are that of a small flux rope swith indications of strong interactions with the ambient plasma, which result in a negligible geomagnetic impact. Conclusions. Our results indicate two subsequent eruptions of two systems of sheared and twisted magnetic fields, which already begin to merge in the upper corona and start to evolve further out as a single entity. The large-scale magnetic field significantly influences both the early and the interplanetary evolution of the structure. During the first eruption, the stability of the overlying field was disrupted, enabling the second eruption. We find that during the propagation in the interplanetary space the large-scale magnetic field, that is, the location of heliospheric current sheet between the AR and the Earth, is likely to influence propagation, along with the evolution of the erupted structure(s).

Determining the source and eruption dynamics of a stealth CME using NLFFF modelling and MHD simulations

Context. Coronal mass ejections (CMEs) that exhibit weak or no eruption signatures in the low corona, known as stealth CMEs, are problematic as upon arrival at Earth they can lead to geomagnetic disturbances that were not predicted by space weather forecasters. Aims. We investigate the origin and eruption of a stealth event that occurred on 2015 January 3 that was responsible for a strong geomagnetic storm upon its arrival at Earth. Methods. To simulate the coronal magnetic field and plasma parameters of the eruption we use a coupled approach. This approach combines an evolutionary nonlinear force-free field model of the global corona with a MHD simulation. Results. The combined simulation approach accurately reproduces the stealth event and suggests that sympathetic eruptions occur. In the combined simulation we found that three flux ropes form and then erupt. The first two flux ropes, which are connected to a large AR complex behind the east limb, erupt first producing two near-simultaneous CMEs. These CMEs are closely followed by a third, weaker flux rope eruption in the simulation that originated between the periphery of AR 12252 and the southern polar coronal hole. The third eruption coincides with a faint coronal dimming, which appears in the SDO/AIA 211 Å observations, that is attributed as the source responsible for the stealth event and later the geomagnetic disturbance at 1 AU. The incorrect interpretation of the stealth event being linked to the occurrence of a single partial halo CME observed by LASCO/C2 is mainly due to the lack of STEREO observations being available at the time of the CMEs. The simulation also shows that the LASCO CME is not a single event but rather two near-simultaneous CMEs. Conclusions. These results show the significance of the coupled data-driven simulation approach in interpreting the eruption and that an operational L5 mission is crucial for space weather forecasting.

Two-Stage Evolution of an Extended C-Class Eruptive Flaring Activity from Sigmoid Active Region NOAA 12734: SDO and Udaipur-CALLISTO Observations

In this article, we present a multi-wavelength investigation of a C-class flaring activity that occurred in the active region NOAA 12734 on 8 March 2019. The investigation utilizes data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) and the Udaipur-CALLISTO solar radio spectrograph of the Physical Research Laboratory. This low intensity C1.3 event is characterized by typical features of a long-duration event (LDE), viz. extended flare arcade, large-scale two-ribbon structures and twin coronal dimmings. The eruptive event occurred in a coronal sigmoid and displayed two distinct stages of energy release, manifested in terms of temporal and spatial evolution. The formation of twin-dimming regions are consistent with the eruption of a large flux rope with footpoints lying in the western and eastern edges of the coronal sigmoid. The metric radio observations obtained from Udaipur-CALLISTO reveals a broad-band ( $\approx50\,\text{--}\,180~\text{MHz}$ ), stationary plasma emission for $\approx7~\text{min}$ during the second stage of the flaring activity that resemble a type IV radio burst. A type III decametre-hectometre radio bursts with starting frequency of $\approx2.5~\text{MHz}$ precedes the stationary type IV burst observed by Udaipur-CALLISTO by $\approx5~\text{min}$ . The synthesis of multi-wavelength observations and non-linear force-free field (NLFFF) coronal modeling together with magnetic decay index analysis suggest that the sigmoid flux rope underwent a zipping-like uprooting from its western to eastern footpoints in response to the overlying asymmetric magnetic field confinement. The asymmetrical eruption of the flux rope also accounts for the observed large-scale structures viz. apparent eastward shift of flare ribbons and post-flare loops along the polarity inversion line (PIL), and provides evidence for lateral progression of magnetic reconnection site as the eruption proceeds.

Indications of stellar coronal mass ejections through coronal dimmings

Coronal mass ejections (CMEs) are huge expulsions of magnetized matter from the Sun and stars, traversing space with speeds of millions of kilometers per hour. Solar CMEs can cause severe space weather disturbances and consumer power outages on Earth, whereas stellar CMEs may even pose a hazard to the habitability of exoplanets. While CMEs ejected by our Sun can be directly imaged by white-light coronagraphs, for stars this is not possible. So far, only a few candidates for stellar CME detections are reported. Here we demonstrate a different approach, based on sudden dimmings in the extreme-ultraviolet (EUV) and X-ray emission caused by the CME mass loss. We report dimming detections associated with flares on cool stars, indicative of stellar CMEs and benchmarked by Sun-as-a-star EUV measurements. This study paves the way for comprehensive detections and characterizations of CMEs on stars, important for planetary habitability and stellar evolution.

From Pseudostreamer Jets to Coronal Mass Ejections: Observations of the Breakout Continuum

Abstract The magnetic breakout model, in which reconnection in the corona leads to destabilization of a filament channel, explains numerous features of eruptive solar events, from small-scale jets to global-scale coronal mass ejections (CMEs). The underlying multipolar topology, pre-eruption activities, and sequence of magnetic-reconnection onsets (first breakout, then flare) of many observed fast CMEs/eruptive flares are fully consistent with the model. Recently, we demonstrated that most observed coronal-hole jets in fan/spine topologies also are induced by breakout reconnection at the null point above a filament channel (with or without a filament). For these two types of eruptions occurring in similar topologies, the key question is, why do some events generate jets while others form CMEs? We focused on the initiation of eruptions in large bright points/small active regions that were located in coronal holes and clearly exhibited null-point (fan/spine) topologies: such configurations are referred to as pseudostreamers. We analyzed and compared Solar Dynamics Observatory/Atmospheric Imaging Assembly, Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment, and Reuven Ramaty High Energy Solar Spectroscopic Imager observations of three events. Our analysis of the events revealed two new observable signatures of breakout reconnection prior to the explosive jet/CME outflows and flare onset: coronal dimming and the opening up of field lines above the breakout current sheet. Most key properties were similar among the selected erupting structures, thereby eliminating region size, photospheric field strength, magnetic configuration, and pre-eruptive evolution as discriminating factors between jets and CMEs. We consider the factors that contribute to the different types of dynamic behavior, and conclude that the main determining factor is the ratio of the magnetic free energy associated with the filament channel compared to the energy associated with the overlying flux inside and outside the pseudostreamer dome.