Coronal Mass Ejections Eruption Research Articles

Is It Possible to Detect Coronal Mass Ejections on Solar-type Stars through Extreme-ultraviolet Spectral Observations?

Stellar coronal mass ejections (CMEs) from host stars are an important factor that affects the habitability of exoplanets. Although their solar counterparts have been well observed for decades, it is still very difficult to find solid evidence of stellar CMEs. Using the spectral line profile asymmetry caused by the Doppler shift of erupting plasma, several stellar CME candidates have been identified from spectral lines formed at chromospheric or transition region temperatures of the stars. However, a successful detection of stellar CME signals based on the profile asymmetries of coronal lines is still lacking. It is unclear whether we can detect such signals. Here we construct an analytical model for CMEs on solar-type stars and derive an expression of stellar extreme-ultraviolet (EUV) line profiles during CME eruptions. For different instrumental parameters, exposure times, CME propagation directions, and stellar activity levels, we synthesized the corresponding line profiles of Fe ix λ171.07 and Fe xv λ284.16. Further investigations provide constraints on the instrumental requirements for successful detection and characterization of stellar CMEs. Our results show that it is possible to detect stellar CME signals and infer their velocities based on spectral profile asymmetries using an EUV spectrometer with a moderate spectral resolution and signal-to-noise ratio. Our work provides important references for the design of future EUV spectrometers for stellar CME detection and the development of observation strategies.

Unveiling the journey of a highly inclined CME

Context. A fast (∼2000 km s−1) and wide (> 110°) coronal mass ejection (CME) erupted from the Sun on March 13, 2012. Its interplanetary counterpart was detected in situ two days later by STEREO-A and near-Earth spacecraft, such as ACE, Wind, and Cluster. We suggest that at 1 au the CME extended at least 110° in longitude, with Earth crossing its east flank and STEREO-A crossing its west flank. Despite their separation, measurements from both positions showed very similar in situ CME signatures. The solar source region where the CME erupted was surrounded by three coronal holes (CHs). Their locations with respect to the CME launch site were east (negative polarity), southwest (positive polarity) and west (positive polarity). The solar magnetic field polarity of the area covered by each CH matches that observed at 1 au in situ. Suprathermal electrons at each location showed mixed signatures with only some intervals presenting clear counterstreaming flows as the CME transits both locations. The strahl population coming from the shortest magnetic connection of the structure to the Sun showed more intensity. Aims. The aim of this work is to understand the propagation and evolution of the CME and its interaction with the surrounding CHs, to explain the similarities and differences between the observations at each spacecraft, and report what one of the most longitudinal expanded CME structures measured in situ would be. Methods. Known properties of the large-scale structures from a variety of catalogues and previous studies were used to have a better overview of this particular event. In addition, multipoint observations were used to reconstruct the 3D geometry of the CME and determine the context of the solar and heliospheric conditions before the CME eruption and during its propagation. The graduated cylindrical shell model (GCS) was used to reproduce the orientation, size and speed of the structure with a simple geometry. Also, the Drag-Based Model (DBM) was utilised to understand the conditions of the interplanetary medium better in terms of the drag undergone by the structure while propagating in different directions. Finally, a comparative analysis of the different regions of the structure through the different observatories was carried out in order to directly compare the in situ plasma and magnetic field properties at each location. Results. The study presents important findings regarding the in situ measured CME on March 15, 2012, detected at a longitudinal separation of 110° in the ecliptic plane despite its initial inclination being around 45° when erupted (March 13). This suggests that the CME may have deformed and/or rotated, allowing it to be observed near its legs with spacecraft at a separation angle greater than 100°. The CME structure interacted with high-speed streams generated by the surrounding CHs. The piled-up plasma in the sheath region exhibited an unexpected correlation in magnetic field strength despite the large separation in longitude. In situ observations reveal that at both locations there was a flank encounter – where the spacecraft crossed the first part of the CME – then encountered ambient solar wind, and finally passed near the legs of the structure. Conclusions. A scenario covering all evidence is proposed for both locations with a general view of the whole structure and solar wind conditions. Also, the study shows the necessity of having multipoint observations of large-scale structures in the heliosphere.

3D MHD Time-dependent Charge State Ionization and Recombination Modeling of the Bastille Day Coronal Mass Ejection

Heavy ion signatures of coronal mass ejections (CMEs) indicate that rapid and strong heating takes place during the eruption and early stages of propagation. However, the nature of the heating that produces the highly ionized charge states often observed in situ is not fully constrained. An MHD simulation of the Bastille Day CME serves as a test bed to examine the origin and conditions of the formation of heavy ions evolving within the CME in connection with those observed during its passage at L1. In particular, we investigate the bimodal nature of the Fe charge state distribution, which is a quintessential heavy ion signature of CME substructure, as well as the source of the highly ionized plasma. We find that the main heating experienced by the tracked plasma structures linked to the ion signatures examined is due to field-aligned thermal conduction via shocked plasma at the CME front. Moreover, the bimodal Fe distributions can be generated through significant heating and rapid cooling of prominence material. However, although significant heating was achieved, the highest ionization stages of Fe ions observed in situ were not reproduced. In addition, the carbon and oxygen charge state distributions were not well replicated owing to anomalous heavy ion dropouts observed throughout the ejecta. Overall, the results indicate that additional ionization is needed to match observation. An important driver of ionization could come from suprathermal electrons, such as those produced via Fermi acceleration during reconnection, suggesting that the process is critical to the development and extended heating of extreme CME eruptions, like the Bastille Day CME.

A type II solar radio burst without a coronal mass ejection

Context. The Sun produces the most powerful explosions in the Solar System, solar flares, which can also be accompanied by large eruptions of magnetised plasma, coronal mass ejections (CMEs). These processes can accelerate electron beams up to relativistic energies through magnetic reconnection processes during solar flares and CME-driven shocks. Energetic electron beams can in turn generate radio bursts through the plasma emission mechanism. CME shocks, in particular, are usually associated with type II solar radio bursts. Aims. However, on a few occasions, type II bursts have been reported to occur either in the absence of CMEs or shown to be more likely related with the flaring process. It is currently an open question as to how a shock generating type II bursts forms without the occurrence of a CME eruption. Here, we aim to determine the physical mechanism responsible for a type II burst that occurs in the absence of a CME. Methods. By using radio imaging from the Nançay Radioheliograph, combined with observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory spacecraft, we investigate the origin of a type II radio burst that appears to have no temporal association with a white-light CME. Results. We identify a typical type II radio burst with band-split structure that is associated with a C-class solar flare. The type II burst source is located above the flaring active region and ahead of disturbed coronal loops observed in extreme-ultraviolet (EUV) images. The type II burst is also preceded by type III radio bursts, some of which are in fact J bursts, indicating that accelerated electron beams do not all escape along open field lines. The type II sources show single-frequency movement towards the flaring active region. The type II burst is located ahead of a faint EUV front propagating through the corona. Conclusions. Since there is no CME detection, a shock wave is most likely generated by the flaring process or the bulk plasma motions associated with a failed eruption. The EUV front observed is likely a freely propagating wave that expands into surrounding regions. The EUV front propagates at an initial speed of approximately 450 km s−1 and it is likely to steepen into a shock wave in a region of low Alfvén speed as determined from magneto-hydrodynamic modelling of the corona.

Recent progress on understanding coronal mass ejection/flare onset by a NASA living with a star focused science team

We present a report of recent progress on the topic of understanding solar coronal mass ejection (CME) onset from both modeling and observational viewpoints, as carried out from 2019 to the present by the NASA Living with a Star Focused Science Topic team on “Understanding the Onset of Major Solar Eruptions.” Following the typical Focused Science Topic paradigm, a number of research groups were selected and joined together to tackle this problem. The work being carried out by this team explores the role of topology and of helicity transport in creating an environment favorable to CME eruption and in then providing the energy required for CME onset. The team investigated CME energization and initiation via photospheric shearing, via flux rope formation, and via magnetic flux emergence. This article will highlight recent progress made by six American research groups working in these areas. We do not intend to present an exhaustive review of these topics, but rather summarize the ideas from these research groups regarding ongoing and upcoming challenges to the questions of how, when, and why coronal mass ejections erupt from the sun.

Multi-point study of the energy release and impulsive CME dynamics in an eruptive C7 flare

Context. The energy release in eruptive flares and the kinematics of the associated coronal mass ejections (CMEs) are interlinked and require favorable observing positions as both on-disk and off–limb signatures are necessary to characterize these events. Aims. We combine observations from different vantage points to perform a detailed study of a long duration eruptive C7 class flare that occurred on 17 April 2021 and was partially occulted from Earth view. The dynamics and thermal properties of the flare-related plasma flows, the flaring arcade, and the energy releases and particle acceleration are studied together with the kinematic evolution of the associated CME in order to place this long duration event in context of previous eruptive flare studies. Methods. We use data from the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter to analyze the spectral characteristics, timing, and spatial distribution of the flare X-ray emission. Data from the Extreme Ultraviolet Imager (EUVI) onboard the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft are used for context images as well as to track the ejected plasma close to the Sun. With Atmospheric Imaging Assembly extreme ultraviolet (EUV) images from the Solar Dynamics Observatory, the flare is observed off–limb and differential emission measure maps are reconstructed. The coronagraphs onboard STEREO-A are used to track the CME out to around 8 R⊙. Results. The flare showed hard X-ray (HXR) bursts over the duration of an hour in two phases lasting from 16:04 UT to 17:05 UT. During the first phase, a strong increase in emission from hot plasma and impulsive acceleration of the CME was observed. The CME acceleration profile shows a three-part evolution of slow rise, acceleration, and propagation in line with the first STIX HXR burst phase, which is triggered by a rising hot (14 MK) plasmoid. During the CME acceleration phase, we find signatures of ongoing magnetic reconnection behind the erupting structure, in agreement with the standard eruptive flare scenario. The subsequent HXR bursts that occur about 30 min after the primary CME acceleration show a spectral hardening (from δ ≈ 7 to δ ≈ 4) but do not correspond to further CME acceleration and chromospheric evaporation. Therefore, the CME-flare feedback relationship may only be of significance within the first 25 min. of the event under study, as thereafter the flare and the CME eruption evolve independently of each other.

Quantitative Characterization of Magnetic Flux Rope Properties for Two Solar Eruption Events

In order to bridge the gap between heliospheric and solar observations of coronal mass ejections (CMEs), one of the key steps is to improve the understanding of their corresponding magnetic structures like the magnetic flux ropes (MFRs). But it remains a challenge to confirm the existence of a coherent MFR before or upon the CME eruption on the Sun and to quantitatively characterize the CME-MFR due to the lack of direct magnetic field measurements in the corona. In this study, we investigate MFR structures originating from two active regions (ARs), AR 11719 and AR 12158, and estimate their magnetic properties quantitatively. We perform nonlinear force-free field extrapolations with preprocessed photospheric vector magnetograms. In addition, remote-sensing observations are employed to find indirect evidence of MFRs on the Sun and to analyze the time evolution of magnetic reconnection flux associated with the flare ribbons during the eruption. A coherent “preexisting” MFR structure prior to the flare eruption is identified quantitatively for one event from the combined analysis of the extrapolation and observation. Then the characteristics of MFRs for two events on the Sun before and during the eruption forming the CME-MFR, including the axial magnetic flux, field line twist, and reconnection flux, are estimated and compared with the corresponding in situ modeling results. We find that the magnetic reconnection associated with the accompanying flares for both events injects a significant amount of flux into the erupted CME-MFRs.

Modelling a multi-spacecraft coronal mass ejection encounter with EUHFORIA

Context. Coronal mass ejections (CMEs) are a manifestation of the Sun’s eruptive nature. They can have a great impact on Earth, but also on human activity in space and on the ground. Therefore, modelling their evolution as they propagate through interplanetary space is essential. Aims. EUropean Heliospheric FORecasting Information Asset (EUHFORIA) is a data-driven, physics-based model, tracing the evolution of CMEs through background solar wind conditions. It employs a spheromak flux rope, which provides it with the advantage of reconstructing the internal magnetic field configuration of CMEs. This is something that is not included in the simpler cone CME model used so far for space weather forecasting. This work aims at assessing the spheromak CME model included in EUHFORIA. Methods. We employed the spheromak CME model to reconstruct a well observed CME and compare model output to in situ observations. We focus on an eruption from 6 January 2013 that was encountered by two radially aligned spacecraft, Venus Express and STEREO-A. We first analysed the observed properties of the source of this CME eruption and we extracted the CME properties as it lifted off from the Sun. Using this information, we set up EUHFORIA runs to model the event. Results. The model predicts arrival times from half to a full day ahead of the in situ observed ones, but within errors established from similar studies. In the modelling domain, the CME appears to be propagating primarily southward, which is in accordance with white-light images of the CME eruption close to the Sun. Conclusions. In order to get the observed magnetic field topology, we aimed at selecting a spheromak rotation angle for which the axis of symmetry of the spheromak is perpendicular to the direction of the polarity inversion line (PIL). The modelled magnetic field profiles, their amplitude, arrival times, and sheath region length are all affected by the choice of radius of the modelled spheromak.

The Inhomogeneity of Composition Along the Magnetic Cloud Axis

Coronal mass ejections (CMEs) are one of the most energetic explosions in the solar system. It is generally accepted that CMEs result from eruptions of magnetic flux ropes, which are dubbed as magnetic clouds (MCs) in interplanetary space. The composition (including the ionic charge states and elemental abundances) is determined prior to and/or during CME eruptions in the solar atmosphere and does not alter during MC propagation to 1 AU and beyond. It has been known that the composition is not uniform within a cross section perpendicular to the MC axis, and the distribution of ionic charge states within a cross section provides us an important clue to investigate the formation and eruption processes of flux ropes due to the freeze-in effect. The flux rope is a three-dimensional magnetic structure intrinsically, and it remains unclear whether the composition is uniform along the flux rope axis as most MCs are only detected by one spacecraft. In this study, we report an MC that was observed by Advanced Composition Explorer at ∼1 AU during March 4–6, 1998, and Ulysses at ∼5.4 AU during March 24–28, 1998, sequentially. At these times, both spacecraft were located around the ecliptic plane, and the latitudinal and longitudinal separations between them were ∼2.2° and ∼5.5°, respectively. It provides us an excellent opportunity to explore the axial inhomogeneity of flux rope composition, as both spacecraft almost intersected the cloud center at different sites along its axis. Our study shows that the average values of ionic charge states exhibit significant difference along the axis for carbon, and the differences are relatively slight but still obvious for charge states of oxygen and iron as well as the elemental abundances of iron and helium. Besides the means, the composition profiles within the cloud measured by both spacecraft also exhibit some discrepancies. We conclude that the inhomogeneity of composition exists along the cloud axis.

Multiple Sources of Solar High-energy Protons

Abstract During the 24th solar cycle, the Fermi Large Area Telescope (LAT) has observed a total of 27 solar flares possessing delayed γ-ray emission, including the exceptionally well-observed flare and coronal mass ejection (CME) on 2017 September 10. Based on the Fermi/LAT data, we plot, for the first time, maps of possible sources of the delayed >100 MeV γ-ray emission of the 2017 September 10 event. The long-lasting γ-ray emission is localized under the CME core. The γ-ray spectrum exhibits intermittent changes in time, implying that more than one source of high-energy protons was formed during the flare–CME eruption. We find a good statistical correlation between the γ-ray fluences of the Fermi/LAT-observed delayed events and the products of corresponding CME speed and the square root of the soft X-ray flare magnitude. Data support the idea that both flares and CMEs jointly contribute to the production of subrelativistic and relativistic protons near the Sun.

The Magnetic Environment of a Stealth Coronal Mass Ejection

Abstract Interest in stealth coronal mass ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as extreme-ultraviolet dimmings and post-eruptive arcades are hard to identify and require extensive image processing techniques. These weak observational signatures mean that little is currently understood about the physics of these events. We present an extensive study of the magnetic field configuration in which the stealth CME of 2011 March 3 occurred. Three distinct episodes of flare ribbon formation are observed in the stealth CME source active region (AR). Two occurred prior to the eruption and suggest the occurrence of magnetic reconnection that builds the structure that will become eruptive. The third occurs in a time close to the eruption of a cavity that is observed in STEREO-B 171 Å data; this subsequently becomes part of the propagating CME observed in coronagraph data. We use both local (Cartesian) and global (spherical) models of the coronal magnetic field, which are complemented and verified by the observational analysis. We find evidence of a coronal null point, with field lines computed from its neighborhood connecting the stealth CME source region to two ARs in the northern hemisphere. We conclude that reconnection at the null point aids the eruption of the stealth CME by removing the field that acted to stabilize the preeruptive structure. This stealth CME, despite its weak signatures, has the main characteristics of other CMEs, and its eruption is driven by similar mechanisms.

Statistical analysis of characteristics of classified type II radio bursts and their associated solar energetic particle events

In this paper, we investigate 273 type II radio burst events detected by Wind, STEREO spacecraft from January 2010 to March 2018 during the 24th solar cycle. We classify all events as five groups or sub-types according to their starting and ending frequencies, and then analyze the observed characteristics of each group of type II radio bursts and the correlation between the occurrence of solar energetic particle (SEP) events and the associated coronal mass ejection (CME) or type II radio bursts. What we find is as follows. 1) In each group of type II radio burst events, the CME speed (<i>v</i>), width (WD), mass (<i>m</i>), and kinetic energy (<i>E</i><sub>k</sub>) associated with SEP events are generally greater than those with no SEP events, indicating that the generation of SEP events requires a fast and wide energetic CME eruption. 2) Compared with type II radio bursts starting from the DH band, type II radio bursts starting from the metric band have a higher proportion of large SEP events. Multi-band type II radio bursts are more likely to produce SEP events than single-band events, where M-DH-KM type II bursts have the highest proportion of SEP events (73%), and the DH IIs only have the lowest one (19%). 3) In each kind of type II radio bursts, the type IIs with SEP events usually have higher starting frequencies (lower shock forming heights), lower ending frequencies (higher ending heights) and longer durations than those with no SEP events; coronal shock waves that are easy to produce SEP events (especially large SEP events) generally begin to form at a lower height (such as < 3<i>R</i><sub>s</sub>, <i>R</i><sub>s</sub>: solar radius), and are sustained to a much larger height (such as > 30<i>R</i><sub>s</sub>). 4) There exists a strong negative correlation between the duration and the ending frequency of type II radio burst (<i>cc</i> = –0.93). The proportion of SEP events increases with the increase of the duration of type II radio burst, and decreases with the increase of the ending frequency, which largely depends on the CME speed and other properties. The results of this paper further show that the generation of SEP events is greatly related to the sub-types and characteristics of type II radio bursts. The higher the starting frequencies and the lower the ending frequencies of type II radio bursts, such as M-DH-KM type II bursts, of which the CME drives to forming shock waves at a very low height and propagates to a very large height, the longer the duration of the shock, the longer the time it takes to accelerate the particles, and the greater the probability of SEP events (especially large SEP events) is.

Study of Long-Duration Flares and Associated Chromospheric and Coronal Ejections in Solar Cycles 23 and 24

A statistical study of long-duration (long-duration event, LDE) flares in the soft X-ray (SXR) range for solar cycles 23 and 24 is carried out. Graphs of the dependence of the strength of LDE flares and coronal mass ejections (CMEs) on the duration of these flares are constructed. As a result, we find that a significant proportion of LDE flares is not associated with large mass CMEs. This contradicts the hypothesis that the energy required to maintain the post-eruptive phase of LDE flares is supplied by the energy of settling matter after CME eruption. However, most flares are accompanied by mini-eruptions, which may have a significance in the energy balance of LDEs. The diagram of the strength–duration of flares shows that there is a limit of energy and maximum strength of an LDE flare in the SXR range in LDE events. Apparently, this limit differs for cycles 23 and 24. This fact may indicate that there is a limit to the maximum flare energy that can be observed in a particular solar cycle.

A statistical study of plasmoids associated with a post-CME current sheet

Context. Coronal mass ejections (CMEs) are often observed to be accompanied by flare, current sheets, and plasmoids/plasma blobs. 2D and 3D numerical simulations and observations reported plasmoids moving upward as well as downward along the current sheet. Aims. We aim to investigate the properties of plasmoids observed in the current sheet formed after an X-8.3 flare and followed by a fast CME eruption on September 10, 2017 using extreme-ultraviolet (EUV) and white-light coronagraph images. The main goal is to understand the evolution of plasmoids in different spatio-temporal scales using existing ground- and space-based instruments. Methods. We identified the plasmoids manually and tracked them along the current sheet in the successive images of Atmospheric Imaging Assembly (AIA) taken at the 131 Å pass band and in running difference images of the white-light coronagraphs, K-Cor and LASCO/C2. The location and size of the plasmoids in each image were recorded and analyzed, covering the current sheet from the inner to outer corona. Results. We find that the observed current sheet has an Alfvén Mach number of 0.018−0.35. The fast reconnection is also accompanied by plasmoids moving upward and downward. We identified 20 downward-moving and 16 upward-moving plasmoids using AIA 131 Å images. In white-light coronagraph images, only upward-moving plasmoids are observed. Our analysis shows that the downward-moving plasmoids have an average width of 5.92 Mm, whereas upward-moving blobs have an average size of 5.65 Mm in the AIA field of view (FOV). The upward-moving plasmoids, when observed in the white-light images, have an average width of 64 Mm in the K-Cor, which evolves to a mean width of 510 Mm in the LASCO/C2 FOV. Upon tracking the plasmoids in successive images, we find that downward- and upward-moving plasmoids have average speeds of ∼272 km s−1 and ∼191 km s−1, respectively in the EUV channels of observation. The average speed of plasmoids increases to ∼671 km s−1 and ∼1080 km s−1 in the K-Cor and LASCO/C2 FOVs, respectively, implying that the plasmoids become super-Alfvénic when they propagate outward. The downward-moving plasmoids show an acceleration in the range of −11 km s−1 to over 8 km s−1. We also find that the null point of the current sheet is located at ≈1.15 R⊙, where bidirectional plasmoid motion is observed. Conclusions. The width distribution of plasmoids formed during the reconnection process is governed by a power law with an index of −1.12. Unlike previous studies, there is no difference in trend for small- and large-scale plasmoids. The evolution of width W of the plasmoids moving at an average speed V along the current sheet is governed by an empirical relation: V = 115.69W0.37. The presence of accelerating plasmoids near the neutral point indicates a longer diffusion region as predicted by MHD models.

Electron acceleration and radio emission following the early interaction of two coronal mass ejections

Context. Coronal mass ejections (CMEs) are large eruptions of magnetised plasma from the Sun that are often accompanied by solar radio bursts produced by accelerated electrons. Aims. A powerful source for accelerating electron beams are CME-driven shocks, however, there are other mechanisms capable of accelerating electrons during a CME eruption. So far, studies have relied on the traditional classification of solar radio bursts into five groups (Type I–V) based mainly on their shapes and characteristics in dynamic spectra. Here, we aim to determine the origin of moving radio bursts associated with a CME that do not fit into the present classification of the solar radio emission. Methods. By using radio imaging from the Nançay Radioheliograph, combined with observations from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, and Solar Terrestrial Relations Observatory spacecraft, we investigate the moving radio bursts accompanying two subsequent CMEs on 22 May 2013. We use three-dimensional reconstructions of the two associated CME eruptions to show the possible origin of the observed radio emission. Results. We identified three moving radio bursts at unusually high altitudes in the corona that are located at the northern CME flank and move outwards synchronously with the CME. The radio bursts correspond to fine-structured emission in dynamic spectra with durations of ∼1 s, and they may show forward or reverse frequency drifts. Since the CME expands closely following an earlier CME, a low coronal CME–CME interaction is likely responsible for the observed radio emission. Conclusions. For the first time, we report the existence of new types of short duration bursts, which are signatures of electron beams accelerated at the CME flank. Two subsequent CMEs originating from the same region and propagating in similar directions provide a complex configuration of the ambient magnetic field and favourable conditions for the creation of collapsing magnetic traps. These traps are formed if a CME-driven wave, such as a shock wave, is likely to intersect surrounding magnetic field lines twice. Electrons will thus be further accelerated at the mirror points created at these intersections and eventually escape to produce bursts of plasma emission with forward and reverse drifts.

Particle Acceleration and Transport during 3D CME Eruptions

Abstract We calculate particle acceleration during coronal mass ejection (CME) eruptions using combined magnetohydrodynamic and test-particle models. The 2.5D/3D CMEs are generated via the breakout mechanism. In this scenario a reconnection at the “breakout” current sheet (CS) above the flux rope initiates the CME eruption by destabilizing a quasi-static force balance. Reconnection at the flare CS below the erupting flux rope drives the fast acceleration of the CME, which forms flare loops below and produces the energetic particles observed in flares. For test-particle simulations, two times are selected during the impulsive and decay phases of the eruption. Particles are revealed to be accelerated more efficiently in the flare CS rather than in the breakout CS even in the presence of large magnetic islands. Particles are first accelerated in the CSs (with or without magnetic islands) by the reconnection electric field mainly through particle curvature drift. We find, as expected, that accelerated particles precipitate into the chromosphere, become trapped in the loop top by magnetic mirrors, or escape to interplanetary space along open field lines. Some trapped particles are reaccelerated, either via reinjection to the flare CS or through a local Betatron-type acceleration associated with compression of the magnetic field. The energetic particles produce relatively hard energy spectra during the impulsive phase. During the gradual phase, the relaxation of magnetic field shear reduces the guiding field in the flare CS, which leads to a decrease in particle energization efficiency. Important implications of our results for observations of particle acceleration in the solar coronal jets are also discussed.

Extended radio emission associated with a breakout eruption from the back side of the Sun

Context. Coronal mass ejections (CMEs) on the Sun are the largest explosions in the Solar System that can drive powerful plasma shocks. The eruptions, shocks, and other processes associated to CMEs are efficient particle accelerators and the accelerated electrons in particular can produce radio bursts through the plasma emission mechanism. Aims. Coronal mass ejections and associated radio bursts have been well studied in cases where the CME originates close to the solar limb or within the frontside disc. Here, we study the radio emission associated with a CME eruption on the back side of the Sun on 22 July 2012. Methods. Using radio imaging from the Nançay Radioheliograph, spectroscopic data from the Nançay Decametric Array, and extreme-ultraviolet observations from the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory spacecraft, we determine the nature of the observed radio emission as well as the location and propagation of the CME. Results. We show that the observed low-intensity radio emission corresponds to a type II radio burst or a short-duration type IV radio burst associated with a CME eruption due to breakout reconnection on the back side of the Sun, as suggested by the pre-eruptive magnetic field configuration. The radio emission consists of a large, extended structure, initially located ahead of the CME, that corresponds to various electron acceleration locations. Conclusions. The observations presented here are consistent with the breakout model of CME eruptions. The extended radio emission coincides with the location of the current sheet and quasi-separatrix boundary of the CME flux and the overlying helmet streamer and also with that of a large shock expected to form ahead of the CME in this configuration.

Eruption of Prominences Triggered by Coronal Rain in the Solar Atmosphere Observed by SDO/AIA and Stereo/EUVI

The triggering process for coronal mass ejections (CME) in the solar atmosphere is not fully understood. We use observations from different spacecraft at several wavelengths to detect an instability process for a prominence/filament with a subsequent eruption of CME. Time series of spectral lines at 304, 171, 193, and 211 {\AA} have been obtained with the SDO spacecraft, and at 304, 171, 195, and 284 {\AA} with the STEREO spacecraft. A prominence/filament system was observed during November 8-23, 2011, at different angles by SDO, STEREO_A, and STEREO_B. The observations show that a giant tornado began to develop near the base of the prominence at 20:00 UT on November 20, which later caused the appearance of droplets of coronal rain (at 16:00 UT, November 21) which fell downward from the main mass of the prominence. The coronal rain continued until 20:20 UT, November 22, and caused instability of the prominence, after which a CME took place at 22:30 UT on November 22. We assume that the loss of mass owing to coronal rain may lead to instability of prominences and their subsequent eruption. Observations of coronal rain falling from the main part of the mass of prominences could be used for predicting space weather.

New data-driven method of simulating coronal mass ejections

Context. Coronal mass ejections (CMEs) are large eruptions of plasma and magnetic field from the Sun’s corona. Understanding the evolution of the CME is important to evaluate its impact on space weather. Using numerical simulation, we are able to reproduce the occurrence and evolution process of the CME. Aims. The aim of this paper is to provide a new data-driven method to mimic the coronal mass ejections. By using this method, we can investigate the phsical mechanisms of the flux rope formation and the cause of the CME eruption near the real background. Methods. Starting from a potential magnetic field extrapolation, we have solved a full set of magnetohydrodynamic (MHD) equations by using the conservation element and solution element (CESE) numerical method. The bottom boundary is driven by the vector magnetograms obtained from SDO/HMI and vector velocity maps derived from DAVE4VM method. Results. We present a three-dimensional numerical MHD data-driven model for the simulation of the CME that occurred on 2015 June 22 in the active region NOAA 12371. The numerical results show two elbow-shaped loops formed above the polarity inversion line (PIL), which is similar to the tether-cutting picture previously proposed. The temporal evolutions of magnetic flux show that the sunspots underwent cancellation and flux emergence. The signature of velocity field derived from the tracked magnetograms indicates the persistent shear and converging motions along the PIL. The simulation shows that two elbow-shaped loops were reconnected and formed an inverse S-shaped sigmoid, suggesting the occurrence of the tether-cutting reconnection, which was supported by observations of the Atmospheric Imaging Assembly (AIA) telescope. Analysis of the decline rate of the magnetic field indicates that the flux rope reached a region where the torus instability was triggered. Conclusions. We conclude that the eruption of this CME was caused by multiple factors, such as photosphere motions, reconnection, and torus instability. Moreover, our simulation successfully reproduced the three-component structures of typical CMEs.

The Role of a Magnetic Topology Skeleton in a Solar Active Region

Abstract We investigate the 3D magnetic topology in the active region NOAA 11719 nine hours before and after a flare–coronal mass ejection (CME) event on 2013 April 11. The extrapolated 3D coronal magnetic field is computed employing a boundary integrated model, and a complex magnetic topology skeleton comprising five fairly robust null points and their relevant structures are revealed with a mathematical method based on a Poincaré index of isolated 3D null points. Comparative analyses show that the magnetic topology skeleton in this active region determines geometries of post-flare loops and flare ribbons, and characterizes the initial stage of the CME. The present work demonstrates that the magnetic topology skeleton plays an important role in the process of the flare–CME eruption.