We present an investigation of partial filament eruption on 2012 June 17 in the active region NOAA 11504. For the first time, we observed the vertical splitting process during the partial eruption with high-resolution narrowband images at 10830 Å. The active filament was rooted in a small δ-sunspot of the active region. Particularly, it underwent the partial eruption in three steps, i.e., the precursor, the first eruption, and the second eruption, while the latter two were associated with a C1.0 flare and a C3.9 flare, respectively. During the precursor, slow magnetic reconnection took place between the filament and the adjoining loops that also rooted in the δ-sunspot. The continuous reconnection not only caused the filament to split into three groups of threads vertically but also formed a new filament, which was growing and accompanied brightening took place around the site. Subsequently, the growing filament erupted together with one group splitted threads, resulted in the first eruption. At the beginning of the first eruption, a subsequent magnetic reconnection occurred between the erupting splitted threads and another ambient magnetic loop. After about 3 minutes, the second eruption occurred as a result of the eruption of two larger unstable filaments induced by the magnetic reconnection. The high-resolution observation provides a direct evidence that magnetic reconnection between filament and its ambient magnetic fields could induce the vertical splitting of the filament, resulting in partial eruption.

A magnetic flux rope (FR), hosting hot plasma, is thought to be central to the physics of coronal mass ejections. Such FRs are widely observed with passbands of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory that are sensitive to emission from the hot plasma around 10 MK. In contrast, observations of warmer (around 1 MK) counterparts of FRs are sparse. In this study, we report the failed eruption of a multithermal FR, hosting both hot and warm plasma. On 2015 May 1, a hot channel appeared in the AIA high-temperature passbands out of the southeastern solar limb to the south of a nearby flare, and then erupted outward. During the eruption, it rotated perpendicular to the erupting direction. The hot channel stopped erupting, and disappeared gradually, showing a failed eruption. During the hot channel eruption, a warm channel appeared sequentially in the AIA low-temperature passbands. It underwent a similar evolution, including the failed eruption, rotation, and disappearance, to the hot channel. A bright compression front is formed in front of the warm channel eruption in AIA low-temperature images. Under the hot and warm channel eruptions, a small flare occurred, upon which several current sheets, connecting the erupting channels and the underneath flare, formed in the AIA high-temperature passbands. Investigating the spatial and temporal relation between the hot and warm channels, we suggest that both channels twist together, constituting the same multithermal FR that has plasma with the high and low temperatures.

Coronal mass ejections (CMEs) result from eruptions of magnetic flux ropes (MFRs) and can possess a three-part structure in white-light coronagraphs, including a bright front, dark cavity, and bright core. In traditional opinion, the bright front forms due to the plasma pileup along the MFR border, the cavity represents the cross section of the MFR, and the bright core corresponds to the erupted prominence. However, this explanation on the nature of the three-part structure is being challenged. In this paper, we report an intriguing event that occurred on 2014 June 14 that was recorded by multiple space- and ground-based instruments seamlessly, clearly showing that the CME front originates from the plasma pileup along the magnetic arcades overlying the MFR, and the core corresponds to a hot-channel MFR. Thus the dark cavity is not an MFR; instead it is a low-density zone between the CME front and a trailing MFR. These observations are consistent with a new explanation on the CME structure. If the new explanation is correct, most (if not all) CMEs should exhibit the three-part appearance in their early eruption stage. To examine this prediction, we make a survey of all CMEs in 2011 and find that all limb events have the three-part feature in the low corona, regardless of their appearances in the high corona. Our studies suggest that the three-part structure is the intrinsic structure of CMEs, which has fundamental importance for understanding CMEs.

Both observations and simulations suggest that the solar filament eruption is closely related to magnetic flux emergence. It is thought that the eruption is triggered by magnetic reconnection between the filament and the emerging flux. However, the details of such a reconnection are rarely presented. In this study, we report the detailed reconnection between a filament and its nearby emerging fields, which led to the reconfiguration and subsequent partial eruption of the filament located over the polarity inversion line of active region 12816. Before the reconnection, we observed repeated brightenings in the filament at a location that overlies a site of magnetic flux cancellation. Plasmoids form at this brightening region, and propagate bidirectionally along the filament. These indicate the tether-cutting reconnection that results in the formation and eruption of a flux rope. To the northwest of the filament, magnetic fields emerge, and reconnect with the context ones, resulting in repeated jets. Afterwards, other magnetic fields emerge near the northwestern filament endpoints, and reconnect with the filament, forming the newly reconnected filament and loops. A current sheet repeatedly occurs at the interface, with the mean temperature and emission measure of 1.7 MK and 1.1×1028 cm−5. Plasmoids form in the current sheet, and propagate along it and further along the newly reconnected filament and loops. The newly reconnected filament then erupts, while the unreconnected filament remains stable. We propose that besides the orientation of emerging fields, some other parameters, such as the position, distance, strength, and area, are also crucial for triggering the filament eruption.

The composition of interplanetary coronal mass ejections (ICMEs), including the ionic charge states and elemental abundances of heavy elements, is tightly correlated with their source regions and eruption processes. This can help in analyzing the eruption mechanisms and plasma origins of CMEs, and deepen our understanding of energetic solar activities. The active regions and quiet-Sun regions have different physical properties; thus, from a statistical point of view, ICMEs originating from the two types of regions should exhibit different compositional characteristics. To demonstrate the differences comprehensively, we conduct survey studies on the ionic charge states of five elements (Mg, Fe, Si, C, and O) and the relative abundances of six elements (Mg/O, Fe/O, Si/O, C/O, Ne/O, and He/O) within ICMEs from 1998 February to 2011 August using data from the Advanced Composition Explorer. The results show that ICMEs from active regions have higher ionic charge states and relative abundances than those from quiet-Sun regions. For the active-region ICMEs, we further analyze the relations between their composition and flare class, and find a positive relationship between them, i.e., the higher the classes of the associated flares, the larger the means of the ionic charge states and relative abundances (except the C/O) within ICMEs. As more (less) fractions of ICMEs originate from active regions around the solar maximum (minimum), and active-region ICMEs usually are associated with higher-class flares, our studies might answer why the composition of ICMEs measured near 1 au exhibits a solar cycle dependence.

Previous survey studies reported that coronal mass ejections (CMEs) can exhibit various structures in white-light coronagraphs, and ∼30% of them have the typical three-part feature in the high corona (e.g., 2–6 R ⊙), which has been taken as the prototypical structure of CMEs. It is widely accepted that CMEs result from eruption of magnetic flux ropes (MFRs), and the three-part structure can be understood easily by means of the MFR eruption. It is interesting and significant to answer why only ∼30% of CMEs have the three-part feature in previous studies. Here we conduct a synthesis of the CME structure in the field of view (FOV) of K-Coronagraph (1.05–3 R ⊙). In total, 369 CMEs are observed from 2013 September to 2022 November. After inspecting the CMEs one by one through joint observations of the Atmospheric Imaging Assembly, K-Coronagraph, and LASCO/C2, we find 71 events according to the criteria: (1) limb event; (2) normal CME, i.e., angular width ≥30°; (3) K-Coronagraph caught the early eruption stage. All (or more than 90% considering several ambiguous events) of the 71 CMEs exhibit the three-part feature in the FOV of K-Coronagraph, while only 30%–40% have the feature in the C2 FOV (2–6 R ⊙). For the first time, our studies show that 90%–100% and 30%–40% of normal CMEs possess the three-part structure in the low and high corona, respectively, which demonstrates that many CMEs can lose the three-part feature during their early evolutions, and strongly supports that most (if not all) CMEs have the MFR structures.

How structures, e.g., magnetic loops, in the upper atmosphere, i.e., the transition region and corona, are heated and sustained is one of the major unresolved issues in solar and stellar physics. Various theoretical and observational studies on the heating of coronal loops have been undertaken. The heating of quiescent loops caused by eruptions, however, is rarely observed. In this study, employing data from the Solar Dynamics Observatory (SDO) and Solar Upper Transition Region Imager (SUTRI), we report the heating of quiescent loops associated with nearby eruptions. In active regions (ARs) 13092 and 13093, a long filament and a short filament, and their overlying loops, were observed on 2022 September 4. In AR 13093, a warm channel erupted toward the northeast, whose material moved along its axis toward the northwest under the long filament, turned to the west above the long filament, and divided into two branches falling to the solar surface. Subsequently, the short filament erupted toward the southeast. Associated with these two eruptions, the quiescent loops overlying the long filament appeared in SDO/Atmospheric Imaging Assembly (AIA) high-temperature images, indicating the heating of loops. During the heating, the signature of magnetic reconnection between loops is identified, including the inflowing motions of loops, and the formation of X-type structures and newly reconnected loops. The heated loops then cooled down. They appeared sequentially in AIA and SUTRI lower-temperature images. All the results suggest that the quiescent loops are heated by reconnection between loops caused by the nearby warm channel and filament eruptions.