Formation of a streamer blob via the merger of multiple plasma clumps below 2Rs

Context. Propagating streamer blobs could be an important source of disturbances in the solar wind. Direct observations on formation of streamer blobs could be a proxy for understanding the formation of small-scale structures and disturbances in the solar wind. Aims. We aim to investigate how a streamer blob is formed before it is observed in the outer corona. Methods. Usingspecialcoordinated-observationsfromSOHO/LASCO,GOES/SUVIandSDO/AIA, we study the precursors of a streamer blob as seen in the corona below 2.0 solar radii (Rs). Results. We found that the streamer blob was formed due to the gradual merging of three clumps of brightenings initiated from the lower corona at about 1.8Rs, which is likely driven by expansion of the loop system at the base of the streamer. The acceleration of the blob starts from 1.9Rs or lower. It propagates along the south flank of the streamer where an expanding elongated brightening occurs coincidently. Conclusions. Our observations demonstrate that formation of a streamer blob is a complex process. We suggest that the expansion of the loop results in a pinching-off flux-rope-like blob at the loop apex below 2Rs. When the blob moves outward, it can be transferred across the overlying loops through interchange/component magnetic reconnection and then is released into the open field system. When the blob moves toward open field lines, interchange magnetic reconnections might also occur, and that can accelerate the plasma blob intermittently whilst allow it to transfer across the open field lines. Such dynamics in a streamer blob might further trigger small-scale disturbances in the solar wind such as switchbacks in the inner heliosphere

An extreme-ultraviolet wave associated with the possible expansion of sheared arcades

Context. Solar extreme-ultraviolet (EUV) waves are propagating disturbances in the corona, and they are usually accompanied with various solar eruptions, from large-scale coronal mass ejections to small-scale coronal jets. Aims. Generally, it is believed that EUV waves are driven by the rapid expansion of coronal loops overlying the erupting cores. In this paper, we present an exception of an EUV wave that was not triggered by the expansion of coronal loops overlying the erupting core. Methods. Combining the multiwavelength observations from multiple instruments, we studied the event in detail. Results. The eruption was restricted in the active region (AR) and disturbed the nearby sheared arcades (SAs) connecting the source AR to a remote AR. Interestingly, following the disturbance, an EUV wave formed close to the SAs, but far away from the eruption source. Conclusions. All the results show that the EUV wave had a closer temporal and spatial relationship with the disappearing part of SAs than the confined eruption. Hence, we suggest that the EUV wave was likely triggered by the expansion of some strands of SAs, rather than the expansion of erupting loops. It can be a possible complement for the driving mechanisms of EUV waves

Electron Densities of Transition Region Loops Derived from IRIS O iv Spectral Data

Loops are fundamental structures in the magnetized atmosphere of the Sun. Their physical properties are crucial for understanding the nature of the solar atmosphere. Transition region loops are relatively dynamic and their physical properties have not yet been fully understood. With spectral data of the line pair of O iv 1399.8 Å and 1401.2 Å ( ${T}_{\max }=1.4\times {10}^{5}$ K) of 23 transition region loops obtained by IRIS, we carry out the first systematic analyses to their loop lengths ( L ), electron densities ( n _e ), and effective temperatures. We found electron densities, loop lengths, and effective temperatures of these loops are in the ranges of 8.9 × 10 ^9 –3.5 × 10 ^11 cm ^−3 , 8–30 Mm, and 1.9 × 10 ^5 –1.3 × 10 ^6 K, respectively. At a significant level of 90%, regression analyses show that the relationship between electron densities and loop lengths is n _e [cm ^−3 ] ∝ ( L [Mm]) ^−0.78±0.42 , while the dependences of electron densities on effective temperatures and that on the line intensities are not obvious. These observations demonstrate that transition region loops are significantly different than their coronal counterparts. Further studies on the theoretical aspect based on the physical parameters obtained here are of significance for understanding the nature of transition region loops

Concurrence of a Kelvin-Helmholtz instability and Kármán vortex street in the Sun’s corona

Context. Instabilities are crucial to understanding the mass transportation and energy transformation in the solar atmosphere. Observations of the concurrence among the Kelvin-Helmholtz instability (KHI) and Kármán vortex street (KVS) in conditions as extreme as the Sun’s corona have yet to be reported. Aims. We aim to find evidence of a concurrence between the KHI and KVS in the Sun’s corona. Methods. We analyzed high-resolution data from Extreme Ultraviolet Imager aboard Solar Orbiter and the Atmospheric Imaging Assembly aboard Solar Dynamics Observatory. Results. Thanks to the high temporal resolution of EUI data, in an interacting region between a jet and coronal plumes, we observed the development of ruffles and breakdown of blobs. The intrinsic parameters of this dynamic system suggest the possibility of both the KHI and KVS occurring in the corona. The observations also show that the coupling of the two instabilities has facilitated the formation of vortices, which may therefore have enhanced the transformation from kinetic energy to thermal energy, as well as mass mixing among systems across magnetic field lines in the Sun’s corona. Conclusions. The present study reports the very first EUI observations of a concurrence of the KHI and KVS and their coupling in the coronal conditions

Internal Activities in a Solar Filament and Heating in Its Threads

Filaments are one of the most common features in the solar atmosphere and are of significance in solar, stellar, and laboratory plasma physics. Using data from the Chinese H α Solar Explorer, the Solar Upper Transition Region Imager, and the Solar Dynamics Observatory, we report on multiwavelength imaging and spectral observations of the activation of a small filament. The filament activation produces several localized dynamic brightenings, which are probably produced by internal reconnections of the braided magnetic fields in the filament. The filament expands during the activation, and its threads reconnect with the ambient magnetic fields, which leads to the formation of hot arcades or loops overlying the filament. The thermal energy of each of these localized brightenings is estimated in the order of 10 ^25 –10 ^27 erg, and the total energy is estimated to be ∼1.77 × 10 ^28 erg. Our observations demonstrate that the internal magnetic reconnections in the filament can lead to localized heating in the filament threads and prompt external reconnections with ambient corona structures and thus could contribute to the energy and mass transferring into the corona

Protective Functions of Liver X Receptor α in Established Vulnerable Plaques: Involvement of Regulating Endoplasmic Reticulum–Mediated Macrophage Apoptosis and Efferocytosis

Background Liver X receptor (LXR) belongs to the metabolic nuclear receptor superfamily, which plays a critical regulatory role in vascular physiology/pathology. However, effects of systemic LXR activation on established vulnerable plaques and the potential isotype‐specific role involved remain unclear. Methods and Results The 8‐week‐old male apolipoprotein E−/− mice went through carotid branch ligation and renal artery constriction, combined with a high‐fat diet. Plaques in the left carotid artery acquired vulnerable features 4 weeks later, confirmed by magnetic resonance imaging scans and histological analysis. From that time on, mice were injected intraperitoneally daily with PBS or GW3965 (10 mg/kg per day) for an additional 4 weeks. Treatment with LXR agonists reduced the lesion volume by 52.61%, compared with the vehicle group. More important, a profile of less intraplaque hemorrhage detection and necrotic core formation was found. These actions collectively attenuated the incidence of plaque rupture. Mechanistically, reduced lesional apoptosis, enhanced efferocytosis, and alleviated endoplasmic reticulum stress are involved in the process. Furthermore, genetic ablation of LXRα, but not LXRβ, blunted the protective effects of LXR on the endoplasmic reticulum stress–elicited C/EBP‐homologous protein pathway in peritoneal macrophages. In concert with the LXRα‐predominant role in vitro, activated LXR failed to stabilize vulnerable plaques and correct the acquired cellular anomalies in LXRα−/− apolipoprotein E−/− mice. Conclusions Our results revealed that LXRα mediates the capacity of LXR activation to stabilize vulnerable plaques and prevent plaque rupture via amelioration of macrophage endoplasmic reticulum stress, lesional apoptosis, and defective efferocytosis. These findings might expand the application scenarios of LXR therapeutics for atherosclerosis