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We report the smallest coronal jets ever observed in the quiet Sun with recent high-resolution observations from the High Resolution Telescopes (HRIEUV and HRILyα ) of the Extreme Ultraviolet Imager on board the Solar Orbiter (SO). In the HRIEUV (174 Å) images, these microjets usually appear as nearly collimated structures with brightenings at their footpoints. Their average lifetime, projected speed, width, and maximum length are 4.6 minutes, 62 km s−1, 1.0 Mm, and 7.7 Mm, respectively. Inverted-Y shaped structures and moving blobs can be identified in some events. A subset of these events also reveal signatures in the HRILyα (H i Lyα at 1216 Å) images and the extreme ultraviolet images taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Our differential emission-measure (EM) analysis suggests a multithermal nature and an average density of ∼1.4 × 109 cm−3 for these microjets. Their thermal and kinetic energies were estimated to be ∼3.9 × 1024 erg and ∼2.9 × 1023 erg, respectively, which are of the same order of the released energy predicted by the nanoflare theory. Most events appear to be located at the edges of network lanes and magnetic flux concentrations, suggesting that these coronal microjets are likely generated by magnetic reconnection between small-scale magnetic loops and the adjacent network field.

Using the data from the Solar Dynamics Observatory, the Ahead of Solar Terrestrial Relations Observatory, the Global Oscillation Network Group (GONG), and the Large Angle and Spectrometric Coronagraphs, the nearly 90° deflected eruption of a filament and the following coronal mass ejection (CME) occurring on the northern edge of AR 11123 on 2010 November 15 were presented in this paper. The filament was very small with the projected length of about 2.6 × 104 km and centered at about W . The potential-field source-surface model identified that the filament was located near the northern flank of a helmet streamer. The filament initially erupted northward to the nearby open fields with speeds from 151 to 336 km s−1, resulting in a B7.6 subflare and some signatures of interchange reconnection. This suggested that the erupting filament interacted with the open fields at first. Then, guided by the highly-inclined open fields, it deflected about 90° southward on the plane of the sky to the magnetic minimum in the streamer configuration. In addition, the CME with the width of 64° and the central position angle of 221° was also deflected obviously in the inner corona to attain its final direction. Because the eruption failed to penetrate the open fields, these results corroborate the idea that open magnetic flux can act as a magnetic wall while a streamer belt can act as a potential well for coronal eruptions in the Sun.

In this paper, we study the onset process of a solar eruption on 21 February 2015, focusing on its unambiguous precursor phase. With multi-wavelength imaging observations from the Atmospheric Imaging Assembly (AIA), definitive tether-cutting (TC) reconnection signatures, i.e., flux convergence and cancellation, bidirectional jets, as well as topology change of hot loops, were clearly observed below the pre-eruption filament. As TC reconnection progressed between the sheared arcades that enveloped the filament, a channel-like magnetic flux rope (MFR) arose in multi-wavelength AIA passbands wrapping around the main axis of the filament. With the subsequent ascent of the newborn MFR, the filament surprisingly split into three branches. After a 7-hour slow rise phase, the high-lying branch containing by the MFR abruptly accelerated causing a two-ribbon flare; while the two low-lying branches remained stable forming a partial eruption. Complemented by kinematic analysis and decay index calculation, we conclude that TC reconnection played a key role in building up the eruptive MFR and triggering its slow rise. The onset of the torus instability may have led the high-lying branch into the standard eruption scenario in the fashion of a catastrophe.

Stellar flares are characterized by sudden enhancement of electromagnetic radiation in stellar atmospheres. So far, much of our understanding of stellar flares has come from photometric observations, from which plasma motions in flare regions could not be detected. From the spectroscopic data of LAMOST DR7, we have found one stellar flare that is characterized by an impulsive increase followed by a gradual decrease in the Hα line intensity on an M4-type star, and the total energy radiated through Hα is estimated to be of the order of 1033 erg. The Hα line appears to have a Voigt profile during the flare, which is likely caused by Stark pressure broadening due to the dramatic increase in electron density and/or opacity broadening due to the occurrence of strong nonthermal heating. Obvious enhancement has been identified in the red wing of the Hα line profile after the impulsive increase in the Hα line intensity. The red-wing enhancement corresponds to plasma moving away from the Earth at a velocity of 100–200 km s−1. According to our current knowledge of solar flares, this red-wing enhancement may originate from: (1) flare-driven coronal rain, (2) chromospheric condensation, or (3) a filament/prominence eruption either with nonradial backward propagation or with strong magnetic suppression. The total mass of the moving plasma is estimated to be of the order of 1015 kg.

We present an observation of the interaction between a filament and the outer spine-like loops that produces a blowout surge within one footpoint of large-scale coronal loops on 2015 February 6. Based the observation of the AIA 304 and 94 Å, the activated filament is initially embedded below a dome of a fan-spine configuration. Due to the ascending motion, the erupting filament reconnects with the outer spine-like field. We note that the material in the filament blows out along the outer spine-like field to form the surge with a wider spire, and a two-ribbon flare appears at the site of the filament eruption. In this process, small bright blobs appear at the interaction region and stream up along the outer spine-like field and down along the eastern fan-like field. As a result, a leg of the filament becomes radial and the material in it erupts, while another leg forms the new closed loops. Our results confirm that the successive reconnection occurring between the erupting filament and the coronal loops may lead to a strong thermal/magnetic pressure imbalance, resulting in a blowout surge.

We study the early evolution of a hot-channel-like magnetic flux rope (MFR) toward eruption. Combining with imaging observation and magnetic field extrapolation, we find that the hot channel possibly originated from a pre-existing seed MFR with a hyperbolic flux tube (HFT). In the precursor phase, three-dimensional tether-cutting reconnection at the HFT is most likely resulting in the heating and buildup of the hot channel. In this process, the forming hot channel was rapidly enlarged at its spatial size and slipped its feet to two remote positions. Afterward, it instantly erupted outwards with an exponential acceleration, leaving two core dimmings near its feet. We suggest that pre-flare reconnection at the HFT played a crucial role in enlarging the seed MFR and facilitating the onset of its final solar eruption. Moreover, a recently predicted drifting of MFR's footpoints was detected at both core dimmings. In particular, we find that MFR's west footpoint drift was induced by a new reconnection geometry among the erupting MFR's leg and thereby inclined arcades. As MFR's west footpoints gradually drifted to a new position, a set of newborn atypical flare loops connected into the west core dimming, causing a rapid decrease of dimmed area inside this core dimming and also generating a secondary flare ribbon at their remote feet. This reveals that core dimmings may suffer a pronounced diminishment due to the eruptive MFR's footpoint drift, implying that mapping the real footpoints of the erupting MFR down to the Sun's surface is more difficult than previously thought.

Using high spatial and temporal data from the New Vacuum Solar Telescope (NVST) and the Solar Dynamics Observatory (SDO), we present unambiguous observations of recurrent two-sided loop jets caused by magnetic reconnection between erupting minifilaments and nearby large filament. The observations demonstrate that three twosided loop jets, which ejected along the large filament in opposite directions, had similar appearance and originated from the same region. We find that a minifilament erupted and drove the first jet. It reformed at the same neutral line later, and then underwent partial and total eruptions, drove the second and third jets, respectively. In the course of the jets, cool plasma was injected into the large filament. Furthermore, persistent magnetic flux cancelation occurred at the neutral line under the minifilament before its eruption and continued until the end of the observation. We infer that magnetic flux cancellation may account for building and then triggering the minifilament to erupt to produce the two-sided loop jets. This observation not only indicates that two-sided loop jets can be driven by minifilament eruptions, but also sheds new light on our understanding of the recurrent mechanism of two-sided loop jets.