arXiv subjects

Yuandeng Shen

Publications and source records attributed to Yuandeng Shen.

69 records · Page 4Linked to original sources

arXiv2017

On a solar blowout jet: driven mechanism and the formation of cool and hot components

We present the observations of a blowout jet that experienced two distinct ejection stages. The first stage started from the emergence of a small positive magnetic polarity, which cancelled with the nearby negative magnetic field and caused the rising of a mini-filament and its confining loops. This further resulted in a small jet due to the magnetic reconnection between the rising confining loops and the overlying open field. The second ejection stage was mainly due to the successive removal of the confining field by the reconnection. Thus that the filament erupted and the erupting cool filament material directly combined with the hot jet originated form the reconnection region and therefore formed the cool and hot components of the blowout jet. During the two ejection stages, cool Hα jets are also observed cospatial with their coronal counterparts, but their appearance times are earlier than the hot coronal jets a few minutes. Therefore, the hot coronal jets are possibly caused by the heating of the cool Hα jets, or the rising of the reconnection height from chromosphere to the corona. The scenario that magnetic reconnection occurred between the confining loops and the overlying open loops are supported by many observational facts, including the bright patches on the both sides of the mini-filament, hot plasma blobs along the jet body, and periodic metric radio type III bursts at the very beginnings of the two stages. The evolution and characteristics of these features manifest the detailed non-linear process in the magnetic reconnection.

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arXiv2017

Successive Two-sided loop Jets Caused by Magnetic Reconnection between Two adjacent Filamentary Threads

We present observational analysis of two successive two-sided loop jets observed by the ground-based New Vacuum Solar Telescope (NVST) and the space-borne Solar Dynamics Observatory ( SDO). The two successive two-sided loop jets manifested similar evolution process and both were associated with the interaction of two small-scale adjacent filamentary threads, magnetic emerging and cancellation processes at the jet's source region. High temporal and high spatial resolution observations reveal that the two adjacent ends of the two filamentary threads are rooted in opposite magnetic polarities within the source region. The two threads approached to each other, and then an obvious brightening patch is observed at the interaction position. Subsequently, a pair of hot plasma ejections are observed heading to opposite directions along the paths of the two filamentary threads, and with a typical speed of two-sided loop jets of the order 150 km/s. Close to the end of the second jet, we report the formation of a bright hot loop structure at the source region, which suggests the formation of new loops during the interaction. Based on the observational results, we propose that the observed two-sided loop jets are caused by the magnetic reconnection between the two adjacent filamentary threads, largely different from the previous scenario that a two-sided loop jet is generated by magnetic reconnection between an emerging bipole and the overlying horizontal magnetic fields.

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arXiv2015

Fine Magnetic Structure and Origin of Counter-Streaming Mass Flows in a Quiescent Solar Prominence

We present high-resolution observations of a quiescent solar prominence which was consisted of a vertical and a horizontal foot encircled by an overlying spine, and counter-streaming mass flows were ubiquitous in the prominence. While the horizontal foot and the spine were connecting to the solar surface, the vertical foot was suspended above the solar surface and supported by a semicircular bubble structure. The bubble first collapsed and then reformed at a similar height, finally, it started to oscillate for a long time. We find that the collapsing and oscillation of the bubble boundary were tightly associated with a flare-like feature located at the bottom of the bubble. Based on the observational results, we propose that the prominence should be composed of an overlying horizontal spine encircling a low-lying horizontal and a vertical foot, in which the horizontal foot was consisted of shorter field lines running partially along the spine and with the both ends connecting to the solar surface, while the vertical foot was consisted of piling-up dips due to the sagging of the spine fields and supported by a bipolar magnetic system formed by parasitic polarities (i.e., the bubble). The upflows in the vertical foot were possibly caused by the magnetic reconnection at the separator between the bubble and the overlying dips, which intruded into the persistent downflow field and formed the picture of counter-streaming mass flows. In addition, the counter-streaming flows in the horizontal foot were possibly caused by the imbalanced pressure at the both ends.

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arXiv2014

Simultaneous Transverse Oscillations of a Prominence and a Filament and Longitudinal Oscillation of another Filament Induced by a Single Shock Wave

We present the first stereoscopic and Doppler observations of simultaneous transverse oscillations of a prominence and a filament and longitudinal oscillation of another filament launched by a single shock wave. Using H-alpha Doppler observations, we derive the three-dimensional oscillation velocities at different heights along the prominence axis. The results indicate that the prominence has a larger oscillation amplitude and damping time at higher altitude, but the periods at different heights are the same (i.e., 13.5 minutes). This suggests that the prominence oscillates like a linear vertical rigid body with one end anchored on the Sun. One of the filaments shows weak transverse oscillation after the passing of the shock, which is possibly due to the low altitude of the filament and the weakening (due to reflection) of the shock wave before the interaction. Large amplitude longitudinal oscillation is observed in the other filament after the passing of the shock wave. The velocity amplitude and period are about 26.8 km/s and 80.3 minutes, respectively. We propose that the orientation of a filament or prominence relative to the normal vector of the incoming shock should be an important factor for launching transverse or longitudinal filament oscillations. In addition, the restoring forces of the transverse prominence are most likely due to the coupling of gravity and magnetic tension of the supporting magnetic field, while that for the longitudinal filament oscillation is probably the resultant force of gravity and magnetic pressure.

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arXiv2014

A Chain of Winking (Oscillating) Filaments Triggered by an Invisible Extreme-Ultraviolet Wave

Winking (oscillating) filaments have been observed for many years. However, observations of successive winking filaments in one event have not been reported yet. In this paper, we present the observations of a chain of winking filaments and a subsequent jet that are observed right after the X2.1 are in AR11283. The event also produced an Extreme-ultraviolet (EUV) wave that has two components: upward dome-like wave (850 km/s) and lateral surface wave (554 km/s) which was very weak (or invisible) in imaging observations. By analyzing the temporal and spatial relationships between the oscillating filaments and the EUV waves, we propose that all the winking filaments and the jet were triggered by the weak (or invisible) lateral surface EUV wave. The oscillation of the filaments last for two or three cycles, and their periods, Doppler velocity amplitudes, and damping times are 11 - 22 minutes, 6 - 14 km/s, and 25 - 60 minutes, respectively. We further estimate the radial component magnetic field and the maximum kinetic energy of the filaments, and they are 5 - 10 Gauss and ~ 10^19 J, respectively. The estimated maximum kinetic energy is comparable to the minimum energy of ordinary EUV waves, suggesting that EUV waves can efficiently launch filament oscillations on their path. Based on our analysis results, we conclude that the EUV wave is a good agent for triggering and connecting successive but separated solar activities in the solar atmosphere, and it is also important for producing solar sympathetic eruptions.

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arXiv2014

Successive filament eruptions within one solar breakout event

The magnetic breakout model has been widely used to explain solar eruptive activities. Here, we apply it to explain successive filament eruptions occurred in a quadrupolar magnetic source region. Based on the high temporal and spatial resolution, multi-wavelengths observations taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO), we find some signatures that support the occurrence of breakout-like external reconnection just before the start of the successive filament eruptions. Furthermore, the extrapolated three-dimensional coronal field also reveals that the magnetic topology above the quadrupolar source region resembles that of the breakout model. We propose a possible mechanism within the framework of the breakout model to interpret the successive filament eruptions, in which the so-called magnetic implosion mechanism is firstly introduced to be the physical linkage of successive filament eruptions. We conclude that the structural properties of coronal fields are important for producing successive filament eruptions.

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arXiv2013

Diffraction, Refraction, and Reflection of An Extreme-Ultraviolet Wave Observed during Its Interactions with Remote Active Regions

We present observations of the diffraction, refraction, and reflection of a global extreme-ultraviolet (EUV) wave propagating in the solar corona. These intriguing phenomena are observed when the wave interacts with two remote active regions, and they together exhibit the wave property of this EUV wave. When the wave approached AR11465, it became weaker and finally disappeared in the active region, but a few minutes latter a new wavefront appeared behind the active region, and it was not concentric with the incoming wave. In addition, a reflected wave was also observed simultaneously on the wave incoming side. When the wave approached AR11459, it transmitted through the active region directly and without reflection. The formation of the new wavefront and the transmission could be explained with diffraction and refraction effects, respectively. We propose that the different behaviors observed during the interactions may caused by different speed gradients at the boundaries of the two active regions. For the origin of the EUV wave, we find that it formed ahead of a group of expanding loops a few minutes after the start of the loops' expansion, which represents the initiation of the associated coronal mass ejection (CME). Based on these results, we conclude that the EUV wave should be a nonlinear magnetosonic wave or shock driven by the associated CME, which propagated faster than the ambient fast-mode speed and gradually slowed down to an ordinary linear wave. Our observations support the hybrid model that includes both fast wave and slow non-wave components.

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arXiv2013

SDO/AIA and Hinode/EIS Observations of Interaction Between an EUV Wave and Active Region Loops

We present detailed analysis of an extreme ultraviolet (EUV) wave and its interaction with active region (AR) loops observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Hinode EUV Imaging Spectrometer (EIS). This wave was initiated from AR 11261 on 2011 August 4 and propagated at velocities of 430--910 km\s. It was observed to traverse another AR and cross over a filament channel on its path. The EUV wave perturbed neighboring AR loops and excited a disturbance that propagated toward the footpoints of these loops. EIS observations of AR loops revealed that at the time of the wave transit, the original redshift increased by about 3 km\s, while the original blueshift decreased slightly. After the wave transit, these changes were reversed. When the EUV wave arrived at the boundary of a polar coronal hole, two reflected waves were successively produced and part of them propagated above the solar limb. The first reflected wave above the solar limb encountered a large-scale loop system on its path, and a secondary wave rapidly emerged 144 Mm ahead of it at a higher speed. These findings can be explained in the framework of a fast-mode magnetosonic wave interpretation for EUV waves, in which observed EUV waves are generated by expanding coronal mass ejections.

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arXiv2012

On a Coronal Blowout Jet: The First Observation of a Simultaneously Produced Bubble-like CME and a Jet-like CME in a Solar Event

The coronal blowout jet is a peculiar category among various jet phenomena, of which the sheared base arch, often carrying a small filament, experiences a miniature version of blowout eruption that produces large-scale coronal mass ejection (CME). In this paper, we report such a coronal blowout jet with high-resolution multi-wavelength and multi-angle observations taken from Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Big Bear Solar Observatory. For the first time, we find that a simultaneous bubble-like and a jet-like CMEs were dynamically related to the blowout jet that showed cool and hot components next to each other. Our observational results indicate that: (1) the cool component was resulted from the eruption of the filament contained within the jet's base arch, and it further caused the bubble-like CME; (2) the jet-like CME was associated with the hot component, which was the outward moving heated plasmas generated by the reconnection of the base arch and its ambient open field lines. On the other hand, bifurcation of the jet's cool component was also observed, which was resulted from the uncoupling of the erupting filament's two legs that were highly twisted at the very beginning. Based on these results, we propose a model to interpret the coronal blowout jet, of which the external reconnection not only produces the jet-like CME but also leads to the rising of the filament. Subsequently, internal reconnection starts underneath the rising filament and thereby causes the bubble-like CME.

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arXiv2012

Sympathetic Partial and Full Filament Eruptions Observed in One Solar Breakout Event

We report two sympathetic solar eruptions, including a partial and a full flux rope eruption in a quadrupolar magnetic region, where a large and a small filament resided above the middle and the east neutral lines respectively. The large filament first rose slowly at a speed of 8 km/s for 23 minutes and then it was accelerated to 102 km/s. Finally, this filament erupted successfully and caused a coronal mass ejection. During the slow rising phase, various evidence for breakout-like external reconnection has been identified at high and low temperature lines. The eruption of the small filament started around the end of the large filament's slow rising. This filament erupted partially and no associating coronal mass ejection could be detected. Based on a potential field extrapolation, we find that the topology of the three-dimensional coronal field above the source region is composed of three low-lying lobes and a large overlying flux system, and a null point located between the middle lobe and the overlying antiparallel flux system. We propose a possible mechanism within the framework of the magnetic breakout model to interpret the sympathetic filament eruptions, in which the magnetic implosion mechanism is thought to be a possible linkage between the sympathetic eruptions, and the external reconnection at the null point transfers field lines from the middle lobe to the lateral lobes and thereby leads to the full (partial) eruption of the observed large (small) filament. Other possible mechanisms are also discussed briefly. We conclude that the structural properties of coronal fields are important for producing sympathetic eruptions.

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arXiv2012

Observational Study Of the Quasi-Periodic Fast Propagating Magnetosonic Waves and the Associated Flare on 2011 May 30

On 2011 May 30, quasi-periodic fast propagating (QFP) magnetosonic waves accompanied by a C2.8 flare were directly imaged by the Atomospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. The QFP waves successively emanated from the flare kernel, they propagated along a cluster of open coronal loops with a phase speed of 834 km/s during the flare's rising phase, and the multiple arc-shaped wave trains can be fitted with a series of concentric circles. We generate the k-omega diagram of the Fourier power and find a straight ridge that represents the dispersion relation of the waves. Along the ridge, we find a lot of prominent nodes which represent the available frequencies of the QFP waves. On the other hand, the frequencies of the flare are also obtained by analyzing the flare light curves using the wavelet technique. The results indicate that almost all the main frequencies of the flare are consistent with those of the QFP waves. This suggests that the flare and the QFP waves were possibly excited by a common physical origin. On the other hand, a few low frequencies revealed by the k-omega diagram can not be found in the accompanying flare. We propose that these low frequencies were possibly due to the leakage of the pressure-driven p-mode oscillations from the photosphere into the low corona, which should be a noticeable mechanism for driving the QFP waves observed in the corona.

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arXiv2012

Evidence for the Wave Nature of an Extreme Ultraviolet Wave Observed by the Atmospheric Imaging Assembly Onboard the Solar Dynamics Observatory

Extreme Ultraviolet (EUV) waves have been found for about 15 years. However, significant controversy remains over their physical natures and origins. In this paper, we report an EUV wave that was accompanied by an X1.9 flare and a partial halo coronal mass ejection. Using high temporal and spatial resolution observations taken by the {\em Solar Dynamics Observatory} and the Solar-TErrestrial RElations Observatory, we are able to investigate the detailed kinematics of the EUV wave. We find several arguments that support the fast-mode wave scenario: (1) The speed of the EUV wave (570 km/s) is higher than the sound speed of quiet-Sun corona. (2) Significant deceleration of the EUV wave (-130 m/s2) is found during its propagation. (3) The EUV wave resulted in the oscillations of a loop and a filament along its propagation path, and a reflected wave from the polar coronal hole is also detected. (4) Refraction or reflection effect is observed when the EUV wave was passing through two coronal bright points. (5) The dimming region behind the wavefront stopped to expand when the wavefront started to become diffuse. (6) The profiles of the wavefront exhibited a dispersive nature, and the magnetosonic Mach number of the EUV wave derived from the highest intensity jump is about 1.4. In addition, triangulation indicates that the EUV wave propagated within a height range of about 60-100 Mm above the photosphere. We propose that the EUV wave observed should be a nonlinear fast-mode magnetosonic wave that propagated freely in the corona after it was driven by the CME expanding flanks during the initial period.

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arXiv2012

Simultaneous Observations of a Large-Scale Wave Event in the Solar Atmosphere: From Photosphere to Corona

For the first time, we report a large-scale wave that was observed simultaneously in the photosphere, chromosphere, transition region and low corona layers of the solar atmosphere. Using the high temporal and high spatial resolution observations taken by the Solar Magnetic Activity Research Telescope at Hida Observatory and the Atmospheric Imaging Assembly (AIA) onboard Solar Dynamic Observatory, we find that the wave evolved synchronously at different heights of the solar atmosphere, and it propagated at a speed of 605 km/s and showed a significant deceleration (-424 m/s2) in the extreme-ultraviolet (EUV) observations. During the initial stage, the wave speed in the EUV observations was 1000 km/s, similar to those measured from the AIA 1700 Å (967 km/s) and 1600 Å (893 km/s) observations. The wave was reflected by a remote region with open fields, and a slower wave-like feature at a speed of 220 km/s was also identified following the primary fast wave. In addition, a type-II radio burst was observed to be associated with the wave. We conclude that this wave should be a fast magnetosonic shock wave, which was firstly driven by the associated coronal mass ejection and then propagated freely in the corona. As the shock wave propagated, its legs swept the solar surface and thereby resulted in the wave signatures observed in the lower layers of the solar atmosphere. The slower wave-like structure following the primary wave was probably caused by the reconfiguration of the low coronal magnetic fields, as predicted in the field-line stretching model.

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arXiv2011

Kinematics and Fine Structure of An Unwinding Polar Jet Observed by SDO/AIA

We present an observational study of the kinematics and fine structure of an unwinding polar jet, with high temporal and spatial observations taken by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) and the Solar Magnetic Activity Research Telescope (SMART). During the rising period, the shape of the jet resembled a cylinder with helical structures on the surface, while the mass of the jet was mainly distributed on the cylinder's shell. In the radial direction, the jet expanded successively at its western side. The radial expansion presented three distinct phases: the gradually expanding phase, the fast expanding phase, and the steady phase. Each phase lasted for about 12 minutes. The angular speed of the unwinding jet and the twist transferred into the outer corona during the eruption are estimated to be 11.1 \times 10{-3} rad/s (period = 564 s) and 1.17 to 2.55 turns (or 2.34 to 5.1π) respectively. On the other hand, by calculating the azimuthal component of the magnetic field in the jet and comparing the free energy stored in the non-potential magnetic field with the jet's total energy, we find that the non-potential magnetic field in the jet is enough to supply the energy for the ejection. These new observational results strongly support the scenario that the jets are driven by the magnetic twist, which is stored in the twisted closed field of a bipole, and released through magnetic reconnection between the bipole and its ambient open field.

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arXiv2011

A Time Series of Filament Eruptions Observed by Three Eyes from Space: From Failed to Successful Eruptions

We present stereoscopic observations of six sequent eruptions of a filament in the active region NOAA 11045 on 2010 Feb 8, with the advantage of the STEREO twin viewpoints in combination with the earth viewpoint from SOHO instruments and ground-based telescopes. The last one of the six eruptions is with a coronal mass ejection, while the others are not. The flare in this successful one is more intensive than in the others. Moreover, the filament material velocity of the successful one is also the largest among them. Interestingly, all the filament velocities are found proportional to their flare powers. We calculate magnetic field intensity at low altitude, the decay indexes of the external field above the filament, and the asymmetry properties of the overlying fields before and after the failed eruptions and find little difference between them, indicating the same coronal confinement for the failed and the successful eruptions. The results suggest that, besides the confinement of coronal magnetic field, the energy released in low corona should be another crucial element for production of a failed or successful filament eruption. That is, only a coronal mass ejection can be launched away if the energy released exceeds some critical value, given the same coronal conditions.

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