arXiv subjects

S. H. Yang

Publications and source records attributed to S. H. Yang.

8 recordsLinked to original sources

arXiv2024

Unraveling the untwisting process and upward mass transfer of a twisted prominence driven by vortex motion

Solar filaments/prominences are common features in the Sun's atmosphere that contain cool chromospheric material suspended within the hot corona. However, the intricate topology of these structures and the mechanisms driving their instability and upward material transfer are not well understood. This study is to analyze a specific twisted prominence on February 10, 2021, and to explore its dynamics, including stability, motion, and material transfer. The study utilizes high-resolution H$α$ observations from the 1-m New Vacuum Solar Telescope and space-borne observations from the Solar Dynamics Observatory. We analyzed the data to investigate the characteristics and behavior of the twisted prominence. We also detected and measured the outflow speed surrounding the prominence. The study reveals that the observed prominence exhibited a stretched and twisted structure at its apex, distinguishing it from familiar cloudy prominences. Following more than 30 hours of equilibrium, the prominence destabilized, leading to a series of dynamic phenomena, such as vortex motion, oscillations, resonations, untwisting, and the upward transfer of mass. Consequently, material from the top of the prominence was carried upward and deposited into the overlying magnetic arcades. Noteworthy, outflows surrounding the prominence were characterized by speeds exceeding 40 km $s^{-1}$. We propose, for the first time, a mechanism rooted in the Kármán Vortex Street instability to explain the destabilization of the prominence. The estimated typical Strouhal Number of 0.23$\pm$0.06, which is related to vortex shedding, falls within the expected range for the Kármán Vortex Street effect, as predicted by simulations. These discoveries provide new insights into the dynamics and fundamental topology of solar prominences and reveal a previously unknown mechanism for mass loading into the upper atmosphere.

astro-ph.SR↗

arXiv2021

The Blow-off Impulse Equivalence between Multi-Energy Composite Spectrum Electron Beam and Powerful Pulsed X-ray

The electron beam, one of the most effective approaches to simulate the irradiation effects of powerful pulsed X-ray in the laboratory, plays an important role in the experiment of simulating thermodynamic effects of powerful pulsed X-ray. This paper studies the thermodynamics equivalence between multi-energy composite spectrum electron beam and blackbody spectrum X-ray, which is helpful to quickly determine the experimental parameters in the simulation experiment. The experimental data of electron beam is extrapolated by the numerical calculation, to increase the range of energy flux. Through calculating the blow-off impulse of blackbody spectrum X-ray irradiation, we obtained the curve of X-ray blow-off impulse varying with energy flux, and then found two categories of equivalent relations - equal-energy flux and equal-impulse - by analysing the calculation results of electron beam and X-ray blow-off impulse. Based on such relations, we could directly or indirectly obtain the results of blackbody spectrum X-ray irradiation blow-off impulse via electron beam experiment.

physics.app-ph↗

arXiv2020

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Penumbral filaments and light bridges are prominent structures inside sunspots and are important for understanding the nature of sunspot magnetic fields and magneto-convection underneath. We investigate an interesting event where several penumbral filaments intruded into a sunspot light bridge for more insights into magnetic fields of the sunspot penumbral filament and light bridge, as well as their interaction. The emission, kinematic, and magnetic topology characteristics of the penumbral filaments intruding into the light bridge and the resultant jets are studied. At the west part of the light bridge, the intruding penumbral filaments penetrated into the umbrae on both sides of the light bridge, and two groups of jets were also detected. The jets shared the same projected morphology with the intruding filaments and were accompanied by intermittent footpoint brightenings. Simultaneous spectral imaging observations provide convincing evidences for the presences of magnetic reconnection related heating and bidirectional flows near the jet bases and contribute to measuring vector velocities of the jets. Additionally, nonlinear force-free field extrapolation results reveal strong and highly inclined magnetic fields along the intruding penumbral filaments, consistent well with the results deduced from the vector velocities of the jets. Therefore, we propose that the jets could be caused by magnetic reconnections between emerging fields within the light bridge and the nearly horizontal fields of intruding filaments. They were then ejected outward along the stronger filaments fields. Our study indicates that magnetic reconnection could occur between the penumbral filament fields and emerging fields within light bridge and produce jets along the stronger filament fields. These results further complement the study of magnetic reconnection and dynamic activities within the sunspot.

astro-ph.SR↗

arXiv2020

Fast degradation of the circular flare ribbon on 2014 August 24

The separation and elongation motions of solar flare ribbons have extensively been investigated. The degradation and disappearance of ribbons have rarely been explored. In this paper, we report our multiwavelength observations of a C5.5 circular-ribbon flare associated with two jets (jet1 and jet2) on 2014 August 24, focusing on the fast degradation of the outer circular ribbon (CR). The flare, consisting of a short inner ribbon (IR) and outer CR, was triggered by the eruption of a minifilament. The brightness of IR and outer CR reached their maxima simultaneously at $\sim$04:58 UT in all AIA wavelengths. Subsequently, the short eastern part of CR faded out quickly in 1600 Å but gradually in EUV wavelengths. The long western part of CR degraded in the counterclockwise direction and experienced a deceleration. The degradation was distinctly divided into two phases: phase I with faster apparent speeds (58$-$69 km s$^{-1}$) and phase II with slower apparent speeds (29$-$35 km s$^{-1}$). The second phase stopped at $\sim$05:10 UT when the western CR totally disappeared. Besides the outward propagation of jet1, the jet spire experienced untwisting motion in the counterclockwise direction during 04:55$-$05:00 UT. We conclude that the event can be explained by the breakout jet model. The coherent brightenings of the IR and CR at $\sim$04:58 UT may result from the impulsive interchange reconnection near the null point, whereas sub-Alfvénic slipping motion of the western CR in the counterclockwise direction indicates the occurrence of slipping magnetic reconnection. Another possible explanation of the quick disappearance of the hot loops connecting to the western CR is that they are simply reconnected sequentially without the need for significant slippage after the null point reconnection.

astro-ph.SR↗

arXiv2018

A blowout jet associated with one obvious extreme-ultraviolet wave and one complicated coronal mass ejection event

In this paper, we present a detailed analysis of a coronal blowout jet eruption which was associated with an obvious extreme-ultraviolet (EUV) wave and one complicated coronal mass ejection (CME) event based on the multi-wavelength and multi-view-angle observations from {\sl Solar Dynamics Observatory} and {\sl Solar Terrestrial Relations Observatory}. It is found that the triggering of the blowout jet was due to the emergence and cancellation of magnetic fluxes on the photosphere. During the rising stage of the jet, the EUV wave appeared just ahead of the jet top, lasting about 4 minutes and at a speed of 458 - \speed{762}. In addition, obvious dark material is observed along the EUV jet body, which confirms the observation of a mini-filament eruption at the jet base in the chromosphere. Interestingly, two distinct but overlapped CME structures can be observed in corona together with the eruption of the blowout jet. One is in narrow jet-shape, while the other one is in bubble-shape. The jet-shaped component was unambiguously related with the outwardly running jet itself, while the bubble-like one might either be produced due to the reconstruction of the high coronal fields or by the internal reconnection during the mini-filament ejection according to the double-CME blowout jet model firstly proposed by Shen et al. (2012b), suggesting more observational evidence should be supplied to clear the current ambiguity based on large samples of blowout jets in future studies.

astro-ph.SR↗

arXiv2018

Eruption of a multi-flux-rope system in solar active region 12673 leading to the two largest flares in Solar Cycle 24

Solar active region (AR) 12673 in 2017 September produced two largest flares in Solar Cycle 24: the X9.3 flare on September 06 and the X8.2 flare on September 10. We attempt to investigate the evolutions of the two great flares and their associated complex magnetic system in detail. Aided by the NLFFF modeling, we identify a double-decker flux rope configuration above the polarity inversion line (PIL) in the AR core region. The north ends of these two flux ropes were rooted in a negative- polarity magnetic patch, which began to move along the PIL and rotate anticlockwise before the X9.3 flare on September 06. The strong shearing motion and rotation contributed to the destabilization of the two magnetic flux ropes, of which the upper one subsequently erupted upward due to the kink-instability. Then another two sets of twisted loop bundles beside these ropes were disturbed and successively erupted within 5 minutes like a chain reaction. Similarly, multiple ejecta components were detected to consecutively erupt during the X8.2 flare occurring in the same AR on September 10. We examine the evolution of the AR magnetic fields from September 03 to 06 and find that five dipoles emerged successively at the east of the main sunspot. The interactions between these dipoles took place continuously, accompanied by magnetic flux cancellations and strong shearing motions. In AR 12673, significant flux emergence and successive interactions between the different emerging dipoles resulted in a complex magnetic system, accompanied by the formations of multiple flux ropes and twisted loop bundles. We propose that the eruptions of a multi-flux-rope system resulted in the two largest flares in Solar Cycle 24.

astro-ph.SR↗

arXiv2016

Light Walls Around Sunspots Observed by the Interface Region Imaging Spectrograph

The Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of the chromosphere and transition region. We try to determine whether the light walls exist somewhere else in active regions besides light bridges. Employing half-year high tempo-spatial data from the IRIS, we find lots of light walls either around sunspots or above light bridges. For the first time, we report one light wall near an umbral-penumbral boundary and another along a neutral line between two small sunspots. These new observations reveal that these light walls are multi-layer and multi-thermal structures which occur along magnetic neutral lines in active regions.

astro-ph.SR↗

arXiv2009

Response of the solar atmosphere to magnetic field evolution in a coronal hole region

Methods. We study an equatorial CH observed simultaneously by HINODE and STEREO on July 27, 2007. The HINODE/SP maps are adopted to derive the physical parameters of the photosphere and to research the magnetic field evolution and distribution. The G band and Ca II H images with high tempo-spatial resolution from HINODE/BFI and the multi-wavelength data from STEREO/EUVI are utilized to study the corresponding atmospheric response of different overlying layers. Results. We explore an emerging dipole locating at the CH boundary. Mini-scale arch filaments (AFs) accompanying the emerging dipole were observed with the Ca II H line. During the separation of the dipolar footpoints, three AFs appeared and expanded in turn. The first AF divided into two segments in its late stage, while the second and third AFs erupted in their late stages. The lifetimes of these three AFs are 4, 6, 10 minutes, and the two intervals between the three divisions or eruptions are 18 and 12 minutes, respectively. We display an example of mixed-polarity flux emergence of IN fields within the CH and present the corresponding chromospheric response. With the increase of the integrated magnetic flux, the brightness of the Ca II H images exhibits an increasing trend. We also study magnetic flux cancellations of NT fields locating at the CH boundary and present the obvious chromospheric and coronal response. We notice that the brighter regions seen in the 171 A images are relevant to the interacting magnetic elements. By examining the magnetic NT and IN elements and the response of different atmospheric layers, we obtain good positive linear correlations between the NT magnetic flux densities and the brightness of both G band (correlation coefficient 0.85) and Ca II H (correlation coefficient 0.58).

astro-ph.SR↗