Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEruptive-Impulsive Homologous M-class Flares Associated with Double-Decker Flux Rope Configuration in Mini-Sigmoid of NOAA 12673
199
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a multiwavelength analysis of two homologous, short lived, impulsive flares of GOES class M1.4 and M7.3, that occurred from a very localized mini-sigmoid region within the active region NOAA 12673 on 2017 September 7. Both flares were associated with initial jet-like plasma ejection which for a brief amount of time moved toward east in a collimated manner before drastically changing direction toward southwest. Non-linear force-free field extrapolation reveals the presence of a compact double-decker flux rope configuration in the mini-sigmoid region prior to the flares. A set of open field lines originating near the active region which were most likely responsible for the anomalous dynamics of the erupted plasma, gave the earliest indication of an emerging coronal hole near the active region. The horizontal field distribution suggests a rapid decay of the field above the active region, implying high proneness of the flux rope system toward eruption. In view of the low coronal double-decker flux ropes and compact extreme ultra-violet (EUV) brightening beneath the filament along with associated photospheric magnetic field changes, our analysis supports the combination of initial tether-cutting reconnection and subsequent torus instability for driving the eruption.
rate research
Read More
Magnetic flux ropes (MFRs) are believed to be the core structure in solar eruptions, nevertheless, their formation remains intensely debated. Here we report a rapid buildup process of an MFR-system during a confined X2.2 class flare occurred on 2017 September 6 in NOAA AR 12673, three hours after which the structure erupted to a major coronal mass ejection (CME) accompanied by an X9.3 class flare. For the X2.2 flare, we do not find EUV dimmings, separation of its flare ribbons, or clear CME signatures, suggesting a confined flare. For the X9.3 flare, large-scale dimmings, separation of its flare ribbons, and a CME show it to be eruptive. By performing a time sequence of nonlinear force-free fields (NLFFFs) extrapolations we find that: until the eruptive flare, an MFR-system was located in the AR. During the confined flare, the axial flux and the lower bound of the magnetic helicity for the MFR-system were dramatically enhanced by about 86% and 260%, respectively, although the mean twist number was almost unchanged. During the eruptive flare, the three parameters were all significantly reduced. The results evidence the buildup and release of the MFR-system during the confined and the eruptive flare, respectively. The former may be achieved by flare reconnection. We also calculate the pre-flare distributions of the decay index above the main polarity inversion line (PIL) and find no significant difference. It indicates that the buildup of the magnetic flux and helicity of the MFR-system may play a role in facilitating its final eruption.
In this article, we investigate the formation and disruption of a coronal sigmoid from the active region (AR) NOAA 11909 on 07 December 2013, by analyzing multi-wavelength and multi-instrument observations. Our analysis suggests that the formation of `transient sigmoid initiated $approx$1 hour before its eruption through a coupling between two twisted coronal loop systems. A comparison between coronal and photospheric images suggests that the coronal sigmoid was formed over a simple $beta$-type AR which also possessed dispersed magnetic field structure in the photosphere. The line-of-sight photospheric magnetograms also reveal moving magnetic features, small-scale flux cancellation events near the PIL, and overall flux cancellation during the extended pre-eruption phase which suggest the role of tether-cutting reconnection toward the build-up of the flux rope. The disruption of the sigmoid proceeded with a two-ribbon eruptive M1.2 flare (SOL2013-12-07T07:29). In radio frequencies, we observe type III and type II bursts in meter wavelengths during the impulsive phase of the flare. The successful eruption of the flux rope leads to a fast coronal mass ejection (with a linear speed of $approx$1085 km s -1 ) in SOHO/LASCO field-of-view. During the evolution of the flare, we clearly observe typical sigmoid-to-arcade transformation. Prior to the onset of the impulsive phase of the flare, flux rope undergoes a slow rise ($approx$15 km s -1 ) which subsequently transitions into a fast eruption ($approx$110 km s -1 ). The two-phase evolution of the flux rope shows temporal associations with the soft X-ray precursor and impulsive phase emissions of the M-class flare, respectively, thus pointing toward a feedback relationship between magnetic reconnection and early CME dynamics.
In this work, we investigate the formation of a magnetic flux rope (MFR) above the central polarity inversion line (PIL) of NOAA Active Region 12673 during its early emergence phase. Through analyzing the photospheric vector magnetic field, extreme ultraviolet (EUV) and ultraviolet (UV) images, extrapolated three-dimensional (3D) non-linear force-free fields (NLFFFs), as well as the photospheric motions, we find that with the successive emergence of different bipoles in the central region, the conjugate polarities separate, resulting in collision between the non-conjugated opposite polarities. Nearly-potential loops appear above the PIL at first, then get sheared and merge at the collision locations as evidenced by the appearance of a continuous EUV sigmoid on 2017 September 4, which also indicates the formation of an MFR. The 3D NLFFFs further reveal the gradual buildup of the MFR, accompanied by the appearance of two elongated bald patches (BPs) at the collision locations and a very low-lying hyperbolic flux tube configuration between the BPs. The final MFR has relatively steady axial flux and average twist number of around $2.1times 10^{20}$~Mx and -1.5, respective. Shearing motions are found developing near the BPs when the collision occurs, with flux cancellation and UV brightenings being observed simultaneously, indicating the development of a process named as collisional shearing (firstly identified by Chintzoglou et al. 2019). The results clearly show that the MFR is formed by collisional shearing, i.e., through shearing and flux cancellation driven by the collision between non-conjugated opposite polarities during their emergence.
We investigate the formation, activation and eruption of a flux rope from the sigmoid active region NOAA 11719 by analyzing E(UV), X-ray and radio measurements. During the pre-eruption period of ~7 hours, the AIA 94 A images reveal the emergence of a coronal sigmoid through the interaction between two J-shaped bundles of loops which proceeds with multiple episodes of coronal loop brightenings and significant variations in the magnetic flux through the photosphere. These observations imply that repetitive magnetic reconnections likely play a key role in the formation of the sigmoidal flux rope in the corona and also contribute toward sustaining the temperature of the flux rope higher than the ambient coronal structures. Notably, the formation of the sigmoid is associated with the fast morphological evolution of an S-shaped filament channel in the chromosphere. The sigmoid activates toward eruption with the ascend of a large flux rope in the corona which is preceded by the decrease of photospheric magnetic flux through the core flaring region suggesting tether-cutting reconnection as a possible triggering mechanism. The flux rope eruption results in a two-ribbon M6.5 flare with a prolonged rise phase of ~21 min. The flare exhibits significant deviation from the standard flare model in the early rise phase during which a pair of J-shaped flare ribbons form and apparently exhibit converging motions parallel to the polarity inversion line which is further confirmed by the motions of HXR footpoint sources. In the later stages, the flare follows the standard flare model and the source region undergoes a complete sigmoid-to-arcade transformation.
In this paper, we address the formation of a magnetic flux rope (MFR) that erupted on 2012 July 12 and caused a strong geomagnetic storm event on July 15. Through analyzing the long-term evolution of the associated active region observed by the Atmospheric Imaging Assembly and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, it is found that the twisted field of an MFR, indicated by a continuous S-shaped sigmoid, is built up from two groups of sheared arcades near the main polarity inversion line half day before the eruption. The temperature within the twisted field and sheared arcades is higher than that of the ambient volume, suggesting that magnetic reconnection most likely works there. The driver behind the reconnection is attributed to shearing and converging motions at magnetic footpoints with velocities in the range of 0.1--0.6 km s$^{-1}$. The rotation of the preceding sunspot also contributes to the MFR buildup. Extrapolated three-dimensional non-linear force-free field structures further reveal the locations of the reconnection to be in a bald-patch region and in a hyperbolic flux tube. About two hours before the eruption, indications for a second MFR in the form of an S-shaped hot channel are seen. It lies above the original MFR that continuously exists and includes a filament. The whole structure thus makes up a stable double-decker MFR system for hours prior to the eruption. Eventually, after entering the domain of instability, the high-lying MFR impulsively erupts to generate a fast coronal mass ejection and X-class flare; while the low-lying MFR remains behind and continuously maintains the sigmoidicity of the active region.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
