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Untwisting and Disintegration of a Solar Filament Associated with Photospheric Flux Cancellation  

Huadong Chen   Submitted: 2018-12-19 02:27

Using the high-resolution observations from New Vacuum Solar Telescope (NVST) jointly with the Solar Dynamics Observatory data, we investigate two successive confined eruptions (Erup1 and Erup2) of a small filament in a decaying active region on 2017 November 10. During the process of Erup1, the overlying magnetic arcade is observed to inflate with the rising filament at beginning and then stop the ongoing of the explosion. In the hot EUV channel, a coronal sigmoidal structure appears during the first eruption and fade away after the second one. The untwisting rotation and disintegration of the filament in Erup2 are clearly revealed by the NVST Hα intensity data, hinting at a pre-existing twisted configuration of the filament. By tracking two rotating features in the filament, the average rotational angular velocity of the unwinding filament is found to be ~10.5 degree/min. A total twist of ~1.3 π is estimated to be stored in the filament before the eruption, which is far below the criteria for kink instability. In the course of several hours prior to the event, some photospheric flux activities, including the flux convergence and cancellation, are detected around the northern end of the filament, where some small-scale EUV brightenings are also captured. Moreover, strongly-sheared transverse fields are found in the cancelling magnetic features from the vector magnetograms. Our observational results support the flux cancellation model, in which the interaction between the converging and sheared opposite-polarity fluxes destabilizes the filament and triggers the ensuing ejection.

Authors: Huadong Chen, Ruisheng Zheng, Leping Li, Suli Ma, Yi Bi, and Shuhong Yang
Projects: New Vacuum Solar Telescope (NVST),SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in the ApJ
Last Modified: 2018-12-19 12:30
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Confined Flares in Solar Active Region 12192 from 2014 October 18 to 29  

Huadong Chen   Submitted: 2015-07-03 19:44

Using the observations from the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO), we investigate six X-class and twenty- nine M-class flares occurring in solar active region (AR) 12192 from October 18 to 29. Among them, thirty (including six X- and twenty-four M-class) flares originated from the AR core and the other five M-flares appeared at the AR periphery. Four of the X-flares exhibited similar flaring structures, indicating they were homologous flares with analogous triggering mechanism. The possible scenario is: photospheric motions of emerged magnetic fluxes lead to shearing of the associated coronal magnetic field, which then yields a tether-cutting favorable configuration. Among the five periphery M-flares, four were associated with jet activities. The HMI vertical magnetic field data show that the photospheric fluxes of opposite magnetic polarities emerged, converged and canceled with each other at the footpoints of the jets before the flares. Only one M-flare from the AR periphery was followed by a coronal mass ejection (CME). From October 20 to 26, the mean decay index of the horizontal background field within the height range of 40x105 Mm is below the typical threshold for torus instability onset. This suggests that a strong confinement from the overlying magnetic field might be responsible for the poor CME production of AR 12192.

Authors: Huadong Chen, Jun Zhang, Suli Ma, Shuhong Yang, Leping Li, Xin Huang, Junmin Xiao
Projects: None

Publication Status: ApJL (Accepted)
Last Modified: 2015-07-04 02:30
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Huadong Chen   Submitted: 2014-12-04 20:46

Using multi-wavelength data from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we investigated two successive solar flares, a C5.1 confined flare and an X4.9 ejective flare with a halo coronal mass ejection, in NOAA active region 11990 from 2014 February 24 to 25. Before the confined flare onset, EUV brightening beneath the filament was detected. As the flare began, a twisted helical flux rope (FR) wrapping around the filament moved upward and then stopped, and in the meantime an obvious X-ray source below it was observed. Prior to the ejective X4.9 flare, some pre-existing loop structures in the active region interacted with each other, which produced a brightening region beneath the filament. Meanwhile, a small flaring loop appeared below the interaction region and some new helical lines connecting the far ends of the loop structures were gradually formed and continually added into the former twisted FR. Then, due to the resulting imbalance between the magnetic pressure and tension, the new FR, together with the filament, erupted outward. Our observations coincide well with a tether-cutting model, suggesting that the two flares probably have the same triggering mechanism, i.e., tether-cutting reconnection. To our knowledge, this is the first direct observation of tether-cutting reconnection occurring between pre-existing loops in an active region. In the ejective flare case, the erupting filament exhibited an Ω-like kinked structure and underwent an exponential rise after a slow-rise phase, indicating that the kink instability might be also responsible for the eruption initiation.

Authors: Huadong Chen, Jun Zhang, Xin Cheng, Suli Ma, Shuhong Yang, and Ting Li
Projects: None

Publication Status: Published by APJL
Last Modified: 2014-12-05 13:40
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Subject will be restored when possible  

Huadong Chen   Submitted: 2008-02-22 00:53

Aims. To know more about the physical origin of surges and jets, we investigated seven successive surge events, which occurred above the satellite sunspots of active region NOAA 10720 on 2005 January 15. Methods. Using data from the Transition Region and Coronal Explorer (TRACE), Big Bear Solar Observatory (BBSO) and Solar and Heliospheric Observatory (SOHO), we present a detailed study of the surges and their relations with the associated small arch filament, UV jets, flares and photospheric longitudinal magnetic fields. Results. The seven Hα surges we studied repeatedly occurred where the photospheric longitudinal fluxes of opposite magnetic polarities emerged, converged and were canceled by each other. Correspondingly, a small satellite spot emerged, decayed and disappeared during a period of about 2 hours in the white-light observations. In morphology, all surges displayed almost linear ejective structures. Their dynamic properties, such as the transverse velocity, projected maximum length and lifetime, varied in wide ranges. They are 30?200 km s-1, 38 000?220 000 km and from several to tens of minutes, respectively. Correspondingly, the intensities of their correlated microflares were different too. The surges of major velocities or maximum lengths seemed to be accompanied by processes of more energy release. Prior to these surge events, a small Hα arch filament connecting the opposite flux elements was found at the base region. Instead of erupting completely, it gradually disappeared during the surges. Its role in the surge activities is very like a bipolar flux, which contained the cool plasma and reconnected with the ambient magnetic fields. In 1600 Å, three surge events exhibited the composite structures of bright jets and nearby small flaring loops, which provides direct evidence of magnetic reconnection origin of the surges. A careful comparison revealed that the ends of the arch filament, the UV jets and the small flaring loops just corresponded to the interacting longitudinal fluxes in the photosphere. Conclusions. These observational results support the magnetic reconnection model of surges and jets.

Authors: H. D. Chen, Y. C. Jiang, & S. L. Ma
Projects: None

Publication Status: Published, A&A, 2008, 478, 907-913
Last Modified: 2008-09-23 21:22
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Untwisting and Disintegration of a Solar Filament Associated with Photospheric Flux Cancellation
Confined Flares in Solar Active Region 12192 from 2014 October 18 to 29
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