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Onset of a Large Ejective Solar Eruption from a Typical Coronal-Jet-Base Field Configuration  

Navin Chandra Joshi   Submitted: 2017-07-04 22:04

Utilizing multiwavelength observations and magnetic field data from SDO/AIA, SDO/HMI, GOES and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive three-ribbon flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two ribbons. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity-inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread part from that polarity-inversion line; this evolution is consistent with the tether-cutting-reconnection mechanism for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core under goes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (12 min) circular ribbon onset, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale (circular-ribbon diameter 100000 km) eruption is analogous to that of coronal jets (base size 10000 km), many of which, according to recent findings, result from eruptions of small-scale minifilaments. Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan-spine null-point magnetic topology happen on a wide range of size scales on the Sun.

Authors: Navin Chandra Joshi, Alphonse C. Sterling, Ronald L. Moore, Tetsuya Magara, Young-Jae Moon
Projects: GOES X-rays,RHESSI,SDO-AIA,SDO-HMI,SoHO-LASCO

Publication Status: Accepted for publication in ApJ Journal.
Last Modified: 2017-07-05 12:50
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Interaction of Two Filament Channels of Different Chiralities  

Navin Chandra Joshi   Submitted: 2016-05-11 03:51

We present observations of interactions between the two filament channels of different chiralities and associated dynamics that occurred during 2014 April 18-20. While two flux ropes of different helicity with parallel axial magnetic fields can only undergo a bounce interaction when they are brought together, the observations at the first glance show that the heated plasma is moving from one filament channel to the other. The SDO/AIA 171 Å observations and the PFSS magnetic field extrapolation reveal the presence of fan-spine magnetic configuration over the filament channels with a null point located above them. Three different events of filament activations, partial eruptions, and associated filament channel interactions have been observed. The activation initiated in one filament channel seems to propagate along the neighbour filament channel. We believe that the activation and partial eruption of the filaments bring the field lines of flux ropes containing them closer to the null point and trigger the magnetic reconnection between them and the fan-spine magnetic configuration. As a result, the hot plasma moves along the outer spine line toward the remote point. Utilizing the present observations, for the first time we have discussed how two different-chirality filament channels can interact and show interrelation.

Authors: Navin Chandra Joshi, Boris Filippov, Brigitte Schmieder, Tetsuya Magara, Young-Jae, Moon, Wahab Uddin
Projects: GONG,SDO-AIA,SDO-HMI

Publication Status: Accepted for publication in ApJ.
Last Modified: 2016-05-11 08:53
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The Role of Erupting Sigmoid in Triggering a Flare with Parallel and Large-Scale Quasi-Circular Ribbons  

Navin Chandra Joshi   Submitted: 2015-09-07 21:28

In this paper, we present observations and analysis of an interesting sigmoid formation, eruption and the associated flare that occurred on 2014 April 18 using multi-wavelength data sets. We discuss the possible role of the sigmoid eruption in triggering the flare, which consists of two different set of ribbons: parallel ribbons as well as a large-scale quasi-circular ribbon. Several observational evidence and nonlinear force-free field extrapolation results show the existence of a large-scale fan-spine type magnetic configuration with a sigmoid lying under a section of the fan dome. The event can be explained with the following two phases. During the pre-flare phase, we observed the formation and appearance of sigmoid via tether-cutting reconnection between the two sets of sheared fields under the fan dome. The second, main flare phase, features the eruption of the sigmoid, the subsequent flare with parallel ribbons, and a quasi-circular ribbon. We propose the following multi-stage successive reconnections scenario for the main flare. First, tether-cutting reconnection is responsible for the formation and the eruption of the sigmoid structure. Second, the reconnection occurred in the wake of the erupting sigmoid produces the parallel flare ribbons on the both sides of the circular polarity inversion line. Third, the null-type reconnection higher in the corona, possibly triggered by the erupting sigmoid, leads to the formation of a large quasi-circular ribbon. For the first time we suggest a mechanism for this type of flare consisting of a double set of ribbons triggered by an erupting sigmoid in a large scale fan-spine type magnetic configuration.

Authors: Navin Chandra Joshi, Chang Liu, Xudong Sun, Haimin Wang, Tetsuya Magara, Y.-J. Moon
Projects: RHESSI,SDO-AIA,SDO-HMI

Publication Status: Accepted for Publication in ApJ
Last Modified: 2015-09-08 05:18
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Formation of Compound Flux Rope by The Merging of Two Filament Channels, Associated Dynamics and its Stability  

Navin Chandra Joshi   Submitted: 2014-09-05 04:57

We present the observations of compound flux rope formation via merging of two nearby filament channels, associated dynamics and its stability that occurred on 2014 January 1 using multiwavelength data. We have also discussed the dynamics of cool and hot plasma moving along the newly formed compound flux rope. The merging started after the interaction between the southern leg of northward filament and the northern leg of the southward filament at ≈01:21 UT and continue until a compound flux rope formed at ≈01:33 UT. During the merging the cool filaments plasma heated up and started to move along the both side of the compound flux rope i.e., toward north (≈265 km s-1 ) and south (≈118 km s-1 ) from the point of merging. After traveling a distance of ≈150 Mm towards north the plasma become cool and started to returns back towards south (≈14 km s-1 ) after ≈02:00 UT. The observations provide an clear example of compound flux rope formation via merging of two different flux ropes and occurrence of flare through tether cutting reconnection. However, the compound flux rope remained stable in the corona and made an confined eruption. The coronal magnetic field decay index measurements revealed that both the filaments and the compound flux rope axis lies within the stability domain (decay index < 1.5), which may be the possible cause for their stability. The present study also deals with the relationship between the filaments chirality (sinistral) and the helicity (positive) of the surrounding flux rope.

Authors: Navin Chandra Joshi, Tetsuya Magara and Satoshi Inoue
Projects: GONG,SDO-AIA,SDO-HMI

Publication Status: Accepted for Publication in ApJ
Last Modified: 2014-09-05 10:14
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Abstracts by Author
Onset of a Large Ejective Solar Eruption from a Typical Coronal-Jet-Base Field Configuration
Interaction of Two Filament Channels of Different Chiralities
The Role of Erupting Sigmoid in Triggering a Flare with Parallel and Large-Scale Quasi-Circular Ribbons
Formation of Compound Flux Rope by The Merging of Two Filament Channels, Associated Dynamics and its Stability

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