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Nonlinear Force-Free Field Extrapolation of a Coronal Magnetic Flux Rope Supporting a Large-Scale Filament from Photospheric Vector Magnetogram  

Chaowei Jiang   Submitted: 2014-04-03 09:11

Solar filament are commonly thought to be supported in magnetic dips, in particular, of magnetic flux ropes (FRs). In this Letter, from the observed photospheric vector magnetogram, we implement a nonlinear force-free field (NLFFF) extrapolation of a coronal magnetic FR that supports a large-scale intermediate filament between an active region and a weak polarity region. This result is the first in that current NLFFF extrapolations with presence of FRs are limited to relatively small-scale filaments that are close to sunspots and along main polarity inversion line (PIL) with strong transverse field and magnetic shear, and the existence of a FR is usually predictable. In contrast, the present filament lies along the weak-field region (photospheric field strength ≲100 G), where the PIL is very fragmented due to small parasitic polarities on both side of the PIL and the transverse field has a low value of signal-to-noise ratio. Thus it represents a far more difficult challenge to extrapolate a large-scale FR in such case. We demonstrate that our CESE-MHD-NLFFF code is competent for the challenge. The numerically reproduced magnetic dips of the extrapolated FR match observations of the filament and its barbs very well, which supports strongly the FR-dip model for filaments. The filament is stably sustained because the FR is weakly twisted and strongly confined by the overlying closed arcades.

Authors: Chaowei Jiang, S. T. Wu, Xueshang Feng, Qiang Hu
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted by ApJL
Last Modified: 2014-04-07 10:55
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Formation and Eruption of an Active Region Sigmoid: I. Study by Nonlinear Force-Free Field Modeling  

Chaowei Jiang   Submitted: 2013-10-30 20:55

We present a magnetic analysis of the formation and eruption of an active region (AR) sigmoid in AR 11283 from 2011 September 4 to 6. To follow the quasi-static evolution of the coronal magnetic field, we reconstruct a time sequence of static fields using a recently developed nonlinear force-free field model constrained by the SDO/HMI vector magnetograms. A detailed analysis of the fields compared with the SDO/AIA observations suggests the following scenario for the evolution of the region. Initially, a new bipole emerges into the negative polarity of a pre-existing bipolar AR, forming a null point topology between the two flux systems. A weakly twisted flux rope (FR) is then built up slowly in the embedded core region, largely through flux-cancellation photospheric reconnections, forming a bald patch separatrix surface (BPSS) separating the FR from its ambient field. The FR grows gradually until its axis runs into a torus instability (TI) domain near the end of the third day, and the BPSS also develops a fully S-shape. Unlike in the case of standard TI, the FR does not erupt instantly since it is still attached at the photosphere along the bald patch (BP) portion of the polarity inversion line. The combined effects of the TI-driven expansion of the FR and the line-tying at the BP tear the FR into two parts with the upper portion freely expelled and the lower portion remaining behind the post-flare arcades. This process dynamically perturbs the BPSS and results in the transient enhanced brightening of the sigmoid. The accelerated expansion of the upper portion of the FR strongly pushes its envelope flux near the null point and triggers breakout reconnection at the null, as evidenced by a remarkable circular flare ribbon, which further facilitates the eruption. We discuss the important implications of these results for the formation and disruption of sigmoid region with FR.

Authors: Chaowei Jiang, S. T. Wu, Xueshang Feng, Qiang Hu
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted by ApJ
Last Modified: 2013-10-31 08:18
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MHD Simulation of a Sigmoid Eruption of Active Region 11283  

Chaowei Jiang   Submitted: 2013-06-10 22:26

Current magnetohydrodynamic (MHD) simulations of the initiation of solar eruptions are still commonly carried out with idealized magnetic field models, whereas the realistic coronal field prior to eruptions can possibly be reconstructed from the observable photospheric field. Using a nonlinear force-free field extrapolation prior to a sigmoid eruption in AR 11283 as the initial condition in a MHD model, we successfully simulate the realistic initiation process of the eruption event, as is confirmed by a remarkable resemblance to the SDO/AIA observations. Analysis of the pre-eruption field reveals that the envelope flux of the sigmoidal core contains a coronal null and furthermore the flux rope is prone to a torus instability. Observations suggest that reconnection at the null cuts overlying tethers and likely triggers the torus instability of the flux rope, which results in the eruption. This kind of simulation demonstrates the capability of modeling the realistic solar eruptions to provide the initiation process.

Authors: Chaowei Jiang, Xueshang Feng, S. T. Wu, Qiang Hu
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted for ApJL
Last Modified: 2013-06-11 11:31
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Preprocess the Photospheric Vector Magnetograms for NLFFF Extrapolation using a Potential Field Model and an Optimization Method  

Chaowei Jiang   Submitted: 2013-06-09 22:04

Numerical reconstruction/extrapolation of coronal nonlinear force-free magnetic field (NLFFF) usually takes the photospheric vector magnetogram as input at the bottom boundary. Magnetic field observed at the photosphere, however, contains force which is in conflict with the fundamental assumption of the force-free model and measurement noise which is unfavorable for practical computation. Preprocessing of the raw magnetogram has been proposed by Wiegelmann, Inhester, and Sakurai (2006) to remove the force and noise for providing better input for NLFFF modeling. In this paper we develop a new code of magnetogram preprocessing which is consistent with our extrapolation method CESE-MHD-NLFFF (Jiang, Feng, and Xiang, 2012; Jiang and Feng, 2012). Basing on a magnetic-splitting rule that a magnetic field can be split into a potential field part and a non-potential part, we split the magnetogram and deal with the two parts separately. Preprocessing of the magnetogram's potential part is based on a numerical potential field model, and the non-potential part is preprocessed using the similar optimization method of Wiegelmann et al (2006). The code is applied to the SDO/HMI data and results show that the method can remove efficiently the force and noise and improve the quality of extrapolation.

Authors: Chaowei Jiang, Xueshang Feng
Projects: SDO-HMI

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2013-06-10 09:38
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Extrapolation of the Solar Coronal Magnetic Field from SDO/HMI Magnetogram by a CESE-MHD-NLFFF Code  

Chaowei Jiang   Submitted: 2013-06-06 23:56

Due to the absence of direct measurement, the magnetic field in the solar corona is usually extrapolated from the photosphere in numerical way. At the moment, the nonlinear force-free field (NLFFF) model dominates the physical models for field extrapolation in the low corona. Recently we have developed a new NLFFF model with MHD relaxation to reconstruct the coronal magnetic field. This method is based on CESE-MHD model with the conservation-element/solution-element (CESE) spacetime scheme. In this paper, we report the application of the CESE-MHD-NLFFF code to SDO/HMI data with magnetograms sampled for two active regions (ARs), NOAA AR 11158 and 11283, both of which were very non-potential, producing X-class flares and eruptions. The raw magnetograms are preprocessed to remove the force and then inputted into the extrapolation code. Qualitative comparison of the results with the SDO/AIA images shows that our code can reconstruct magnetic field lines resembling the EUV-observed coronal loops. Most important structures of the active regions are reproduced excellently, like the highly-sheared field lines that suspend filaments in AR 11158 and twisted flux rope which corresponds to a sigmoid in AR 11283. Quantitative assess of the results shows that the force-free constraint is fulfilled very well in the strong-field regions but apparently not that well in the weak-field regions because of data noise and numerical errors in the small currents.

Authors: Chaowei Jiang, Xueshang Feng
Projects: SDO-AIA,SDO-HMI

Publication Status: ApJ, 2013, 769, 144
Last Modified: 2013-06-07 21:16
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Abstracts by Author
Investigations of Sizes and Dynamical Motions of Solar Photospheric Granules by a Novel Granular Segmenting Algorithm
Formation of Magnetic Flux Rope during Solar Eruption. I. Evolution of Toroidal Flux and Reconnection Flux
A fundamental mechanism of solar eruption initiation
Structure and Evolution of an Inter–Active Region Large-scale Magnetic Flux Rope
Variation of Magnetic Flux Ropes through Major Solar Flares
MHD Modeling of Solar Coronal Magnetic Evolution Driven by Photospheric Flow
The Causes of Peripheral Coronal Loop Contraction and Disappearance Revealed in a Magnetohydrodynamic Simulation of Solar Eruption
Data-driven MHD Simulation of the Formation and Initiation of a Large-scale Pre-flare Magnetic Flux Rope in Solar Active Region 12371
Continuous Null-Point Magnetic Reconnection Builds Up a Torus Unstable Magnetic Flux Rope Triggering the X9.3 Flare in Solar Active Region~12673
A Study of Pre-Flare Solar Coronal Magnetic Fields: Magnetic Flux Ropes
A Statistical Study of Solar Filament Eruptions That Forms High-Speed Coronal Mass Ejections
A Two-Step Magnetic Reconnection in a Confined X-class Flare in Solar Active Region 12673
Formation and Eruption of an Active Region Sigmoid. II. Magnetohydrodynamic Simulation of a Multistage Eruption
Reconstruction of a Large-scale Pre-flare Coronal Current Sheet Associated with an Homologous X-shaped Flare
Comparison of Two Coronal Magnetic Field Models for Reconstructing a Sigmoidal Solar Active Region With Coronal Loops
A Magnetic Bald-Patch Flare in Solar Active Region 11117
How did a Major Confined Flare Occur in Super Solar Active Region 12192?
Data-driven magnetohydrodynamic modelling of a flux-emerging active region leading to solar eruption
A Comparison Study of a Solar Active-Region Eruptive Filament and a Neighboring Non-Eruptive Filament
Testing a Solar Coronal Magnetic Field Extrapolation Code with the Titov-Demoulin Magnetic Flux Rope Model
Nonlinear Force-Free Field Extrapolation of a Coronal Magnetic Flux Rope Supporting a Large-Scale Filament from Photospheric Vector Magnetogram
Formation and Eruption of an Active Region Sigmoid: I. Study by Nonlinear Force-Free Field Modeling
MHD Simulation of a Sigmoid Eruption of Active Region 11283
Preprocess the Photospheric Vector Magnetograms for NLFFF Extrapolation using a Potential Field Model and an Optimization Method
Extrapolation of the Solar Coronal Magnetic Field from SDO/HMI Magnetogram by a CESE--MHD--NLFFF Code

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