Spatial Relationship between Twist in Active Region Magnetic Fields and Solar Flares

Hahn, Michael; Gaard, S.; Jibben, Patricia R.; Canfield, R. C.; Nandy, Dibyendu

doi:10.1086/431893

Cited by 31 publications

(29 citation statements)

References 26 publications

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“…Even though the dips are plotted to 1 PSH this does not mean that material sitting in these dips will in fact be visible in Hα. An additional requirement for it to be visible is that the column mass along the line of sight be sufficiently high (≈1 × 10 −5 g cm −2 , Gouttebroze, Heinzel, and Vial, 1993;Heinzel and Anzer, 2006). Therefore after computing the dips a simple hydrostatic atmosphere model is applied to determine the column mass from different viewing angles.…”

Section: The Modelsmentioning

confidence: 99%

A Non-Linear Force-Free Field Model for the Evolving Magnetic Structure of Solar Filaments

Mackay

Ballegooijen

2009

Sol Phys

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In this paper the effect of a small magnetic element approaching the main body of a solar filament is considered through non-linear force-free field modeling. The filament is represented by a series of magnetic dips. Once the dips are calculated, a simple hydrostatic atmosphere model is applied to determine which structures have sufficient column mass depth to be visible in Hα. Two orientations of the bipole are considered, either parallel or anti-parallel to the overlying arcade. The magnetic polarity that lies closest to the filament is then advected towards the filament. Initially for both the dominant and minority polarity advected elements, right/left bearing barbs are produced for dextral/sinsitral filaments. The production of barbs due to dominant polarity elements is a new feature. In later stages the filament breaks into two dipped sections and takes a highly irregular, non-symmetrical form with multiple pillars. The two sections are connected by field lines with double dips even though the twist of the field is less than one turn. Reconnection is not found to play a key role in the break up of the filament. The non-linear force-free fields produce very different results to extrapolated linear-force free fields. For the cases considered here the linear forcefree field does not produce the break up of the filament nor the production of barbs as a result of dominant polarity elements.

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Section: The Modelsmentioning

confidence: 99%

A Non-Linear Force-Free Field Model for the Evolving Magnetic Structure of Solar Filaments

Mackay

Ballegooijen

2009

Sol Phys

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“…From a sample of 17 vector magnetograms, Falconer et al (2003) found that the length of the strong-field and strong-gradient main neutral line (Lsg) is a viable proxy for the overall non-potentiality of active regions that can be measured from longitudinal magnetograms. Hahn et al (2005) studied co-registered photospheric vector magnetograms and chromospheric Hα images for 29 flares and found that flares tend to originate in regions of a high twist gradient and lie close to chirality inversion lines.…”

Section: Introductionmentioning

confidence: 99%

Magnetic properties of flare-CME productive active regions and CME speed

Guo¹,

Zhang²,

Chumak

2006

A&A

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Aims. We study the properties of magnetic field of flare-coronal-mass-ejection (flare-CME) productive active regions and their statistic correlations with CME speed. Methods. We used a sample of 86 flare-CMEs in 55 solar active regions. Four measures, including the tilt angle (Tilt), total flux (Ft), length of the strong-field and strong-gradient main neutral line (Lsg) and effective distance (d E ), are used to quantify the properties of the magnetic field of flare-CME productive active regions. (4) The occurrence of 11 slow CMEs and 1 fast CME in β type regions with Lsg far below the threshold reminds us of some exceptions to be considered when Lsg with the threshold is used to predict the CME productivity of active regions.

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“…The parameter is also used as a measure of twist in observational studies (see Liu et al 2014or Hahn et al 2005. It should be noted that this is not the α we vary in Group 2 and we have denoted this as α L to differentiate between the two.…”

Section: Twistmentioning

confidence: 99%

Sunspot rotation

Sturrock

Hood

2016

A&A

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Context. Observations of flux emergence indicate that rotational velocities may develop within sunspots. However, the dependence of this rotation on sub-photospheric field strength and twist remains largely unknown. Aims. We investigate the effects of varying the initial field strength and twist of an emerging sub-photospheric magnetic flux tube on the rotation of the sunspots at the photosphere. Methods. We consider a simple model of a stratified domain with a sub-photospheric interior layer and three overlying atmospheric layers. A twisted arched flux tube is inserted in the interior and is allowed to rise into the atmosphere. To achieve this, the magnetohydrodynamic equations are solved using the Lagrangian-remap code, Lare3d. We perform a parameter study by independently varying the sub-photospheric magnetic field strength and twist. Results. Altering the initial magnetic field strength and twist of the flux tube significantly affects the tube's evolution and the rotational motions that develop at the photosphere. The rotation angle, vorticity, and current show a direct dependence on the initial field strength. We find that an increase in field strength increases the angle through which the fieldlines rotate, the length of the fieldlines extending into the atmosphere, and the magnetic energy transported to the atmosphere. This also affects the amount of residual twist in the interior. The length of the fieldlines is crucial as we predict the twist per unit length equilibrates to a lower value on longer fieldlines. No such direct dependence is found when we modify the twist of the magnetic field owing to the complex effect this has on the tension force acting on the tube. However, there is still a clear ordering in quantities such as the rotation angle, helicity, and free energy with higher initial twist cases being related to sunspots that rotate more rapidly, transporting more helicity and magnetic energy to the atmosphere.

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Spatial Relationship between Twist in Active Region Magnetic Fields and Solar Flares

Cited by 31 publications

References 26 publications

A Non-Linear Force-Free Field Model for the Evolving Magnetic Structure of Solar Filaments

A Non-Linear Force-Free Field Model for the Evolving Magnetic Structure of Solar Filaments

Magnetic properties of flare-CME productive active regions and CME speed

Sunspot rotation

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