Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Yang, Shangbin; Zhang, H.; Büchner, Jörg

doi:10.1051/0004-6361/200810032

Cited by 31 publications

(20 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Eq. (8)) comprised between 0.01 and 0.1 (LaBonte et al 2007;Jeong & Chae 2007;Tian & Alexander 2008;Yang et al 2009;Démoulin & Pariat 2009) which is several times smaller than the values obtained here. The emerging structure in the present simulation is thus injecting more twist into the coronal domain than typical active regions do.…”

Section: Conclusion and Discussioncontrasting

confidence: 79%

Relative magnetic helicity as a diagnostic of solar eruptivity

Pariat

Leake

Valori³

et al. 2017

A&A

106

153

View full text Add to dashboard Cite

Context. The discovery of clear criteria that can deterministically describe the eruptive state of a solar active region would lead to major improvements on space weather predictions. Aims. Using series of numerical simulations of the emergence of a magnetic flux rope in a magnetized coronal, leading either to eruptions or to stable configurations, we test several global scalar quantities for the ability to discriminate between the eruptive and the non-eruptive simulations. Methods. From the magnetic field generated by the three-dimensional magnetohydrodynamical simulations, we compute and analyze the evolution of the magnetic flux, of the magnetic energy and its decomposition into potential and free energies, and of the relative magnetic helicity and its decomposition. Results. Unlike the magnetic flux and magnetic energies, magnetic helicities are able to markedly distinguish the eruptive from the non-eruptive simulations. We find that the ratio of the magnetic helicity of the current-carrying magnetic field to the total relative helicity presents the highest values for the eruptive simulations, in the pre-eruptive phase only. We observe that the eruptive simulations do not possess the highest value of total magnetic helicity. Conclusions. In the framework of our numerical study, the magnetic energies and the total relative helicity do not correspond to good eruptivity proxies. Our study highlights that the ratio of magnetic helicities diagnoses very clearly the eruptive potential of our parametric simulations. Our study shows that magnetic-helicity-based quantities may be very efficient for the prediction of solar eruptions.

show abstract

Section: Conclusion and Discussioncontrasting

confidence: 79%

Relative magnetic helicity as a diagnostic of solar eruptivity

Pariat

Leake

Valori³

et al. 2017

A&A

106

153

View full text Add to dashboard Cite

show abstract

“…Its sum over the emergence phase, normalized by the maximum magnetic flux to the second power, provides an estimation of the number of turns (of an equivalent uniformly twisted flux-tube). These estimations range from a few times 0.01 to a maximum value just above 0.1 (Nindos, Zhang, and Zhang, 2003;Liu and Zhang, 2006;Jeong and Chae, 2007;LaBonte, Georgoulis, and Rust, 2007;Tian and Alexander, 2008;Yang, Zhang, and Büchner, 2009). The magnetic helicity contained at a given time in the coronal field can also be estimated from magnetic-field extrapolations of the photospheric magnetograms, using the force-free model that best fits the observed coronal loops.…”

Section: Resultsmentioning

confidence: 96%

Evidence of Twisted Flux-Tube Emergence in Active Regions

et al. 2014

View full text Add to dashboard Cite

Elongated magnetic polarities are observed during the emergence phase of bipolar active regions (ARs). These extended features, called magnetic "tongues", are interpreted as a consequence of the azimuthal component of the magnetic flux in the toroidal flux-tubes that form ARs. We develop a new systematic and user-independent method to identify AR tongues. Our method is based on the determination and analysis of the evolution of the AR main polarity inversion line (PIL). The effect of the tongues is quantified by measuring the acute angle [τ ] between the orientation of the PIL and the direction orthogonal to the AR main bipolar axis. We apply a simple model to simulate the emergence of a bipolar AR. This model lets us interpret the effect of magnetic tongues on parameters that characterize ARs (e.g. the PIL inclination, and the tilt angles and their evolution). In this, idealized kinematic emergence model, τ is a monotonically increasing function of the twist and has the same sign as the magnetic helicity. We systematically apply our procedure to a set of bipolar ARs (41 ARs) that were observed emerging in line-of-sight magnetograms over eight years. For the majority of the cases studied, the presence of tongues has a small influence on the AR tilt angle since tongues have much lower magnetic flux than the more concentrated main polarities. From the observed evolution of τ , corrected by the temporal evolution of the tilt angle and its final value when the AR is fully emerged, we estimate the average number of turns present in the subphotospheric emerging flux-rope. These values for the 41 observed ARs, except one, are below unity. This indicates that sub-photospheric flux-ropes typically have a low amount of twist, i.e. highly twisted flux-tubes are rare. Our results demonstrate that the evolution of the PIL is a robust indicator of the presence of tongues and constrains the amount of twist present in emerging flux-tubes.

show abstract

“…As Holder et al (2004) remark, Tian et al (2001) did not take out the mutual latitudinal dependence between twist and tilt, and therefore any signatures of writhing could have been suppressed in their data set. Nandy (2006), further analysing the dataset used by Holder et al (2004), as well as Yang et al (2009), analysed the twist-tilt relationship. For further details, see Section 3.4.…”

Section: Tilt Anglementioning

confidence: 99%

“…Luoni et al (2011) determined the helicity sign of 40 active regions during the emergence phase as inferred from the shape of the AR's magnetic tongues and found that 63% of southern hemisphere active regions follow the hemispheric trend and only 57% of regions in the northern hemisphere do. Yang et al (2009) found that 57.6% (56%) of emerging active regions in the southern (northern) hemisphere follow the helicity trend when using the method of Chae et al (2001) to determine the helicity of the region. In a study that involved a broader spectrum of active regions (not only emerging active regions), Pevtsov et al (1995) used the linear force-free field alpha-coefficient to determine the sign of helicity and found a stronger hemispheric helicity trend where 69% (75%) of northern (southern) regions had negative (positive) helicity.…”

Section: Magnetic Helictymentioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

266

131

View full text Add to dashboard Cite

The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

show abstract

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Cited by 31 publications

References 46 publications

Relative magnetic helicity as a diagnostic of solar eruptivity

Relative magnetic helicity as a diagnostic of solar eruptivity

Evidence of Twisted Flux-Tube Emergence in Active Regions

Evolution of Active Regions

Contact Info

Product

Resources

About