Equilibrium and observational properties of line-tied twisted flux tubes

Aulanier, G.; Démoulin, P.; Grappin, R.

doi:10.1051/0004-6361:20041519

Cited by 106 publications

(138 citation statements)

References 43 publications

Supporting

Mentioning

133

Contrasting

Unclassified

Order By: Relevance

“…We use the explicit three-dimensional MHD code described in Aulanier et al (2005a), to which we add finite-β adiabatic effects. The numerical simulation is performed in a Cartesian domain in which x and y are the horizontal axes and z is the vertical axis.…”

Section: Equation and Boundary Conditionsmentioning

confidence: 99%

The Nature of Flare Ribbons in Coronal Null-Point Topology

Masson¹,

Pariat²,

Aulanier³

et al. 2009

ApJ

Self Cite

329

432

View full text Add to dashboard Cite

Flare ribbons are commonly attributed to the low-altitude impact, along the footprints of separatrices or quasiseparatrix layers (QSLs), of particle beams accelerated through magnetic reconnection. If reconnection occurs at a three-dimensional coronal magnetic null point, the footprint of the dome-shaped fan surface would map a closed circular ribbon. This paper addresses the following issues: does the entire circular ribbon brighten simultaneously, as expected because all fan field lines pass through the null point? And since the spine separatrices are singular field lines, do spine-related ribbons look like compact kernels? What can we learn from these observations about current sheet formation and magnetic reconnection in a null-point topology? The present study addresses these questions by analyzing Transition Region and Coronal Explorer and Solar and Heliospheric Observatory/Michelson Doppler Imager observations of a confined flare presenting a circular ribbon. Using a potential field extrapolation, we linked the circular shape of the ribbon with the photospheric mapping of the fan field lines originating from a coronal null point. Observations show that the flare ribbon outlining the fan lines brightens sequentially along the counterclockwise direction and that the spine-related ribbons are elongated. Using the potential field extrapolation as initial condition, we conduct a low-β resistive magnetohydrodynamics simulation of this observed event. We drive the coronal evolution by line-tied diverging boundary motions, so as to emulate the observed photospheric flow pattern associated with some magnetic flux emergence. The numerical analysis allows us to explain several observed features of the confined flare. The vorticity induced in the fan by the prescribed motions causes the spines to tear apart along the fan. This leads to formation of a thin current sheet and induces null-point reconnection. We also find that the null point and its associated topological structure is embedded within QSLs, already present in the asymmetric potential field configuration. We find that the QSL footprints correspond to the observed elongated spine ribbons. Finally, we observe that before and after reconnecting at the null point, all field lines undergo slipping and slip-running reconnection within the QSLs. Field lines, and therefore particle impacts, slip or slip-run according to their distance from the spine, in directions and over distances that are compatible with the observed dynamics of the ribbons.

show abstract

Section: Equation and Boundary Conditionsmentioning

confidence: 99%

The Nature of Flare Ribbons in Coronal Null-Point Topology

Masson¹,

Pariat²,

Aulanier³

et al. 2009

ApJ

Self Cite

329

432

View full text Add to dashboard Cite

show abstract

“…These circular vortical motions are applied at the zones of maximal B z (the foot-points), and thus are spatially coincident with the contours of the vertical field, which are approximately circular there (cf. discussions by Török & Kliem 2003;Aulanier et al 2005).…”

Section: Mhd Equations and Model Parametersmentioning

confidence: 99%

Thermal and non-thermal emission from reconnecting twisted coronal loops

Pinto

Gordovskyy

Browning

et al. 2016

A&A

View full text Add to dashboard Cite

Context. Twisted magnetic fields should be ubiquitous in the solar corona, particularly in flare-producing active regions where the magnetic fields are strongly non-potential. The magnetic energy contained in such twisted fields can be released during solar flares and other explosive phenomena. It has been shown recently that reconnection in helical magnetic coronal loops results in plasma heating and particle acceleration distributed within a large volume, including the lower coronal and chromospheric sections of the loops. Hence, the magnetic reconnection and particle acceleration scenario involving magnetic helicity can be a viable alternative to the standard flare model, where particles are accelerated only in a small volume located in the upper corona. Aims. The key goal of this study is to investigate the links and observational signatures of plasma heating and particle acceleration in kink-unstable twisted coronal loops. Methods. We use a combination of MHD simulations and test-particle methods. These simulations describe the development of kink instability and magnetic reconnection in twisted coronal loops using resistive compressible MHD, and incorporate atmospheric stratification and large-scale loop curvature. The resulting distributions of hot plasma let us estimate thermal X-ray emission intensities. The electric and magnetic fields obtained are used to calculate electron trajectories using the guiding-centre approximation. These trajectories combined with the MHD plasma density distributions let us deduce synthetic hard X-ray bremsstrahlung intensities. Results. Our simulations emphasise that the geometry of the emission patterns produced by hot plasma in flaring twisted coronal loops can differ from the actual geometry of the underlying magnetic fields. In particular, the twist angles revealed by the emission threads (soft X-ray thermal emission; SXR) are consistently lower than the field-line twist present at the onset of the kink-instability. Hard X-ray (HXR) emission due to the interaction of energetic electrons with the stratified background are concentrated at the loop foot-points in these simulations, even though the electrons are accelerated everywhere within the coronal volume of the loop. The maximum of HXR emission consistently precedes that of SXR emission, with the HXR light-curve being approximately proportional to the temporal derivative of the SXR light-curve.

show abstract

“…The eruptive flare model was calculated numerically, using the observationally driven high-order scheme magnetohydrodynamic code (OHM: Aulanier et al 2005). The calculation was performed in the pressureless resistive MHD approximation, using non-dimensionalized units, in a 251 ×251 ×231 non-uniform cartesian mesh.…”

Section: Summary Of the Non-dimensionalized Modelmentioning

confidence: 99%

The standard flare model in three dimensions

Aulanier

Démoulin

Schrijver

et al. 2012

A&A

Self Cite

192

144

View full text Add to dashboard Cite

Context. Solar flares strongly affect the Sun's atmosphere as well as the Earth's environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics. Aims. The largest solar flares observed over the past few decades have reached energies of a few times 10 32 erg, possibly up to 10 33 erg. Flares in active Sun-like stars reach up to about 10 36 erg. In the absence of direct observations of solar flares within this range, complementary methods of investigation are needed to assess the probability of solar flares beyond those in the observational record. Methods. Using historical reports for sunspot and solar active region properties in the photosphere, we scaled to observed solar values a realistic dimensionless 3D MHD simulation for eruptive flares, which originate from a highly sheared bipole. This enabled us to calculate the magnetic fluxes and flare energies in the model in a wide paramater space. Results. Firstly, commonly observed solar conditions lead to modeled magnetic fluxes and flare energies that are comparable to those estimated from observations. Secondly, we evaluate from observations that 30% of the area of sunspot groups are typically involved in flares. This is related to the strong fragmentation of these groups, which naturally results from sub-photospheric convection. When the model is scaled to 30% of the area of the largest sunspot group ever reported, with its peak magnetic field being set to the strongest value ever measured in a sunspot, it produces a flare with a maximum energy of ∼6 × 10 33 erg. Conclusions. The results of the model suggest that the Sun is able to produce flares up to about six times as energetic in total solar irradiance fluence as the strongest directly observed flare of Nov. 4, 2003. Sunspot groups larger than historically reported would yield superflares for spot pairs that would exceed tens of degrees in extent. We thus conjecture that superflare-productive Sun-like stars should have a much stronger dynamo than in the Sun.

show abstract

Equilibrium and observational properties of line-tied twisted flux tubes

Cited by 106 publications

References 43 publications

The Nature of Flare Ribbons in Coronal Null-Point Topology

The Nature of Flare Ribbons in Coronal Null-Point Topology

Thermal and non-thermal emission from reconnecting twisted coronal loops

The standard flare model in three dimensions

Contact Info

Product

Resources

About