Coronal Mass Ejection: Initiation, Magnetic Helicity, and Flux Ropes. I. Boundary Motion–driven Evolution

Amari, T.; Luciani, J. F.; Aly, J. J.; Mikić, Z.; Linker, J. A.

doi:10.1086/345501

Cited by 279 publications

(230 citation statements)

References 35 publications

Supporting

Mentioning

217

Contrasting

Order By: Relevance

“…There, the amount of energy associated with the magnetic field is much larger than other energy sources, and the dynamics of the coronal configuration is determined by the evolution of its magnetic field (e.g., Forbes 2000). This includes solar flares, where large currents develop in relatively small volumes (e.g., Shibata & Magara 2011;Aulanier et al 2012), and coronal mass ejections (CMEs), which are powerful expulsions of coronal material that change the local configuration of the magnetic field drastically (e.g., Forbes 2000; Amari et al 2003;Fan 2010). In the coronal plasma, the magnetic energy is therefore the prime energy reservoir that fuels the dynamical evolution of these events.…”

Section: Introductionmentioning

confidence: 99%

Accuracy of magnetic energy computations

Valori

Démoulin

Pariat

et al. 2013

A&A

118

View full text Add to dashboard Cite

Context. For magnetically driven events, the magnetic energy of the system is the prime energy reservoir that fuels the dynamical evolution. In the solar context, the free energy (i.e., the energy in excess of the potential field energy) is one of the main indicators used in space weather forecasts to predict the eruptivity of active regions. A trustworthy estimation of the magnetic energy is therefore needed in three-dimensional (3D) models of the solar atmosphere, e.g., in coronal fields reconstructions or numerical simulations. Aims. The expression of the energy of a system as the sum of its potential energy and its free energy (Thomson's theorem) is strictly valid when the magnetic field is exactly solenoidal. For numerical realizations on a discrete grid, this property may be only approximately fulfilled. We show that the imperfect solenoidality induces terms in the energy that can lead to misinterpreting the amount of free energy present in a magnetic configuration. Methods. We consider a decomposition of the energy in solenoidal and nonsolenoidal parts which allows the unambiguous estimation of the nonsolenoidal contribution to the energy. We apply this decomposition to six typical cases broadly used in solar physics. We quantify to what extent the Thomson theorem is not satisfied when approximately solenoidal fields are used. Results. The quantified errors on energy vary from negligible to significant errors, depending on the extent of the nonsolenoidal component of the field. We identify the main source of errors and analyze the implications of adding a variable amount of divergence to various solenoidal fields. Finally, we present pathological unphysical situations where the estimated free energy would appear to be negative, as found in some previous works, and we identify the source of this error to be the presence of a finite divergence. Conclusions. We provide a method of quantifying the effect of a finite divergence in numerical fields, together with detailed diagnostics of its sources. We also compare the efficiency of two divergence-cleaning techniques. These results are applicable to a broad range of numerical realizations of magnetic fields.

show abstract

Section: Introductionmentioning

confidence: 99%

Accuracy of magnetic energy computations

Valori

Démoulin

Pariat

et al. 2013

A&A

118

View full text Add to dashboard Cite

show abstract

“…Savcheva et al (2012) explain the formation of an observed flux rope due to the rotation of the foot points of an active region in the presence of magnetic diffusion. While in Amari et al (2003) the flux rope is formed (and then ejected) as a result of shearing followed by flux cancellation. In addition to these studies, the ejection of flux ropes may be explained by several mechanisms in numerical models: Török & Kliem (2005, Fan (2010) and Aulanier et al (2010) use the Torus instability as the main driver for a full ejection.…”

Section: Introductionmentioning

confidence: 99%

Magnetohydrodynamic simulations of the ejection of a magnetic flux rope

Pagano

Mackay

Poedts

2013

A&A

View full text Add to dashboard Cite

Context. Coronal mass ejections (CME's) are one of the most violent phenomena found on the Sun. One model to explain their occurrence is the flux rope ejection model. In this model, magnetic flux ropes form slowly over time periods of days to weeks. They then lose equilibrium and are ejected from the solar corona over a few hours. The contrasting time scales of formation and ejection pose a serious problem for numerical simulations. Aims. We simulate the whole life span of a flux rope from slow formation to rapid ejection and investigate whether magnetic flux ropes formed from a continuous magnetic field distribution, during a quasi-static evolution, can erupt to produce a CME. Methods. To model the full life span of magnetic flux ropes we couple two models. The global non-linear force-free field (GNLFFF) evolution model is used to follow the quasi-static formation of a flux rope. The MHD code ARMVAC is used to simulate the production of a CME through the loss of equilibrium and ejection of this flux rope. Results. We show that the two distinct models may be successfully coupled and that the flux rope is ejected out of our simulation box, where the outer boundary is placed at 2.5 R . The plasma expelled during the flux rope ejection travels outward at a speed of 100 km s −1 , which is consistent with the observed speed of CMEs in the low corona. Conclusions. Our work shows that flux ropes formed in the GNLFFF can lead to the ejection of a mass loaded magnetic flux rope in full MHD simulations. Coupling the two distinct models opens up a new avenue of research to investigate phenomena where different phases of their evolution occur on drastically different time scales.

show abstract

“…The CME models involve the eruption of a flux rope either by magnetic reconnection or by magnetohydrodynamic (MHD) instabilities. For example, an emerging flux trigger (Chen & Shibata 2000), flux cancellation (Amari et al 2003a(Amari et al ,b, 2010, tether cutting (Moore et al 2001), and breakout models (Antiochos et al 1999;Lynch et al 2004;Karpen et al 2012) require magnetic reconnection below or above the flux rope. On the other hand, numerical MHD simulations of the kink instability suggest that if the twist of the flux rope exceeds a critical value (∼1.75 field line turns), then it becomes unstable (Fan & Gibson 2003Kliem et al 2004;Török & Kliem 2003;Török et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength observation of a large-scale flux rope eruption above a kinked small filament

Kumar

Cho

2014

A&A

View full text Add to dashboard Cite

We analyzed multiwavelength observations of a western limb flare (C3.9) that occurred in AR NOAA 111465 on 30 April 2012. The high-resolution images recorded by SDO/AIA 304, 1600 Å and Hinode/SOT Hα show the activation of a small filament (rising speed ∼ 40 km s −1 ) associated with a kink instability and the onset of a C-class flare near the southern leg of the filament. The first magnetic reconnection occurred at one of the footpoints of the filament and caused the breaking of its southern leg. The filament shows unwinding motion of the northern leg and apex in counterclockwise direction and failed to erupt. A flux-rope structure (visible only in hot channels, i.e., AIA 131 and 94 Å and Hinode/SXT) appeared along the neutral line during the second magnetic reconnection that occurred above the kinked filament. The formation of the RHESSI hard X-ray source (12−25 keV) above the kinked filament and the simultaneous appearance of the hot 131 Å loops associated with photospheric brightenings (AIA 1700 Å) indicates the particle acceleration along these loops from the top of the filament. In addition, extreme ultraviolet disturbances or waves observed above the filament in 171 Å also show a close association with magnetic reconnection. The flux rope rises slowly (∼100 km s −1 ), which produces a very large twisted structure possibly through reconnection with the surrounding sheared magnetic fields within ∼15−20 min, and showed an impulsive acceleration reaching a height of about 80-100 Mm. AIA 171 and SWAP 174 Å images reveal a cool compression front (or coronal mass ejection frontal loop) surrounding the hot flux rope structure.

show abstract

Coronal Mass Ejection: Initiation, Magnetic Helicity, and Flux Ropes. I. Boundary Motion–driven Evolution

Cited by 279 publications

References 35 publications

Accuracy of magnetic energy computations

Accuracy of magnetic energy computations

Magnetohydrodynamic simulations of the ejection of a magnetic flux rope

Multiwavelength observation of a large-scale flux rope eruption above a kinked small filament

Contact Info

Product

Resources

About