CRITERIA FOR FLUX ROPE ERUPTION: NON-EQUILIBRIUM VERSUS TORUS INSTABILITY

By P. Démoulin, G. Aulanier. 2010

214 citations recorded by the source corpus.

The coronal magnetic configuration of an active region typically evolves quietly for a few days before becoming suddenly eruptive and launching a coronal mass ejection (CME). The precise origin of the eruption is still under debate. The loss of equilibrium, or an ideal magnetohydrodynamic (MHD) instability such as torus instability are among the several mechanisms that have proposed to be responsible for the sudden eruptions. Distinct approaches have also been formulated for limited cases having circular or translation symmetry. We revisit the previous theoretical approaches setting them in the same analytical framework. The coronal field results from the contribution of a non-neutralized current channel added to a background magnetic field, which in our model is the potential field generated by two photospheric flux concentrations. The evolution on short Alfvénic timescale is governed by ideal MHD. We first show analytically that the loss of equilibrium and the stability analysis are two different views of the same physical mechanism. Second, we identify that the same physics is involved in the instabilities of circular and straight current channels. Indeed, they are just two particular limiting cases of more general current paths. A global instability of the magnetic configuration is present when the current channel is located at a coronal height, h, large enough so that the decay index of the potential field, ∂ln |Bp|/∂ln h, is larger than a critical value. At the limit of very thin current channels, previous analysis has found critical decay indices of 1.5 and 1 for circular and straight current channels, respectively. However, with current channels being deformable and as thick as that expected in the corona, we show that this critical index has similar values for circular and straight current channels, and is typically in the range [1.1,1.3].

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/059988122ea5326fd0f1db0a1ff3c7d6ba99b63e

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Citations in the corpus

The standard flare model in three dimensions II: upper limit on solar flare energy (2012, background): “The CME itself was triggered by the ideal loss-of-equilibrium of a weakly twisted coronal flux rope (Aulanier et al. 2010), corresponding to the torus instability (Kliem & Török 2006; Démoulin & Aulanier 2010).”
MAGNETIC FIELD STRUCTURES TRIGGERING SOLAR FLARES AND CORONAL MASS EJECTIONS (2012, background): “The rapid ascent of the twisted rope can be attributed to the loss of equilibrium and ideal MHD stability (Forbes & Priest 1995; Kliem & Török 2006; Démoulin & Aulanier 2010).”
The standard flare model in three dimensions - I. Strong-to-weak shear transition in post-flare loops (2012, background): “Nevertheless, it is present in electric-wire flare models, which incorporate MHD properties (Démoulin & Aulanier 2010).”