Structure-Driven Nonlinear Instability as the Origin of the Explosive Reconnection Dynamics in Resistive Double Tearing Modes

Abstract

The onset of abrupt magnetic reconnection events, observed in the nonlinear evolution of double tearing modes (DTM), is investigated via reduced resistive magnetohydrodynamic simulations. We have identified the critical threshold for the parameters characterizing the linear DTM stability leading to the bifurcation to the explosive dynamics. A new type of secondary instability is discovered that is excited once the magnetic islands on each rational surface reach a critical structure characterized here by the width and the angle rating their triangularization. This new instability is an island structure-driven nonlinear instability, identified as the trigger of the subsequent nonlinear dynamics which couples flow and flux perturbations. This instability only weakly depends on resistivity.

Viscosity Effects on Explosive Growth Dynamics of the Nonlinear Resistive Tearing Mode

“…The nonlinear positive feedback of current sheet formation leads to explosive growth of the reconnected flux. To testify this idea, a stability analysis is carried out in a quasi-linear equilibrium involving the zonal current, which is taken directly from the nonlinear simulations [15,16]. This means that the new equilibrium, as shown in Fig.…”

Three-dimensional magnetic reconnection and its application to solar flares

“…As such, the morphology of QSLs in the presence of erupting flux ropes is independent of the extrapolation method. This is expected because of the structural stability of QSLs, in contrast to the presence and the location of null points and associated separatrices, (see Démoulin et al 1994a;Janvier et al 2016, on the influence of the extrapolations on the stability of null points and QSLs). Furthermore, the shapes of the QSLs can be directly compared with that of the flare ribbons.…”

“…Following up on this study, Janvier et al (2016) investigated the more complex flaring region of 6 September 2011 (SOL2011-09-06T22:20). This region, as shown in figure 12, shows a complex network of flare ribbons compared with a typical two-ribbon eruption.…”

“…Then, evolving the magnetic model of an active region, for example by an MHD evolution or a magnetofrictional relaxation (in the case of an unstable flux rope), also allows the investigation of the evolution of QSLs. The multiple time sequences of these evolutions can provide snapshots that can be compared with observations of flare ribbons, as presented in Savcheva et al (2015Savcheva et al ( , 2016, Janvier et al (2016).…”

“…Furthermore, multiple tearing instabilities can greatly enhance the reconnection rate in the nonlinear regime due to coupling between islands (where the reconnection outflow of a magnetic island can increase the inflow of a nearby reconnection site, e.g. Pritchett, Lee & Drake 1980;Ishii, Azumi & Kishimoto 2002;Bierwage et al 2005;Janvier, Kishimoto & Li 2011;Wang, Yokoyama & Isobe 2015). Finally the effect of line-tying, relevant in the context of coronal magnetic field, was investigated in Delzanno & Finn (2008), which found that the growth rate scaled with η for small structure lengths (compared with the system size), while it was tearing-like for long structures.…”