Numerical Simulations of Coronal Heating Through Footpoint Braiding

Abstract

Advanced 3D radiative MHD simulations now reproduce many properties of the outer solar atmosphere. When including a domain from the convection zone into the corona, a hot chromosphere and corona are self-consistently maintained. Here we study two realistic models, with different simulated area, magnetic field strength and topology, and numerical resolution. These are compared in order to characterize the heating in the 3D-MHD simulations which self-consistently maintains the structure of the atmosphere. We analyze the heating at both large and small scales and find that heating is episodic and highly structured in space, but occurs along loop shaped structures, and moves along with the magnetic field. On large scales we find that the heating per particle is maximal near the transition region and that widely distributed opposite-polarity field in the photosphere leads to a greater heating scale height in the corona. On smaller scales, heating is concentrated in current sheets, the thicknesses of which are set by the numerical resolution. Some current sheets fragment in time, this process occurring more readily in the higher-resolution model leading to spatially highly intermittent heating. The large scale heating structures are found to fade in less than about five minutes, while the smaller, local, heating shows time scales of the order of 2 minutes in one model and 1 minutes in the other, higher-resolution, model.

3d MHD Modeling of Twisted Coronal Loops

“…Since here we address mostly the coronal evolution, the heating is assumed (in common with some previous simulations) to be active in the corona only, just because otherwise the magnetic field in the chromosphere is rapidly dissipated and we have found no way to refurbish it. Our single-loop study supports other findings from MHD modeling of solar atmosphere boxes (e.g., Hansteen et al 2015), and provides fine details. We start from a tenuous and cool atmosphere.…”

“…This approach is able to describe the formation and powering of coronal loops in a qualitative or semi-quantitative way (Gudiksen & Nordlund 2005a;Bingert & Peter 2011), including the emergence of flux tubes by magnetic twisting (Martínez-Sykora et al 2008, 2009, so as to reproduce several observed features, such as a constant cross-section (Peter & Bingert 2012), and to help interpret and use data analysis tools . Recent work has supported episodic and structured heating due to the fragmentation of current sheets and/or turbulent cascades (Hansteen et al 2015;Dahlburg et al 2016).…”

A Three-dimensional Magnetohydrodynamic Simulation of the Formation of Solar Chromospheric Jets with Twisted Magnetic Field Lines

“…As discussed above, we do not find tall chromospheric jets, like Jet-A, at a lower spatial resolution. Hansteen et al (2015) obtained results with different grid sizes and showed that the chromospheric material is more elongated for a finer spatial grid. The treatment of the radiative cooling is also a possible cause of the difference.…”

Two-dimensional Radiative Magnetohydrodynamic Simulations of Partial Ionization in the Chromosphere. II. Dynamics and Energetics of the Low Solar Atmosphere

“…Previous 2D MHD simulations (Heggland et al 2011;Leenaarts et al 2011;Iijima & Yokoyama 2015;Nóbrega-Siverio et al 2016) have required a hot plate at the upper boundary in order to produce a hot corona. Previously it was only when computing 3D models that self-consistently heated coronae arose (e.g.,Gudiksen & Nordlund 2002; Hansteen et al 2010Hansteen et al , 2015Martínez-Sykora et al 2011;Carlsson et al 2016). In the current simulations, we find that despite the 2D limitation, the large-scale magnetic field configuration in the current simulation leads to a selfconsistently heated corona.…”