The Cool Surge Following Flux Emergence in a Radiation-MHD Experiment

Abstract

Cool and dense ejections, typically Hα surges, often appear alongside EUV or X-Ray coronal jets as a result of the emergence of magnetized plasma from the solar interior. Idealized numerical experiments explain those ejections as being indirectly associated with the magnetic reconnection taking place between the emerging and preexisting systems. However, those experiments miss basic elements that can importantly affect the surge phenomenon. In this paper we study the cool surges using a realistic treatment of the radiation transfer and material plasma properties. To that end, the Bifrost code is used, which has advanced modules for the equation of state of the plasma, photospheric and chromospheric radiation transfer, heat conduction and optically thin radiative cooling. We carry out a 2.5D experiment of the emergence of magnetized plasma through (meso)granular convection cells and the low atmosphere to the corona. Through detailed Lagrange tracing, we study the formation and evolution of the cool ejection and, in particular, the role of the entropy sources: this allows us to discern families of evolutionary patterns for the plasma elements. In the launch phase many elements suffer accelerations well in excess of gravity; when nearing the apex of their individual trajectories, instead, the plasma elements follow quasi-parabolic trajectories with acceleration close to g . We show how the formation of the cool ejection is mediated by a wedge-like structure composed of two shocks, one of which leads to the detachment of the surge from the original emerged plasma dome.

The Eruption of a Small-scale Emerging Flux Rope as the Driver of an M-class Flare and of a Coronal Mass Ejection

“…For instance, Archontis & Hood (2013) presented three-dimensional magnetohydrodynamics (MHD) simulations of the formation of jets triggered by the emergence and eruption of solar magnetic fields. The similar triggering process of jet and surge were obtained by simulations of Moreno-Insertis & Galsgaard (2013) and Nóbrega-Siverio et al (2016). Leake et al (2014) performed three-dimensional MHD simulations of the emergence of flux tubes from the convection zone into a preexisting dipole coronal field.…”

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

“…Despite the fact that the simulations are 2D, the corona is self-consistently maintained well above a million degrees. Previous 2D simulations required a hot plate at the top boundary in order to maintain a milliondegree corona (e.g., Heggland et al 2011;Leenaarts et al 2011;Iijima & Yokoyama 2015;Nóbrega-Siverio et al 2016). It was necessary to expand into three dimensions and have closed field lines, i.e., loops, in order to obtain a selfmaintained hot corona (e.g., Gudiksen & Nordlund 2002Hansteen et al 2010;Martínez-Sykora et al 2011;Carlsson et al 2016).…”

“…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).…”

Surges and Si iv Bursts in the Solar Atmosphere: Understanding IRIS and SST Observations through RMHD Experiments

“…Those instruments provide high-resolution observations that cover chromospheric and transition region lines, which are essential for this study. Theoretical support is given by 2.5D numerical experiments similar to the one discussed in detail by Nóbrega-Siverio et al (2016, but extending the Bifrost code capabilities (Gudiksen et al 2011) by including a module developed by Olluri et al (2013b) that calculates the ionization state of the Si IV in nonequilibrium (NEQ).…”