Simulation of dark lanes in post-flare supra-arcades: III. A 2D simulation

Abstract

Context. Observational dark sinuous inflows moving sunwards, along a fan of rays were previously numerically reproduced with two simulations of 1.5D for the first time. We showed that the dark tracks can be explained as hot plasma voids generated upstream of a slow magnetoacoustic shock wave that is produced by a localized deposition of energy. Aims. We aim to confirm our "dark lane" interpretation and to identify specific 2D contributions to the description of the phenomenon. Methods. To solve the ideal and non-stationary MHD equations we used a 2D Riemann solver Eulerian code specially designed to capture supersonic flow discontinuities. Results. The numerical 2D results agree with the observational behaviour, but they show a slight shift in the characteristic parameter with respect to those found previously. Conclusions. We qualitatively confirm the behaviour found in previous papers. For a given numerical domain the period of the kink-like structure is a function of the magnetic field intensity: larger periods are associated with lower magnetic field intensities. Contrary to the 1.5D result - where the sunwards dynamic is independent of the magnetic field intensity owing to its exclusive waveguide role - in the 2D simulation the sunwards speed is higher for higher values of the magnetic field. This can be interpreted as the capability of the low coronal plasma to collimate the deposition of energy into the magnetic field direction. The moving features that consist on low-density and high-temperature plasma cavities have higher inside values of the structuring parameter β than the neighbouring media. Thus, the voids seem to be the emergence structures of a whole nonlinear interacting plasma context of shocks and waves instead of voided plasma loops that are magnetically structured. © 2011 ESO.