Currents and their dissipation mechanism in a solar coronal MHD model

Abstract:

Magnetic features, such as flux tubes, are observed to emerge from the photosphere and rise through the solar atmosphere. This causes global reconfiguration of the magnetic connectivity and hence induces currents that are eventually dissipated. How fast the reconnection may happen and if it leads to intermittent or continuous heating (nanoflares versus magnetic diffusion) is a question still under debate. Our 3D-MHD model resembles well an observed active region, featuring loops raising with a speed of about 2 km/s, which already gives hints to the real reconnection rate. The model implements magnetic-field braiding by photospheric driving of the field lines together with a realistic energy balance. While in MHD the dissipation mechanism is assumed by a simple diffusion equation, kinetic PIC simulation allow to test for this assumption well below the spatial scales resolved by MHD-processes. We try to bridge this gap with two-fold simulations: a realistic MHD corona together with a realistic electron diffusion region in a simple reconnection setup. Our MHD model supports the slow Ohmic dissipation of currents that are induced by the slow reconfiguration of the magnetic field, while our PIC model gives hints on the correctness of the assumptions we made for the MHD model.