Observationally driven 3D MHD model of the solar corona above a magnetically active region

Abstract

Context: The corona of the Sun can be observed since 1932 with instruments occulting the solar disc. Only few years later it became clear that the corona is way hotter than the visible solar surface and since then, the coronal heating mechanism is unclear. So far, many processes have been proposed that are able to deliver enough energy to the base of the corona, but no complete and consistent picture of the energy transport and its localized dissipation in the corona is established. Aims: We aim for a self-consistent model of driving motions at the solar surface that bend and braid the magnetic field in the corona and produce heat by Ohmic dissipation of induced currents. We want to justify our model description by deducing synthetic observations that we check against real observations. Methods: We use observations of the magnetic field in the photosphere, as well as horizontal photospheric motions to drive our 3D MHD model. Field-aligned heat conduction and radiative losses allow for a realistic coronal energy balance. We deduce synthetic spectra in different emission lines with an atomic database using the computed coronal plasma temperature and density. These we compare with the corresponding observations of the corona above the same active region that we used for the driving. We compare samples of field lines extracted from the model corona with empirical and theoretical scaling laws predicting the coronal heating along loops. Results: Hot coronal loops of temperatures well above 1 MK form in the model corona. Their 3D structure matches the observed coronal loops and coronal Doppler shift maps indicate similar plasma flows within the observed and the model loops. With a fit to the model data, we find a scaling law that relates to the loop length and its foot-point magnetic flux density. Conclusions: From the substantial match between our model and the observed corona, we conclude that the model provides a sufficient description of the heat input and conduction along coronal loops to explain diverse observations.