Coronal dynamics driven by magnetic flux emergence

To understand the built-up of the corona during the formation of the active region through magnetic flux emergence in the photosphere, we use the output of a magnetic flux emergence simulation to drive a magnetohydrodynamics (MHD) simulation for the corona. The proper treatment on the energy balance, as in the real corona, allows the model to synthesise EUV emission directly comparable to observations. In the coronal model numerous bright coronal EUV loops form during the formation of a sunspot pair in the model photosphere. The coronal loops are rooted at the outer edge of the sunspots, where an enhanced upward Poynting flux is produced by the interaction of flows and magnetic field structures. The thermal dynamics and energetics of the plasma in individual magnetic fieldlines are consistent with the expectation of traditional one dimensional loop models with prescribed heat input. At each instance of time, EUV loops are along magnetic field lines. However, their temporal evolution can be radically different. When the footpoints of emerging magnetic fieldlines consecutively move through a spot of enhanced energy input at the outer edge of the sunspot, an apparently static EUV structure is created by the plasma in the emerging magnetic fieldlines. This model highlights the power of realistic three dimensional models to resemble features in the real corona. It also emphasises the essential necessity of treating the plasma and the magnetic field at the same time, in order to self-consistently model dynamics of the coronal plasma.