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We present the first model that couples the formation of the corona of asolar active region to a model of the emergence of a sunspot pair. This allowsus to study when, where, and why active region loops form, and how they evolve.We use a 3D radiation MHD simulation of the emergence of an active regionthrough the upper convection zone and the photosphere as a lower boundary for a3D MHD coronal model. The latter accounts for the braiding of the magneticfieldlines, which induces currents in the corona heating up the plasma. Wesynthesize the coronal emission for a direct comparison to observations.Starting with a basically field-free atmosphere we follow the filling of thecorona with magnetic field and plasma. Numerous individually identifiable hotcoronal loops form, and reach temperatures well above 1 MK with densitiescomparable to observations. The footpoints of these loops are found where smallpatches of magnetic flux concentrations move into the sunspots. The loopformation is triggered by an increase of upwards-directed Poynting flux attheir footpoints in the photosphere. In the synthesized EUV emission theseloops develop within a few minutes. The first EUV loop appears as a thin tube,then rises and expands significantly in the horizontal direction. Later, thespatially inhomogeneous heat input leads to a fragmented system of multipleloops or strands in a growing envelope.

A model for the formation of the active region corona driven by magnetic flux emergence