Coronal mass ejections as loss of confinement of kinked magnetic flux ropes

We perform MHD simulations in a spherical geometry of the evolution of the three-dimensional coronal magnetic field as a twisted magnetic flux tube emerges slowly into the low-β corona previously occupied by a potential arcade. We study the evolution of the emerged flux rope in the corona as its twist and magnetic energy increases due to flux emergence. We find two distinct stages of the evolution. The earlier evolution is nearly quasi-static, with the flux rope being able to settle into an neighboring equilibrium when the emergence is stopped. When the twist in the emerged flux rope reaches some critical level, the flux rope is found to undergo kink motion and erupt through the arcade field at a localized region, with most of the arcade field remaining closed. The nonlinear evolution of the kink instability facilitates the loss of confinement of the flux rope by changing its orientation at the apex such that it becomes easier for the flux rope to part and erupt through the arcade. The eruption of the writhing flux rope produces prominence field with Λ-shaped and cross-legged morphologies that have been seen in the cores of some CMEs.