Invited review abstract

Large-scale emergence of magnetic flux from below the photosphere results in the formation of active regions whose lifetime can vary from days to months. Both emergence and cancellation of magnetic flux are common processes in active regions. Changes in the magnetic flux budget of an active region can destabilize the existing structures and induce large-scale dynamical events such as flares and coronal mass ejections (CMEs).
We present the results of numerical simulations that investigate the effect of flux emergence on the global solar corona. The initially stable corona consists of an ambient dipole field and a bipolar active region embedded in a streamer overlying the solar equator. The initial configuration is favourable for the breakout CME model to work. The magnetic flux of the active region is then linearly increased in time. When a sufficient amount of new flux has emerged, an eruption occurs. The speed of the CME is independent of the amount of flux emerged, and within this specific set-up the CME turns out to be the detached helmet streamer. These simulation show that whether or not the flux emergence process results in a CME is strongly dependent on the global configuration of the magnetic field. We have also demonstrated that inducing magnetic helicity is not a necessary condition in order to get an eruption of the coronal field.