The Role of Reconnection in the Onset of Solar Eruptions

We use three dimensional magnetohydrodynamic numerical simulations to study the interaction of coronal magnetic fields with emerging flux and determine the conditions that lead to eruptive activity. We find that emerging magnetic fields produce sheared arcades that transition to coronal flux ropes, and that these structures are constrained by their own outer field. The reconnection between emerging and pre-existing coronal fields is necessary to generate sufficient expansion of the emerging structure so that flare-like reconnection below the coronal flux rope becomes strong enough to trigger its release. Our results imply that the relative orientation of emerging and pre-existing coronal fields is the key parameter in determining whether the resultant active regions exhibit eruptive behavior, and is thus a potentially useful candidate for predicting eruptions in newly emerging active regions. More generally, our results demonstrate that the detailed interaction between the convection zone/photosphere and the corona must be calculated self-consistently in order to model solar eruptions accurately.