  We propose a new model for the initiation of a solar coronal mass ejection
(CME). The model agrees with two properties of CMEs and eruptive flares that
have proved to be very difficult to explain with previous models. a) Very
low-lying magnetic field lines, down to the photospheric neutral line, can open
toward infinity during an eruption. b) The eruption is driven solely by
magnetic free energy stored in a closed, sheared arcade; consequently, the
magnetic energy of the closed state is well above that of the post-eruption
open state. The key new feature of our model is that CMEs occur in multi-polar
topologies, in which reconnection between a sheared arcade and neighboring flux
systems triggers the eruption. In this ``magnetic breakout'' model,
reconnection removes the unsheared field above the low-lying, sheared core flux
near the neutral line, thereby allowing this core flux to burst open. We
present numerical simulations which demonstrate that our model can account for
the energy requirements for CMEs. We discuss the implication of the model for
CME/flare prediction.
