  Understanding the early evolution of coronal mass ejections (CMEs), in
particular their initiation, is the key to forecasting solar eruptions and
induced disastrous space weather. Although many initiation mechanisms have been
proposed, a full understanding of CME initiation, which is identified as a slow
rise of CME progenitors in kinematics before the impulsive acceleration,
remains elusive. Here, with a state-of-the-art thermal-magnetohydrodynamics
simulation, we determine a complete CME initiation route in which multiple
mainstream mechanisms occur in sequence yet are tightly coupled. The slow rise
is first triggered and driven by the developing hyperbolic flux tube (HFT)
reconnection. Subsequently, the slow rise continues as driven by the coupling
of the HFT reconnection and the early development of torus instability. The end
of the slow rise, i.e., the onset of the impulsive acceleration, is induced by
the start of the fast magnetic reconnection coupled with the torus instability.
These results unveil that the CME initiation is a complicated process involving
multiple physical mechanisms, thus being hardly resolved by a single initiation
mechanism.
