Authors: Xianyu Liu (University of Michigan), Spiro Antiochos (University of Michigan), Igor Sokolov (University of Michigan), Tamas Gombosi (University of Michigan), Lulu Zhao (University of Michigan))

Several mechanisms have been proposed to explain solar coronal mass ejections (CMEs). How to distinguish these mechanisms observationally still remains an open question. This work aims to address this question by using a magnetohydrodynamic (MHD) simulations of a CME. The simulation employs the Alfv{\’e}n Wave turbulence-based Solar atmosphere Model, modified Titov-D{\’e}moulin flux rope, and the STatistical Injec\igor{T(t)}ion of Condensed Helicity (STITCH) model. The solar magnetic field is assumed to consist of two magnetic dipoles, one for the global averaged solar magnetic field and the other for a bi-polar active region. Starting from a steady-state solar corona, we superpose a flux rope and follow its relaxation toward MHD equilibrium, then apply STITCH, and study the CME eruption that results. We calculate and analyze the decay index and the twist of the flux rope. The analysis shows that the torus instability occurs at the early stage of the eruption, while there is no clear evidence of the kink instability. By tracing the field lines and analyzing the evolution of the field line lengths at different moments, we determine the onset time of the reconnection. We conclude that it is the torus instability which triggers the CME eruption. The synthetic EUV images are presented, while the related analysis is yet to be given. Our future work will include more trigger mechanisms and comparisons.