  Current magnetohydrodynamic (MHD) simulations of the initiation of solar
eruptions are still commonly carried out with idealized magnetic field models,
whereas the realistic coronal field prior to eruptions can possibly be
reconstructed from the observable photospheric field. Using a nonlinear
force-free field extrapolation prior to a sigmoid eruption in AR 11283 as the
initial condition in a MHD model, we successfully simulate the realistic
initiation process of the eruption event, as is confirmed by a remarkable
resemblance to the SDO/AIA observations. Analysis of the pre-eruption field
reveals that the envelope flux of the sigmoidal core contains a coronal null
and furthermore the flux rope is prone to a torus instability. Observations
suggest that reconnection at the null cuts overlying tethers and likely
triggers the torus instability of the flux rope, which results in the eruption.
This kind of simulation demonstrates the capability of modeling the realistic
solar eruptions to provide the initiation process.
