  We carry out a three-dimensional magneto-hydrodynamic (MHD) simulation to
model the initiation of the coronal mass ejection (CME) on 13 December 2006 in
the emerging {\delta}-sunspot active region NOAA 10930. The setup of the
simulation is similar to a previous simulation by Fan (2011), but with a
significantly widened simulation domain to accommodate the wide CME. The
simulation shows that the CME can result from the emergence of a east-west
oriented twisted flux rope whose positive, following emerging pole corresponds
to the observed positive rotating sunspot emerging against the southern edge of
the dominant pre-existing negative sunspot. The erupting flux rope in the
simulation accelerates to a terminal speed that exceeds 1500 km/s and undergoes
a counter-clockwise rotation of nearly 180 degrees such that its front and
flanks all exhibit southward directed magnetic fields, explaining the observed
southward magnetic field in the magnetic cloud impacting the Earth. With
continued driving of flux emergence, the source region coronal magnetic field
also shows the reformation of a coronal flux rope underlying the flare current
sheet of the erupting flux rope, ready for a second eruption. This may explain
the build up for another X-class eruptive flare that occurred the following day
from the same region.
