  We clarify a relationship of the dynamics of a solar flare and a growing
Coronal Mass Ejection (CME) by investigating the dynamics of magnetic fields
during the X2.2-class flare taking place in the solar active region 11158 on
2011 February 15, based on simulation results obtained from Inoue et al. 2014.
We found that the strongly twisted lines formed through the tether-cutting
reconnection in the twisted lines of a nonlinear force-free field (NLFFF) can
break the force balance within the magnetic field, resulting in their launch
from the solar surface. We further discover that a large-scale flux tube is
formed during the eruption as a result of the tether-cutting reconnection
between the eruptive strongly twisted lines and these ambient weakly twisted
lines. Then the newly formed large flux tube exceeds the critical height of the
torus instability. The tether-cutting reconnection thus plays an important role
in the triggering a CME. Furthermore, we found that the tangential fields at
the solar surface illustrate different phases in the formation of the flux tube
and its ascending phase over the threshold of the torus instability. We will
discuss about these dynamics in detail.
