Trigger Mechanism of Solar Flares in
Magnetic Arcade of Reversed Magnetic Shear

K. Kusano (Hiroshima University)

We investigated the possibility that magnetic reconnection
between the oppositely sheared magnetic loops works as a
trigger mechanism of solar flares, based on the three-dimensional
numerical simulations. The simulations were carried out by applying
a slow foot-point motion, which reverses the pre-loaded magnetic shear
in a magnetic arcade. As a result, it is clearly
demonstrated that the reversal of magnetic shear can cause a large
scale eruption of the magnetic arcade through a series of two
different kinds of magnetic reconnections.
The first reconnection is initiated by the resistive tearing mode
instability growing on the magnetic shear inversion layer.
As a consequence that the first reconnection annihilates the reversed shear,
the magnetic arcade collapses into the reconnection point, and the new
current sheet is generated above and below the shear inversion layer.
The generation of new current sheets is followed by another magnetic
reconnection, which drives the eruption of the sheared magnetic arcade.
Based on the simulation results, we finally propose a new model of flare
triggering mechanism, in which the explosive property
of flare is well explained by mutual excitation of two reconnections.