  Solar active regions (ARs) that produce strong flares and coronal mass
ejections (CMEs) are known to have a relatively high non-potentiality and are
characterized by delta-sunspots and sheared magnetic structures. In this study,
we conduct a series of flux emergence simulations from the convection zone to
the corona and model four types of active regions that have been
observationally suggested to cause strong flares, namely the Spot-Spot,
Spot-Satellite, Quadrupole, and Inter-AR cases. As a result, we confirm that
delta-spot formation is due to the complex geometry and interaction of emerging
magnetic fields, with finding that the strong-field, high-gradient,
highly-sheared polarity inversion line (PIL) is created by the combined effect
of the advection, stretching, and compression of magnetic fields. We show that
free magnetic energy builds up in the form of a current sheet above the PIL. It
is also revealed that photospheric magnetic parameters that predict flare
eruptions reflect the stored free energy with high accuracy, while
CME-predicting parameters indicate the magnetic relationship between flaring
zones and entire ARs.
