Investigation of force-freeness of a solar emerging magnetic field via application of the virial theorem to MHD simulations
Force-freeness of a solar magnetic field is a key to reconstructing the invisible coronal
magnetic structure of an emerging flux region on the Sun where active phenomena such
as flares and coronal mass ejections frequently occur. We have performed magnetohydrodynamic
simulations which are adjusted to investigate force-freeness of an emerging
magnetic field by using the virial theorem. Our focus is on how the force-free range of
an emerging flux region develops and how it depends on the twist of a pre-emerged
magnetic field. As an emerging flux region evolves, the upper limit of the force-free
range continuously increases while the lower limit is asymptotically reduced to the order
of a photospheric pressure scale height above the solar surface. As the twist becomes
small the lower limit increases and then seems to be saturated. We also discuss the
applicability of the virial theorem to an evolving magnetic structure on the Sun.
Reference
Kang, J. H. & Magara, T.
Publication of Astronomical Society of Japan, 66, 121
