MHD Numerical Simulations of an Emerging Flux Tube
for studying effects of twist intensity and associated
Active Phenomena in the Solar Atmosphere
Takehiro Miyagoshi, Hiroaki Isobe, Takaaki Yokoyama, Kazunari Shibata
It is suggested that emerging flux build up magnetic energy
in the solar corona that could become
the source of flares or CMEs. Emerging flux also plays
an important role in active region formation and disappearance.
To investigate these phenomena, it is necessary to study the evolution
of an emerging flux from the convection zone to the corona.
Photosphere is gas pressure dominant (high plasma beta) region. So
a magnetic flux tube in there could have some twists.
To study emerging process of twisted flux tube, three dimensional
MHD simulation is necessary.
However, in almost all past numerical simulations for studying emerging process
of twisted flux tube from convection zone to the upper corona,
very strong twist
(more than one times round in half wavelength at initial state)
is approximated.
On the other hand, from observation, more weak twist flux tubes are often seen.
So in this paper we will show the results of our three-dimensional MHD
simulations of emergence of a twisted flux tube for studying effects of
twist intensity, especially for weak twist case. We found that
in weak twist case (including no
twist case), a tube fragments once around the photosphere, and
is extended to horizontal direction. Then emerging motion is
rapidly suppressed. However,
new emergence starts after fragmented magnetic field
and continuously emerged flux from the bottom of the tube
filling the solar surface. Also magnetic energy brought into the corona by
emerging flux tube depends on twist intensity.
We will also show that active phenomena, jet or surge caused by interaction
between emerging flux tube and overlying active region magnetic fields.
Correspondence
Takehiro Miyagoshi (miyagosi@kwasan.kyoto-u.ac.jp), Kwasan Observatory, Kyoto University
presentation
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