Flare-productive active regions. (arXiv:1904.12027v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Toriumi_S/0/1/0/all/0/1">Shin Toriumi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_H/0/1/0/all/0/1">Haimin Wang</a>
Strong solar flares and coronal mass ejections, here defined not only as the
bursts of electromagnetic radiation but as the entire process in which magnetic
energy is released through magnetic reconnection and plasma instability,
emanate from active regions (ARs) in which high magnetic non-potentiality
resides in a wide variety of forms. This review focuses on the formation and
evolution of flare-productive ARs from both observational and theoretical
points of view. Starting from a general introduction of the genesis of ARs and
solar flares, we give an overview of the key observational features during the
long-term evolution in the pre-flare state, the rapid changes in the magnetic
field associated with the flare occurrence, and the physical mechanisms behind
these phenomena. Our picture of flare-productive ARs is summarized as follows:
subject to the turbulent convection, the rising magnetic flux in the interior
deforms into a complex structure and gains high non-potentiality; as the flux
appears on the surface, an AR with large free magnetic energy and helicity is
built, which is represented by delta-sunspots, sheared polarity inversion
lines, magnetic flux ropes, etc; the flare occurs when sufficient magnetic
energy has accumulated, and the drastic coronal evolution affects magnetic
fields even in the photosphere. We show that the improvement of observational
instruments and modeling capabilities has significantly advanced our
understanding in the last decades. Finally, we discuss the outstanding issues
and future perspective and further broaden our scope to the possible
applications of our knowledge to space-weather forecasting, extreme events in
history, and corresponding stellar activities.
Strong solar flares and coronal mass ejections, here defined not only as the
bursts of electromagnetic radiation but as the entire process in which magnetic
energy is released through magnetic reconnection and plasma instability,
emanate from active regions (ARs) in which high magnetic non-potentiality
resides in a wide variety of forms. This review focuses on the formation and
evolution of flare-productive ARs from both observational and theoretical
points of view. Starting from a general introduction of the genesis of ARs and
solar flares, we give an overview of the key observational features during the
long-term evolution in the pre-flare state, the rapid changes in the magnetic
field associated with the flare occurrence, and the physical mechanisms behind
these phenomena. Our picture of flare-productive ARs is summarized as follows:
subject to the turbulent convection, the rising magnetic flux in the interior
deforms into a complex structure and gains high non-potentiality; as the flux
appears on the surface, an AR with large free magnetic energy and helicity is
built, which is represented by delta-sunspots, sheared polarity inversion
lines, magnetic flux ropes, etc; the flare occurs when sufficient magnetic
energy has accumulated, and the drastic coronal evolution affects magnetic
fields even in the photosphere. We show that the improvement of observational
instruments and modeling capabilities has significantly advanced our
understanding in the last decades. Finally, we discuss the outstanding issues
and future perspective and further broaden our scope to the possible
applications of our knowledge to space-weather forecasting, extreme events in
history, and corresponding stellar activities.
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