3 Energy Build-up

The evolution of a flare basically starts with the emergence of magnetic field into the surface (flux emergence), which carries magnetic energy from the interior to the atmosphere. Part of this magnetic energy is immediately released when emerging magnetic field expands to form a magnetic structure on the Sun. The electric current crossing the magnetic field (cross-field current) generate the Lorentz force, so it drives expansion. The electric current flowing along magnetic field (field-aligned current), on the other hand, does not generate the Lorentz force, so the field-aligned current is not used during an expanding process. In addition to that, the field-aligned current is not easy to dissipate in a highly conductive medium such as the solar corona, so it is stored there as free energy that becomes the energy source of flares and flare-associated phenomena.

 3.1 Emergence of magnetic field (flux emergence)
  3.1.1 Morphology
  3.1.2 Dynamics
  3.1.3 Latest progress
 3.2 Magnetic structure
  3.2.1 Filament (Prominence)
  3.2.2 Sigmoid
  3.2.3 Force-free field
  3.2.4 Aly–Sturrock conjecture
 3.3 Magnetic helicity

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