Emerging flux model for the solar flare phenomenon

Journal Article · Mon Aug 15 04:00:00 EDT 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155453· OSTI ID:7219698

Heyvaerts, J; Priest, E R; Rust, D M

It is suggested that many solar flares occur in three stages when loops of magnetic flux emerge from below the photosphere and interact with the overlying field. First of all, during the preflare heating phase, continuous reconnection occurs in the current sheet that forms between the new and old flux. Waves which radiate from the ends of the sheet heat the plasma that passes through them and cause an increase in soft X-ray emission. Eventually, the emerging flux loops reach a critical height (dependent on the merging speed and magnetic field strength, but typically in the upper chromosphere), at which there is no neighboring equilibrium; the current sheet heats up, seeking a new equilibrium state, and the current density exceeds the value for the occurrence of plasma microinstabilities. Then the impulsive and flash phases take place. The onset of a turbulent electrical resistivity in the sheet causes it to expand rapidly, leading to electric fields far stronger than the Dreicer value. Particles are accelerated to high energies and escape along field lines. Those particles that follow magnetic field lines down to the low chromosphere produce H..cap alpha.. flare knots, while any which follow field lines high into the corona excite type III radio bursts. The attainment of the critical current density in the sheet may thus be regarded as the trigger for the flare. Finally, in the main phase, a new state of steady magnetic field reconnection is reached, with a much larger (marginally turbulent) current sheet than before.

• Research Organization: Observatoire de Meudon, D.A.F., Meudon, France
• OSTI ID: 7219698
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 216:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
CONVECTION
ELECTRIC FIELDS
ENERGY TRANSFER
FLUID MECHANICS
HEAT TRANSFER
HYDRODYNAMICS
MAGNETIC FIELD CONFIGURATIONS
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
MATHEMATICAL MODELS
MECHANICS
PHOTOSPHERE
PLASMA
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR FLARES
SPECTRA
STAR MODELS
TURBULENCE
X-RAY SPECTRA