Skin-layer of the eruptive magnetic flux rope in large solar flares


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Abstract

The analysis of observations of large solar flares made it possible to propose a hypothesis on existence of a skin-layer in magnetic flux ropes of coronal mass ejections. On the assumption that the Bohm coefficient determines the diffusion of magnetic field, an estimate of the skin-layer thickness of ~106 cm is obtained. According to the hypothesis, the electric field of ~0.01–0.1 V/cm, having the nonzero component along the magnetic field of flux rope, arises for ~5 min in the surface layer of the eruptive flux rope during its ejection into the upper corona. The particle acceleration by the electric field to the energies of ~100 MeV/nucleon in the skin-layer of the flux rope leads to their precipitation along field lines to footpoints of the flux rope. The skin-layer presence induces helical or oval chromospheric emission at the ends of flare ribbons. The emission may be accompanied by hard X-ray radiation and by the production of gamma-ray line at the energy of 2.223 MeV (neutron capture line in the photosphere). The magnetic reconnection in the corona leads to a shift of the skin-layer of flux rope across the magnetic field. The area of precipitation of accelerated particles at the flux-rope footpoints expands in this case from the inside outward. This effect is traced in the chromosphere and in the transient region as the expanding helical emission structures. If the emission extends to the spot, a certain fraction of accelerated particles may be reflected from the magnetic barrier (in the magnetic field of the spot). In the case of exit into the interplanetary space, these particles may be recorded in the Earth’s orbit as solar proton events.

About the authors

G. N. Kichigin

Institute of Solar-Terrestrial Physics, Siberian Branch

Email: syazev@gmail.com
Russian Federation, Irkutsk

L. I. Miroshnichenko

Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation; Skobeltsyn Institute of Nuclear Physics

Email: syazev@gmail.com
Russian Federation, Troitsk, Moscow; Moscow

V. I. Sidorov

Irkutsk State University

Email: syazev@gmail.com
Russian Federation, Irkutsk

S. A. Yazev

Institute of Solar-Terrestrial Physics, Siberian Branch; Irkutsk State University

Author for correspondence.
Email: syazev@gmail.com
Russian Federation, Irkutsk; Irkutsk

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