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Title:
Current Paths in the Corona and Energy Release in Solar Flares
Authors:
Melrose, D. B.
Publication:
Astrophysical Journal v.451, p.391 (ApJ Homepage)
Publication Date:
09/1995
Origin:
APJ; KNUDSEN
ApJ Keywords:
MAGNETOHYDRODYNAMICS: MHD, SUN: CORONA, SUN: FLARES, SUN: MAGNETIC FIELDS
DOI:
10.1086/176228
Bibliographic Code:
1995ApJ...451..391M

Abstract

Vector magnetogram data show that (1) regions of large current flow, I ˜ 1012 A, correlate with the footpoints of flaring coronal loops, and (2) the currents flow up in a region of one magnetic polarity and down in a region of opposite magnetic polarity. It is argued that these properties imply that the currents cannot be generated by shearing or other motions near the photo sphere, and must close deep in the solar atmosphere. It is also argued that the line-tying assumption is inappropriate on timescales of 1 day or longer on which coronal magnetic structures evolve and that an appeal to line tying incorrectly implies that coronal currents close near the photo sphere. The observed shearing of coronal magnetic structures is attributed to the emergence of current-carrying magnetic flux tubes.

Energy release in a solar flare is discussed with emphasis on the nonlocal nature of changes in the stored magnetic energy. Energy release occurs in two stages, with nondissipative, local conversion of stored energy into a Poynting flux at Alfvénic fronts, and conversion into particle energy in localized energy release site. The nonlocal nature of the energy release process is described in terms of a circuit model with temporally varying parameters. The power release, IV, occurs at constant total current I ˜ 1012 A, due to a large inductive voltage, V ˜1010 V, and involves changes in the current profile or current path, described by a changing coronal inductance, L, with a coronal resistance, Rc determined by Ldot + Rc = 0. Three ways in which the net inductance can decrease are discussed: like currents moving apart, the current path shortening, and unlike currents moving closer together. Simple models for an erupting filament show that magnetic energy release can drive the eruption only if the current in the filament drains away into a current path lower in the corona. Relocation of the current to a lower height should cause the shearing near the neutral line to increase as a result of a flare, as has been reported recently.

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