PHOTOSPHERIC FLUX CANCELLATION AND THE BUILD-UP OF SIGMOIDAL FLUX ROPES ON THE SUN

In this study we explore the scenario of photospheric flux cancellation being the primary formation mechanism of sigmoidal flux ropes in decaying active regions. We analyze magnetogram and X-ray observations together with data-driven non-linear force-free field (NLFFF) models of observed sigmoidal r...

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Bibliographic Details
Published in:The Astrophysical journal 2012-11, Vol.759 (2), p.1-22
Main Authors: SAVCHEVA, A. S, GREEN, L. M, VAN BALLEGOOIJEN, A. A, DELUCA, E. E
Format: Article
Language:English
Subjects:
Accumulation
Arcades
ASTRONOMY
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Cancellation
Decay
Earth, ocean, space
EMISSION SPECTRA
Exact sciences and technology
Flares
Flux
FREE ENERGY
GAMMA RADIATION
MAGNETIC FIELDS
MDI
NONLINEAR PROBLEMS
PHOTOSPHERE
Poloidal flux
SOLAR CORONA
SOLAR FLARES
SUN
TOPOLOGY
X RADIATION
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Summary:In this study we explore the scenario of photospheric flux cancellation being the primary formation mechanism of sigmoidal flux ropes in decaying active regions. We analyze magnetogram and X-ray observations together with data-driven non-linear force-free field (NLFFF) models of observed sigmoidal regions to test this idea. We measure the total and canceled fluxes in the regions from MDI magnetograms, as well as the axial and poloidal flux content of the modeled NLFFF flux ropes for three sigmoids-2007 February, 2007 December, and 2010 February. We infer that the sum of the poloidal and axial flux in the flux ropes for most models amounts to about 60%-70% of the canceled flux and 30%-50% of the total flux in the regions. The flux measurements and the analysis of the magnetic field structure show that the sigmoids first develop a strong axial field manifested as a sheared arcade and then, as flux cancellation proceeds, form long S-shaped field lines that contribute to the poloidal flux. In addition, the dips in the S-shaped field lines are located at the sites of flux cancellation that have been identified from the MDI magnetograms. We find that the line-of-sight-integrated free energy is also concentrated at these locations for all three regions, which can be liberated in the process of eruption. Flare-associated brightenings and flare loops coincide with the location of the X-line topology that develops at the site of most vigorous flux cancellation.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/759/2/105