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The Astrophysical Journal, 708:314333, 2010 January 1 doi:10.1088/0004-637X/708/1/314 C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
 

Summary: The Astrophysical Journal, 708:314­333, 2010 January 1 doi:10.1088/0004-637X/708/1/314
C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
FORMATION OF TORUS-UNSTABLE FLUX ROPES AND ELECTRIC CURRENTS IN ERUPTING SIGMOIDS
G. Aulanier1
, T. T¨or¨ok1
, P. D´emoulin1
, and E. E. DeLuca2
1 LESIA, Observatoire de Paris, CNRS, UPMC, Universit´e Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02139, USA
Received 2009 June 26; accepted 2009 November 10; published 2009 December 10
ABSTRACT
We analyze the physical mechanisms that form a three-dimensional coronal flux rope and later cause its eruption.
This is achieved by a zero- magnetohydrodynamic (MHD) simulation of an initially potential, asymmetric bipolar
field, which evolves by means of simultaneous slow magnetic field diffusion and sub-Alfv´enic, line-tied shearing
motions in the photosphere. As in similar models, flux-cancellation-driven photospheric reconnection in a bald-patch
(BP) separatrix transforms the sheared arcades into a slowly rising and stable flux rope. A bifurcation from a BP to a
quasi-separatrix layer (QSL) topology occurs later on in the evolution, while the flux rope keeps growing and slowly
rising, now due to shear-driven coronal slip-running reconnection, which is of tether-cutting type and takes place in
the QSL. As the flux rope reaches the altitude at which the decay index - ln B/ ln z of the potential field exceeds
3/2, it rapidly accelerates upward, while the overlying arcade eventually develops an inverse tear-drop shape, as

  

Source: Aulanier, Guillaume - Observatoire de Paris

 

Collections: Physics