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The Astrophysical Journal, 718:13881399, 2010 August 1 doi:10.1088/0004-637X/718/2/1388 C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
 

Summary: The Astrophysical Journal, 718:1388­1399, 2010 August 1 doi:10.1088/0004-637X/718/2/1388
C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
CRITERIA FOR FLUX ROPE ERUPTION: NON-EQUILIBRIUM VERSUS TORUS INSTABILITY
P. D´emoulin and G. Aulanier
LESIA, Observatoire de Paris, CNRS, 5 place Jules Janssen, 92190 Meudon, France; Pascal.Demoulin@obspm.fr
Received 2010 April 7; accepted 2010 June 8; published 2010 July 15
ABSTRACT
The coronal magnetic configuration of an active region typically evolves quietly for a few days before becoming
suddenly eruptive and launching a coronal mass ejection (CME). The precise origin of the eruption is still under
debate. The loss of equilibrium, or an ideal magnetohydrodynamic (MHD) instability such as torus instability are
among the several mechanisms that have proposed to be responsible for the sudden eruptions. Distinct approaches
have also been formulated for limited cases having circular or translation symmetry. We revisit the previous theo-
retical approaches setting them in the same analytical framework. The coronal field results from the contribution of
a non-neutralized current channel added to a background magnetic field, which in our model is the potential field
generated by two photospheric flux concentrations. The evolution on short Alfv´enic timescale is governed by ideal
MHD. We first show analytically that the loss of equilibrium and the stability analysis are two different views of
the same physical mechanism. Second, we identify that the same physics is involved in the instabilities of circular
and straight current channels. Indeed, they are just two particular limiting cases of more general current paths. A
global instability of the magnetic configuration is present when the current channel is located at a coronal height,
h, large enough so that the decay index of the potential field, ln |Bp|/ ln h, is larger than a critical value. At

  

Source: Aulanier, Guillaume - Observatoire de Paris

 

Collections: Physics