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Steven R Cranmer Submitted: 2008-02-14 08:16
A theory for the heating of coronal magnetic flux ropes is developed.
The dissipated magnetic energy has two distinct contributions:
(1) energy injected into the corona as a result of granule-scale,
random footpoint motions, and (2) energy from the large-scale,
nonpotential magnetic field of the flux rope. The second type of
dissipation can be described in term of hyperdiffusion, a type of
magnetic diffusion in which the helicity of the mean magnetic field is
conserved. The associated heating rate depends on the gradient of the
torsion parameter of the mean magnetic field. A simple model of an
active region containing a coronal flux rope is constructed. We find
that the temperature and density on the axis of the flux rope are
lower than in the local surroundings, consistent with observations
of coronal cavities. The model requires that the magnetic field in
the flux rope is stochastic in nature, with a perpendicular length
scale of the magnetic fluctuations of order 1000 km.
Authors: A. A. van Ballegooijen and S. R. Cranmer
Projects: None
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Publication Status: ApJ, in press (v. 679, June 1, 2008), arXiv:0802.1751
Last Modified: 2008-02-14 09:53
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