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R. Wolfson (Middlebury College)
Coronal mass ejections (CMEs) have been called ``the most energetic events in the solar system." In one widely accepted scenario, the energy that drives mass ejections accumulates slowly in the corona over a period of some days before the eruptive outburst that marks the start of the mass ejection. That accumulated energy must be sufficient not only to accelerate the ejected mass and to lift it against solar gravity, but it must also open the coronal magnetic field to allow the plasma egress to interplanetary space. The well-known Aly-Sturrock theorem shows that it is impossible to store sufficient energy in a simple force-free magnetic arcade, since the upper bound for such force-free energy is that of the fully open field only. We have shown in earlier work that additional energy, sufficient to lift and accelerate the ejecta, can be obtained from non-force-free currents. This assumes that force-free currents are responsible for enough energy to open the field. However, the Aly-Sturrock theorem only sets an upper bound; it does not guarantee the existence simple force-free states whose energy approaches that bound. In the present work, we explore force-free equilibria of simple magnetic arcades, and show that it may not always be possible to store sufficient energy to open the field without topological changes such as the formation of current sheets or detached flux ropes. Just how much energy can be stored appears to depend on details of the magnetic flux distribution at the coronal base, and on the shear profile applied to the base field. Our results also suggest that force-free fields including detached flux ropes may exceed the Aly-Sturrock energy limit.
The author(s) of this abstract have provided an email address for comments about the abstract: wolfson@middlebury.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.