[Previous] | [Session 2] | [Next]
P.A. Sturrock (Stanford University), M.E. Wheatland (University of Sydney), R. Wolfson (Middlebury College)
One of the current models for explaining coronal mass ejections (CMEs) comprises a twisted flux tube, anchored at each end in the photosphere and confined by an overlying magnetic arcade. It is known that the flux tube becomes MHD unstable if it is twisted sufficiently. However, linear theory does not tell us what would be the result of such an instability. An onset of instability can be either explosive or non-explosive. In the present context, the former could lead to the eruption of part of the flux tube into interplanetary space, i.e. to a CME. On the other hand, the latter would lead only to a slow re-structuring of the magnetic configuration with no dramatic effects.
We can gain some insight into this distinction by considering the energy required to produce the kind of eruption that could explain a CME. We make a simple estimate of this requirement by comparing the energy before and after an eruption. The former is essentially the free energy of a twisted flux tube of given length - the excess of the energy of the twisted flux tube over the energy of the corresponding untwisted flux tube. The latter comprises the energy of that part of the flux tube which extends into interplanetary space, together with the energy which is required to create an opening in the arcade sufficiently large to permit the penetration of the flux tube.
This work was supported in part by NASA grants NAS 8-37334 and NAG 5-4038.