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J. Chen, J. Krall (NRL)
We examine the initial acceleration of CMEs using LASCO C1 and C2 data. Assuming that the underlying magnetic geometry is that of a flux rope and using the lengths of observed magnetic neutral lines or filament channels as proxies for the separation distance Sf between the two footpoints of a flux rope, it is shown that the peak acceleration occurs at height Z above the critical height Z* = Sf/2. Furthermore, the bulk of the acceleration subsides at height approximately equal to 3 Z*. These observed properties are in agreement with a theoretical prediction based on a model of erupting flux ropes [1]. The results imply that the observed height at which acceleration reaches maximum scales with Sf so that the more compact a flux rope is, the lower the height where the main acceleration ends. Above this height, a CME exhibits at most weak acceleration relative to the main acceleration. We have analyzed several CMEs for which the initial acceleration and the source region can be identified and have found the scaling law to be valid. This scaling law is universal in that it depends only on the pre-eruptive flux-rope geometry and can serve as a characteristic indicator of flux ropes.
1. Chen, J., and J. Krall, JGR, 108 (A11), 1410, doi:10.1029/2003JA009849, 2003.
Work supported by ONR and NASA
The author(s) of this abstract have provided an email address for comments about the abstract: chen@ppd.nrl.navy.mil
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Bulletin of the American Astronomical Society, 36 #2
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