34th Solar Physics Division Meeting, June 2003
Session 23 Coronal Mass Ejections II
Oral, Thursday, June 19, 2003, 11:00am-12:00noon, Auditorium

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[23.04] Acceleration of Coronal Mass Ejections

J. Chen, J. Krall (Plasma Physics Division, NRL)

The acceleration of coronal mass ejections (CMEs) is examined focusing on two specific questions raised by observations: (1) what determines the height beyond which a CME exhibits no rapid acceleration and (2) why is the main acceleration of CMEs typically limited to below 2--3 solar radii. Using a theoretical model of CMEs based on a three-dimensional (3-D) magnetic flux rope, it is shown that acceleration of all flux-rope CMEs exhibits a critical height Z* = Sf/2 above which the acceleration monotonically decreases in magnitude, where Sf is the fixed footpoint separation distance. Thus, scaled to the distance Sf, the acceleration-height curves have a universal scaling law for flux-rope CMEs. Theoretical analysis and observed CME dynamics show two distinct phases of acceleration according to the apex height---the main (Z \le 2 Sf) and residual (Z \ge 2 Sf) acceleration phases. This provides a physical explanation of so-called ``impulsive'' and ``gradual'' acceleration. The results also imply that the observed main acceleration phase can be used to infer Sf. The universal scaling is traced to the 3-D geometry of the flux rope underlying a CME, its inductive properties, and the Lorentz self-force. The theory is quantitatively tested against a number of observed CME events. \bigskip 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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