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Title:
A Parametric Study of Erupting Flux Rope Rotation. Modeling the "Cartwheel CME" on 9 April 2008
Authors:
Kliem, B.; Török, T.; Thompson, W. T.
Affiliation:
AA(Insitut für Physik und Astronomie, Universität Potsdam; Mullard Space Science Laboratory, University College London), AB(LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot; , Predictive Science, Inc.), AC(Adnet Systems Inc., NASA Goddard Space Flight Center)
Publication:
Solar Physics, Volume 281, Issue 1, pp.137-166 (SoPh Homepage)
Publication Date:
11/2012
Origin:
SPRINGER
Keywords:
Corona, active, Prominences, dynamics, Coronal mass ejections, initiation and propagation, Magnetic fields, corona, Magnetohydrodynamics
Abstract Copyright:
(c) 2012: Springer Science+Business Media B.V.
DOI:
10.1007/s11207-012-9990-z
Bibliographic Code:
2012SoPh..281..137K

Abstract

The rotation of erupting filaments in the solar corona is addressed through a parametric simulation study of unstable, rotating flux ropes in bipolar force-free initial equilibrium. The Lorentz force due to the external shear-field component and the relaxation of tension in the twisted field are the major contributors to the rotation in this model, while reconnection with the ambient field is of minor importance, due to the field's simple structure. In the low-beta corona, the rotation is not guided by the changing orientation of the vertical field component's polarity inversion line with height. The model yields strong initial rotations which saturate in the corona and differ qualitatively from the profile of rotation vs. height obtained in a recent simulation of an eruption without preexisting flux rope. Both major mechanisms writhe the flux rope axis, converting part of the initial twist helicity, and produce rotation profiles which, to a large part, are very similar within a range of shear-twist combinations. A difference lies in the tendency of twist-driven rotation to saturate at lower heights than shear-driven rotation. For parameters characteristic of the source regions of erupting filaments and coronal mass ejections, the shear field is found to be the dominant origin of rotations in the corona and to be required if the rotation reaches angles of order 90 degrees and higher; it dominates even if the twist exceeds the threshold of the helical kink instability. The contributions by shear and twist to the total rotation can be disentangled in the analysis of observations if the rotation and rise profiles are simultaneously compared with model calculations. The resulting twist estimate allows one to judge whether the helical kink instability occurred. This is demonstrated for the erupting prominence in the "Cartwheel CME" on 9 April 2008, which has shown a rotation of ≈ 115o up to a height of 1.5 R &sun; above the photosphere. Out of a range of initial equilibria which include strongly kink-unstable (twist Phi=5 pi), weakly kink-unstable (Phi=3.5 pi), and kink-stable (Phi=2.5 pi) configurations, only the evolution of the weakly kink-unstable flux rope matches the observations in their entirety.
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