34th Solar Physics Division Meeting, June 2003
Session 4 Corona II
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[4.16] The Emergence of a Twisted Magnetic Flux Tube into a Pre-existing Coronal Arcade

Y. Fan, S. E. Gibson (HAO, National Center for Atmospheric Research)

To investigate the dynamic evolution of coronal magnetic field in response to the emergence of significantly twisted magnetic structures, we perform MHD simulations in the low-\beta regime of the emergence of a twisted magnetic flux tube into a pre-existing coronal potential magnetic arcade. Our simulation of a twisted flux tube, which when fully emerged, contains a twist of 1.875 \times 2 \pi field-line rotation about the axis between the anchored footpoints, leads to a magnetic structure with substantial writhing of the tube axis (apex rotation > 90\circ) as a result of the non-linear evolution of the kink instability. For an emerging tube with a left-handed twist (which is the preferred sense of twist for active regions in the northern hemisphere), the writhing of the tube is also left-handed, producing a forward S-shape for the tube axis as viewed from the top, which is opposite to the inverse S-shaped X-ray sigmoid structures preferentially seen in the northern hemisphere. However we find that the writhing motion of the tube and its interaction with the ambient coronal magnetic field also drives the formation of an intense current layer which displays an inverse S-shape, consistent with the shape of X-ray sigmoids. We compare the resulting current layer from the dynamic simulation with an analysis of the separatrix surface between winding and non-winding fields at various states of emergence.

The National Center for Atmospheric Research is sponsored by the National Science Foundation. This work is supported in part by AFOSR grant F49620-02-0191.


The author(s) of this abstract have provided an email address for comments about the abstract: yfan@hao.ucar.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.