AAS 204th Meeting, June 2004
Session 18 Coronal Mass Ejections
SPD Oral, Monday, May 31, 2004, 10:00-11:30am, 704

## [18.03] Numerical Simulations of 3D Coronal Magnetic Fields Resulting from the Emergence of Twisted Magnetic Flux Tubes

Y. Fan, S.E. Gibson (HAO/NCAR)

We present MHD simulations in the low-\beta regime of the evolution of the 3D coronal magnetic field as an arched, twisted magnetic flux tube is transported into a pre-existing coronal potential magnetic arcade. It is found that the line-tied emerging flux tube becomes kink unstable when a sufficient amount of twist is transported into the corona. For an emerging flux tube with a left-handed twist (which is the preferred sense of twist for active region flux tubes in the northern hemisphere), the kink motion of the tube and its interaction with the ambient coronal magnetic field lead to the formation of an intense current layer which displays an inverse-S shape, consistent with the X-ray sigmoid morphology preferentially seen in the northern hemisphere. Our simulation results may explain the X-ray sigmoid brightenings that are observed during eruptive flares and confirm the prediction by previous topological studies that magnetic tangential discontinuities (or current sheets) should form along the so called bald-patch'' separatrix surface, across which the connectivity of the coronal magnetic field with the dense photosphere undergoes a sharp transition. Finally, we will also present simulations in a 3D spherical geometry of a CME-like eruption of the coronal magnetic field due to the kink instability of a twisted magnetic flux rope emerging into the corona.