HR: 10:20h
AN: SH21C-01 INVITED     [PDF]
TI: Magnetic Configuration in Low Solar Atmosphere Prior to Eruptions
AU: * van Ballegooijen, A A
EM: vanballe@cfa.harvard.edu
AF: Harvard-Smithsonian Center for Astrophysics, MS 15 60 Garden Street, Cambridge, MA 02138 United States
AB: Vector magnetograph observations of active regions prior to large flares often show strongly sheared magnetic fields, and the associated H$\alpha$ filaments show long threads parallel to the neutral line. This suggests that the filament is embedded in a horizontal flux tube that is basically untwisted. In contrast, eruptive prominences often show helical structures, suggesting a flux rope with multiple twists. To reconcile these observations, we propose a model of the pre-eruptive state in which an untwisted horizontal flux tube is held down by an overlying magnetic arcade. Unlike in previous models, electric currents flow mainly at the interface between the two flux systems. The two ends of the flux tube are anchored in the photosphere. We use 3D MHD modeling based on NSO/KP magnetograph data to demonstrate that such a system can be in stable force-free equilibrium, provided the arcade field is sufficiently strong to restrain the flux tube. A weakening of the arcade or interaction with a neighboring filament can cause loss of magnetostatic equilibrium, resulting in the eruption of part of the flux tube (Sturrock et al. 2001, ApJ 548, 492). Magnetic reconnection during the early phase of the eruption causes the arcade field to be wrapped around the filament flux, creating the unstable flux rope seen in erupting prominences. The model is applied to H$\alpha$ observations of a filament obtained at the Swedish Vacuum Solar Telescope (La Palma) and TRACE observation of its eruption on June 21-22, 1998.
DE: 7513 Coronal mass ejections
DE: 7519 Flares
DE: 7524 Magnetic fields
DE: 7531 Prominence eruptions
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting