34th Solar Physics Division Meeting, June 2003
Session 1 Corona I
Oral, Monday, June 16, 2003, 9:00am-12:00noon, Auditorium

[1.03] Force-free Fields in Active Regions: Magnetic configurations and Energetics

S. Regnier, R. C. Canfield (Montana State University, Bozeman MT 59717, USA), T. Amari (Centre de Physique Theorique, Palaiseau 91128, France)

To determine the 3D configuration of solar active regions and to define boundary conditions for MHD codes, we reconstruct the coronal magnetic field from photospheric measurements. For that, we consider the active region in an equilibrium state. Three hypotheses are then often used: the potential field (no electric current), the linear force-free field (the current density is \alpha times the magnetic field, \alpha is a constant), the nonlinear force-free field (\alpha is a function of space). We here compare those three models in terms of connectivity changes and energetics for two different active regions: AR 8151 and AR 8210. AR 8151 shows dramatical changes between these models whereas AR 8210 configuration stays close to the potential field. The structure of the filament and of the sigmoid observed in AR 8151 can only be determined in the nonlinear force-free field: both structures are identified with twisted flux tubes with ~ 0.5-0.6 turns. Interestingly, the filament is a right-handed structure whereas the sigmoid is left-handed! This work is a part of the Solar MURI project.

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