Bootstrapping the Coronal Magnetic Field with STEREO: I. Unipolar Potential Field Modeling

Abstract

We investigate the recently quantified misalignment of ${\alpha }_{mis}\approx 20^{\circ }-40^{\circ }$ between the 3-D geometry of stereoscopically triangulated coronal loops observed with STEREO/EUVI (in four active regions) and theoretical (potential or nonlinear force-free) magnetic field models extrapolated from photospheric magnetograms. We develop an efficient method of bootstrapping the coronal magnetic field by forward-fitting a parameterized potential field model to the STEREO-observed loops. The potential field model consists of a number of unipolar magnetic charges that are parameterized by decomposing a photospheric magnetogram from MDI. The forward-fitting method yields a best-fit magnetic field model with a reduced misalignment of ${\alpha }_{PF}\approx 13^{\circ }-20^{\circ }$. We evaluate also stereoscopic measurement errors and find a contribution of ${\alpha }_{SE}\approx 7^{\circ }-12^{\circ }$, which constrains the residual misalignment to ${\alpha }_{NP}={\alpha }_{PF}-{\alpha }_{SE}\approx 5^{\circ }-9^{\circ }$, which is likely due to the nonpotentiality of the active regions. The residual misalignment angle ${\alpha }_{NP}$ of the potential field due to nonpotentiality is found to correlate with the soft X-ray flux of the active region, which implies a relationship between electric currents and plasma heating.

12 figures, manuscript submitted to ApJ, 2010 Apr 27

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