Bootstrapping the coronal magnetic field with stereo: Unipolar potential field modeling

Abstract

We investigate the recently quantified misalignment of α mis ® 20°-40° between the three-dimensional geometry of stereoscopically triangulated coronal loops observed with STEREO/EUVI (in four active regions (ARs)) 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 the Michelson Doppler Imager. The forward-fitting method yields a best-fit magnetic field model with a reduced misalignment of αPF ≈ 13°-20°. We also evaluate stereoscopic measurement errors and find a contribution of αSE ≈ 7°-12°, which constrains the residual misalignment to αNP ≈ 11°-17°, which is likely due to the nonpotentiality of the ARs. The residual misalignment angle, αNP, of the potential field due to nonpotentiality is found to correlate with the soft X-ray flux of the AR, which implies a relationship between electric currents and plasma heating. © 2010. The American Astronomical Society. All rights reserved.