Azimuth ambiguity removal and non-linear force-free extrapolation of near-limb magnetic regions

TL;DR

This paper presents a method combining azimuth ambiguity removal and non-linear force-free extrapolation for near-limb magnetic regions, enabling accurate magnetic field analysis regardless of solar disk position.

Contribution

It introduces a spherical geometry-adapted Metropolis algorithm for azimuth ambiguity resolution and applies an optimization-based extrapolation method to boundary magnetograms.

Findings

Exact correspondence between estimated fields and nonpotential loop structures.

Effective ambiguity removal independent of solar disk position.

Successful magnetic field extrapolation in nonlinear force-free approximation.

Abstract

Possibilities in principle for satisfactory removal of the 180-azimuthal ambiguity in the transverse field of vector magnetograms and the extrapolation of magnetic fields independently of their position on the solar disk are shown. Revealed here is an exact correspondence between the estimated field and the nonpotential loop structure on the limb. The Metropolis's algorithm modified to work in spherical geometry is used to resolve the azimuthal ambiguity. Based on a version of the optimization method from Rudenko and Myshyakov (2009), we use corrected magnetograms as boundary conditions for magnetic field extrapolation in the nonlinear force-free approximation.