The Solar Coronal Magnetic Field Measurements With SOLARC

TL;DR

This paper discusses the use of the SOLARC instrument for direct measurements of the solar coronal magnetic field using infrared polarimetry, highlighting initial comparisons with potential field models and addressing challenges in magnetic field reconstruction.

Contribution

It presents the first observational results of coronal magnetic fields with SOLARC and analyzes the limitations and challenges in reconstructing real coronal magnetic structures.

Findings

Potential field models approximate observed coronal fields above stable sunspots.

Infrared polarimetric measurements can detect weak coronal magnetic fields.

Challenges include Van Vleck effect and inversion problems in magnetic field reconstruction.

Abstract

Direct solar coronal magnetic field measurements have become possible since recent development of high-sensitivity infrared detection technology. The SOLARC instrument installed on Mt. Haleakala is such a polarimetric coronagraph that was designed for routinely observing Stokes parameter profiles in near infrared (NIR) wavelengthes. The Fe$^{+12}$ 1075 nm forbidden coronal emission line (CEL) is potential for weak coronal magnetic field detection. As a first step the potential field model has been used to compare with the SOLARC observation in the Fe$^{+12}$ 1075 nm line (Liu and Lin 2008). It's found that the potential fields can be a zeroth-order proxy for approaching the observed coronal field above a simple stable sunspot. In this paper we further discuss several nodi that are hampering the progress for reconstructing the real coronal magnetic field structures. They include the well-known Van Vleck effect in linear polarization signals, ignorance of the information of the NIR emission sources (i.e., inversion problem of coronal magnetic fields), a fat lot of global non-linear force-free field tools available for better modeling coronal magnetic fields, and so on.