Coronal Magnetic Fields derived with Images acquired during the 21 August 2017 Total Solar Eclipse

TL;DR

This paper introduces a novel technique to measure coronal magnetic fields using electron density maps from total solar eclipse images, achieving good agreement with advanced MHD models and providing key missing information about the solar corona.

Contribution

The study demonstrates for the first time that 2D electron density distributions from eclipse images can reliably determine coronal magnetic field strengths and orientations.

Findings

Coronal magnetic field strengths derived from eclipse images match MHD simulation results.

Plasma-$eta$ and Alfvén velocity parameters are consistent with models.

POS magnetic field orientations closely agree with reconstructions.

Abstract

The coronal magnetic field, despite its overwhelming importance to the physics and dynamics of the corona, has only rarely been measured. Here, the electron density maps derived from images acquired during the total solar eclipse of August 21st, 2017 are employed to demonstrate a new technique to measure the coronal magnetic fields. The strength of the coronal magnetic fields is derived with a semiempirical formula relating the plasma magnetic energy density to the gravitational potential energy. The resulting values are compared with those provided by more advanced coronal field reconstruction methods based on MHD simulations of the whole corona starting from photospheric field measurements, finding a very good agreement. Other parameters such as the plasma-$\beta$ and Alfv\'en velocity are also derived and compared with those of MHD simulations. Moreover, the plane-of-sky (POS) orientation of the coronal magnetic fields is derived from the observed inclination of the coronal features in the filtered images, also finding a close agreement with magnetic field reconstructions. Hence, this work demonstrates for the first time that the 2D distribution of coronal electron densities measured during total solar eclipses is sufficient to provide the coronal magnetic field strengths and inclinations projected on the POS. These are among the main missing pieces of information that limited so far our understanding of physical phenomena going on in the solar corona.