Coronal Magnetic Fields Derived with Images Acquired during the 2017 August 21 Total Solar Eclipse

Abstract

The coronal magnetic field, despite its overwhelming importance to the physics and dynamics of the corona, has only rarely been measured. Here, electron density maps derived from images acquired during the total solar eclipse of 2017 August 21 are employed to demonstrate a new technique to measure 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 very good agreement. Other parameters such as the plasma β and Alfvén 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 filtered images, also finding 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 coronal magnetic field strengths and inclinations projected on the POS. These are among the main missing pieces of information that have limited so far our understanding of physical phenomena going on in the solar corona.

Refinement of Global Coronal and Interplanetary Magnetic Field Extrapolations Constrained by Remote-sensing and In Situ Observations at the Solar Minimum

“…Quantifying the splitting of spectral lines caused by the Zeeman effect is an essential method to measure the magnetic fields. Although direct measurements of weak CMFs are challenging, some new diagnostic techniques have been developed (Chen et al 2020;Yang et al 2020;Wei et al 2021;Landi et al 2022;Tan 2022;Trujillo Bueno & del Pino Alemán 2022;Bemporad 2023;Chen et al 2023). The IMFs can be indirectly measured through the detection of the cosmic-ray Sun shadow, as demonstrated by the Tibet AS-γ (Amenomori et al 2013(Amenomori et al , 2018, IceCube (Aartsen et al 2017(Aartsen et al , 2021, and Large High Altitude Air Shower Observatory (LHAASO; Cao et al 2019;Jia et al 2022;Nan et al 2022;Li et al 2023) experiments.…”