Mapping Solar Magnetic Fields from the Photosphere to the Base of the Corona

TL;DR

This study provides detailed spectropolarimetric mapping of the Sun's magnetic field from the photosphere to the upper chromosphere, revealing how magnetic coupling drives heating in active regions.

Contribution

It presents the first comprehensive magnetic field measurements across multiple solar atmospheric layers using ultraviolet and visible spectropolarimetry.

Findings

Magnetic field strengths exceed 300 gauss at the upper chromosphere.

Magnetic fields are strongly correlated with Mg II k line intensity.

The magnetic coupling explains the heating in the plage chromosphere.

Abstract

Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet we remain blind to its main driver, the magnetic field. Here we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg II $h$ & $k$ and Mn I) and visible (Fe I) lines. We infer the longitudinal magnetic field from the photosphere to the very upper chromosphere. At the top of the plage chromosphere the field strengths reach more than 300 gauss, strongly correlated with the Mg II $k$ line core intensity and the electron pressure. This unique mapping shows how the magnetic field couples the different atmospheric layers and reveals the magnetic origin of the heating in the plage chromosphere.