Horizontal or vertical magnetic fields on the quiet Sun: Angular distributions and their height variations

TL;DR

This study uses a novel polarization analysis method to determine the height-dependent angular distribution of quiet Sun magnetic fields, resolving previous contradictions about their orientation.

Contribution

It introduces a new approach based on symmetry properties of the transverse Zeeman effect that avoids polarization combination issues and systematic errors.

Findings

Magnetic fields are vertical in the lower photosphere.

Magnetic fields become horizontal in the upper photosphere.

Method provides model- and resolution-independent results.

Abstract

Different analyses of identical Hinode SOT/SP data of quiet-sun magnetic fields have in the past led to contradictory answers to the question of whether the angular distribution of field vectors is preferentially horizontal or vertical. These answers have been obtained by combining the measured circular and linear polarizations in different ways to derive the field inclinations. A problem with these combinations is that the circular and linear polarizations scale with field strength in profoundly different ways. Here, we avoid these problems by using an entirely different approach that is based exclusively on the fundamental symmetry properties of the transverse Zeeman effect for observations away from the disk center without any dependence on the circular polarization. Systematic errors are suppressed by the application of a doubly differential technique with the 5247-5250 \AA\ line pair for observations with the ZIMPOL-2 imaging polarimeter on the French THEMIS telescope on Tenerife. This allows us to determine in a model- and resolution-independent way how the angular distribution of the intranetwork magnetic fields changes from being preferentially vertical in the lower and middle photosphere to become preferentially horizontal in the upper photosphere.