Measurement of the evolution of the magnetic field of the quiet photosphere during a solar cycle

TL;DR

This study investigates how the magnetic flux in the quiet solar photosphere evolves over a solar cycle by using the Hanle effect to measure tangled magnetic fields on small scales.

Contribution

It introduces a synoptic observational program employing the differential Hanle effect to monitor magnetic flux variations over nearly one solar cycle.

Findings

Magnetic flux in the quiet photosphere varies with the solar cycle.

The Hanle effect effectively probes small-scale magnetic fields.

Results span almost a complete solar cycle.

Abstract

The solar photosphere is filled by a magnetic field which is tangled on scales much smaller than the resolution capability of solar telescopes. This hidden magnetic field can be investigated via the Hanle effect. In 2007 we started a synoptic program to explore if the magnetic flux of the quiet photosphere varies with the solar cycle. For this purpose we applied a differential Hanle effect technique based on observations of scattering polarization in C$_2$ molecular lines around 514.0 nm, taken generally every month. Our results now span almost one complete solar cycle.