Are the Magnetic Fields Radial in the Solar Polar Region?

TL;DR

This study examines the orientation of photospheric magnetic fields in the solar polar region, revealing systematic deviations from radial alignment that depend on the assumed filling factor, suggesting potential resolution-related biases.

Contribution

It provides new insights into the magnetic field orientation in the solar polar region and highlights the impact of the filling factor on inferred magnetic inclinations.

Findings

Magnetic fields tend to tilt towards the pole in small polarization patches.

The inclination depends on the filling factor assumption, affecting the interpretation.

Limited resolution may introduce systematic biases in magnetic field measurements.

Abstract

We investigate the orientation of the photospheric magnetic fields in the solar polar region using observations from the Helioseismic and Magnetic Imager (HMI). Inside small patches of significant polarization, the inferred magnetic field vectors at $1''$ scale appear to systematically deviate from the radial direction. Most tilt towards the pole; all are more inclined toward the plane of sky compared to the radial vector. These results, however, depend on the "filling factor" $f$ that characterizes the unresolved magnetic structures. The default, uninformative $f\equiv1$ for HMI will incur larger inclination and less radial fields than $f<1$. The observed trend may be a systematic bias inherent to the limited resolution.