Modelling and Interpreting The Effects of Spatial Resolution on Solar Magnetic Field Maps

TL;DR

This study compares methods for simulating the impact of spatial resolution on solar magnetic field maps, revealing how different approaches affect the interpretation of magnetic structures and guiding future inter-instrument comparisons.

Contribution

It introduces and evaluates four methods for modeling spatial resolution effects on magnetic field maps, highlighting their strengths and limitations for accurate solar magnetic field analysis.

Findings

Areas with high magnetic fill fractions are less affected by resolution degradation.

Worsening resolution tends to increase average field strength and decrease total flux.

Unresolved maps do not accurately represent the true distribution of magnetic fields.

Abstract

Different methods for simulating the effects of spatial resolution on magnetic field maps are compared, including those commonly used for inter-instrument comparisons. The investigation first uses synthetic data, and the results are confirmed with {\it Hinode}/SpectroPolarimeter data. Four methods are examined, one which manipulates the Stokes spectra to simulate spatial-resolution degradation, and three "post-facto" methods where the magnetic field maps are manipulated directly. Throughout, statistical comparisons of the degraded maps with the originals serve to quantify the outcomes. Overall, we find that areas with inferred magnetic fill fractions close to unity may be insensitive to optical spatial resolution; areas of sub-unity fill fractions are very sensitive. Trends with worsening spatial resolution can include increased average field strength, lower total flux, and a field vector oriented closer to the line of sight. Further-derived quantities such as vertical current density show variations even in areas of high average magnetic fill-fraction. In short, unresolved maps fail to represent the distribution of the underlying unresolved fields, and the "post-facto" methods generally do not reproduce the effects of a smaller telescope aperture. It is argued that selecting a method in order to reconcile disparate spatial resolution effects should depend on the goal, as one method may better preserve the field distribution, while another can reproduce spatial resolution degradation. The results presented should help direct future inter-instrument comparisons.