Instrumental and Observational Artifacts in Quiet Sun Magnetic Flux Cance llation Functions

TL;DR

This study examines how observational artifacts like noise and network elements affect the measurement of quiet Sun magnetic flux using cancellation functions, highlighting the challenges in obtaining accurate estimates.

Contribution

The paper demonstrates that noise and network elements significantly bias the measurement of magnetic flux and cancellation exponents, providing upper bounds based on Hinode data.

Findings

Noise causes overestimation of flux and exponents.

Network elements lead to underestimated flux and exponents.

Current data cannot yield conclusive true flux values.

Abstract

Under the assumption that the photospheric quiet-Sun magnetic field is turbulent, the cancellation function has previously been used to estimate the true, resolution-independent mean, unsigned vertical flux $<|B_z|>_{\mathrm{true}}$. We show that the presence of network elements, noise, and seeing complicate the measurement of accurate cancellation functions and their power-law exponents $\kappa$. Failure to exclude network elements previously led to too low estimates of both the cancellation exponent $\kappa$ and of $<|B_z|>_{\mathrm{true}}$. However, both $\kappa$ and $<|B_z|>_{\mathrm{true}}$ are over-estimated due to noise in magnetograms. While no conclusive value can be derived with data from current instruments, our {\it Hinode}/SP results of $\kappa\lessapprox0.38$ and $<|B_z|>_{\mathrm{true}}\lessapprox 270 $gauss can be taken as upper bounds.