Probing quiet Sun magnetism using MURaM simulations and Hinode/SP results: support for a local dynamo

TL;DR

This study combines MURaM simulations and Hinode/SP observations to investigate quiet Sun magnetism, supporting the hypothesis that a local surface dynamo significantly contributes to the magnetic flux observed in internetwork regions.

Contribution

It demonstrates that surface dynamo simulations at high magnetic Reynolds numbers can reproduce observed magnetic flux ratios, suggesting a dominant role of local dynamo action in quiet Sun magnetism.

Findings

Simulations with mixed-polarity fields match observed vertical flux density.

Surface dynamo at high Rm produces horizontal/vertical flux ratios consistent with observations.

Scaling the magnetic field by a factor of 2-3 aligns simulations with observed internetwork magnetic signals.

Abstract

We obtain information about the magnetic flux present in the quiet Sun by comparing radiative MHD simulations with Hinode/SP observations, with particular emphasis on the role of surface dynamo action. Simulation runs with different magnetic Reynolds numbers (Rm) are used together with observations at different heliocentric angles with different levels of noise. The results show that simulations with an imposed mixed-polarity field and Rm below the threshold for dynamo action reproduce the observed vertical flux density, but do not display a sufficiently high horizontal flux density. Surface dynamo simulations at the highest Rm feasible at the moment yield a ratio of the horizontal and vertical flux density consistent with observational results, but the overall amplitudes are too low. Based on the properties of the local dynamo simulations, a tentative scaling of the magnetic field strength by a factor 2 - 3 reproduces the signal observed in the internetwork regions. We find an agreement with observations at different heliocentric angles. The mean field strength in internetwork, implied by our analysis, is roughly 170 G at the optical depth unity. Our study shows that surface dynamo could be responsible for most of the magnetic flux in the quiet Sun outside the network given that the extrapolation to higher Rm is valid.