Solar surface and atmospheric dynamics: The Photosphere

TL;DR

This paper reviews solar magnetism, focusing on the quiet sun, and discusses the potential roles of small-scale and large-scale turbulent dynamos, highlighting current simulation limitations and observational evidence.

Contribution

It provides a detailed analysis of dynamo processes at different scales and compares observational data, emphasizing the challenges in linking simulations with solar magnetic phenomena.

Findings

Simulations are far from capturing solar magnetic complexity.

Internetwork fields are similar in Hinode and Hanle data.

Large voids suggest dynamo action may not occur in intergranular lanes.

Abstract

Various aspects of the magnetism of the quiet sun are reviewed. The suggestion that a small scale dynamo acting at granular scales generates what we call the quiet sun fields is studied in some detail. Although dynamo action has been proved numerically, it is argued that current simulations are still far from achieving the complexity that might be present on the Sun. We based this statement not so much on the low magnetic Reynolds numbers used in the simulations but, above all, in the smallness of the kinetic Reynolds numbers employed by them. It is argued that the low magnetic Prandtl number at the solar surface may pose unexpected problems for the identification of the observed internetwork fields with dynamo action at granular scales. Some form of turbulent dynamo at bigger (and deeper) scales is favored. The comparison between the internetwork fields observed by Hinode and the magnetism inferred from Hanle measurements are converging towards a similar description. They are both described as randomly oriented, largely transverse fields in the several hecto-Gauss range. These similarities are ever making more natural to assume that they are the same. However, and because of the large voids of magnetic flux observed in the spatial distribution of the internetwork fields, it is argued that they are not likely to be generated by dynamo action in the intergranular lanes. It is concluded that if a dynamo is acting at granular scales, the end product might have not been observed yet at current spatial resolutions and sensitivities with the Zeeman effect.