Realistic modeling of local dynamo processes on the Sun

TL;DR

This paper demonstrates through 3D radiative MHD simulations that small-scale magnetic fields on the Sun result from a local dynamo process in the shallow convection zone, explaining observed magnetic patterns and structures.

Contribution

It provides the first detailed simulation-based evidence that local dynamo action in the Sun's shallow layers generates observed small-scale magnetic fields and loops.

Findings

Magnetic fields can grow from extremely weak seed fields to over 2000 G.

Local dynamo operates mainly in a 500 km deep subsurface layer.

Generated magnetic loops explain observed magnetic field orientations.

Abstract

Magnetic fields are usually observed in the quiet Sun as small-scale elements that cover the entire solar surface (the `salt and pepper' patterns in line-of-sight magnetograms). By using 3D radiative MHD numerical simulations we find that these fields result from a local dynamo action in the top layers of the convection zone, where extremely weak 'seed' magnetic fields (e.g., from a $10^{-6}$ G) can locally grow above the mean equipartition field, to a stronger than 2000~G field localized in magnetic structures. Our results reveal that the magnetic flux is predominantly generated in regions of small-scale helical downflows. We find that the local dynamo action takes place mostly in a shallow, about 500~km deep, subsurface layer, from which the generated field is transported into the deeper layers by convective downdrafts. We demonstrate that the observed dominance of vertical magnetic fields at the photosphere and horizontal fields above the photosphere can be explained by small-scale magnetic loops produced by the dynamo. Such small-scale loops play an important role in the structure and dynamics of the solar atmosphere and that their detection in observations is critical for understanding the local dynamo action on the Sun.