Mechanism of local dynamo action on the Sun

TL;DR

This paper uses 3D radiative MHD simulations to show that small-scale magnetic elements on the Sun are generated by a local dynamo in the shallow convection zone, explaining observed magnetic field orientations.

Contribution

It demonstrates the operation of a local dynamo in the Sun's shallow convection zone and explains magnetic field observations through multi-scale magnetic loops.

Findings

Local dynamo operates in a ~500 km deep layer.

Seed magnetic fields can grow from 10^{-6} G to over 1000 G.

Vertical and horizontal magnetic field patterns are explained by dynamo-produced loops.

Abstract

In the quiet Sun, magnetic fields are usually observed as small-scale magnetic elements, `salt and pepper', covering the entire solar surface. By using 3D radiative MHD numerical simulations we demonstrate that these fields are a result of local dynamo action in the top layers of the convection zone, where extremely weak `seed' magnetic fields can locally grow above the mean equipartition field (e.g., from a $10^{-6}$ G `seed' field to more than 1000 G magnetic structures). We find that the local dynamo action takes place only in a shallow, about 500 km deep, subsurface layer, from which the generated field is transported into deeper layers by convection downdrafts. We demonstrate that the observed dominance of vertical magnetic fields at the photosphere and the horizontal fields above the photosphere can be explained by multi-scale magnetic loops produced by the dynamo.