Non-linear and chaotic dynamo regimes

TL;DR

This paper reviews current understanding and open questions in solar and stellar dynamo theories, highlighting recent progress in modeling magnetic activity, the role of magnetic helicity fluxes, and the comparison of simulations with observations.

Contribution

It provides an update on dynamo regimes, discusses the significance of magnetic helicity fluxes, and emphasizes the importance of nonlocal modeling in stellar dynamo research.

Findings

Numerical simulations now reproduce solar-like equatorward migration.

Uncertainty remains about the relationship between stellar cycle frequencies and rotation.

The role of magnetic helicity fluxes in dynamo processes is increasingly recognized.

Abstract

An update is given on the current status of solar and stellar dynamos. At present, it is still unclear why stellar cycle frequencies increase with rotation frequency in such a way that their ratio increases with stellar activity. The small-scale dynamo is expected to operate in spite of a small value of the magnetic Prandtl number in stars. Whether or not the global magnetic activity in stars is a shallow or deeply rooted phenomenon is another open question. Progress in demonstrating the presence and importance of magnetic helicity fluxes in dynamos is briefly reviewed, and finally the role of nonlocality is emphasized in modeling stellar dynamos using the mean-field approach. On the other hand, direct numerical simulations have now come to the point where the models show solar-like equatorward migration that can be compared with observations and that need to be understood theoretically.