Reversals of a large scale field generated over a turbulent background

TL;DR

This paper investigates how large scale fields generated in turbulent systems can undergo spontaneous reversals, restoring symmetry statistically, across different physical contexts like dynamo magnetic fields, turbulent flows, and convection.

Contribution

It compares reversal mechanisms across diverse turbulent systems, highlighting the role of symmetries and their breaking in these phenomena.

Findings

Reversals occur in dynamo magnetic fields, large scale flows, and convection rolls.

Symmetries and their breaking influence the reversal mechanisms.

Different systems share common features in their reversal dynamics.

Abstract

We present a study of several systems in which a large scale field is generated over a turbulent background. These large scale fields usually break a symmetry of the forcing by selecting a direction. Under certain conditions, the large scale field displays reversals so that the symmetry of the forcing is recovered statistically. We present examples of such dynamics in the context of the dynamo instability, of two dimensional turbulent Kolmogorov flows and of turbulent Rayleigh-B\'enard convection. In these systems reversals occur respectively for the dynamo magnetic field, for the large scale circulation generated by a periodic forcing in space and for the large scale roll generated by turbulent thermal convection. We compare the mechanisms involved and show that their properties depend on some symmetries of the system and on the way they are broken.