Strong large scale magnetic fields in rotating convection-driven dynamos: the important role of magnetic diffusion

TL;DR

This paper demonstrates through numerical simulations that strong large-scale magnetic fields in rotating convection-driven dynamos are possible when the flow remains rotationally constrained and magnetic diffusion plays a significant role at small scales.

Contribution

The study reveals that magnetic diffusion is crucial for sustaining large-scale magnetic fields in rotating convective dynamos, aligning with asymptotic predictions.

Findings

Large scale magnetic fields can be generated under specific conditions.

Rotational constraint of flow is essential for large scale dynamo action.

Magnetic diffusion at small scales is a key factor for large scale field growth.

Abstract

Natural dynamos such as planets and stars generate global scale magnetic field despite the inferred presence of small scale turbulence. Such systems are known as large scale dynamos and are typically driven by convection and influenced by rotation. Previous numerical studies of rotating dynamos generally find that the large scale magnetic field becomes weaker as the flow becomes more turbulent. The underlying physical processes necessary for sustaining so-called large scale dynamos is therefore still debated. Here we use a suite of numerical simulations to show that strong large scale magnetic fields can be generated in rotating convective turbulence provided that two conditions are satisfied: (1) the flow remains rotationally constrained; and (2) magnetic diffusion is important on the small convective length scale. These findings are in agreement with previous asymptotic predictions and suggest that natural dynamos might satisfy these two conditions.