From convective to stellar dynamos

TL;DR

This paper reviews convective dynamos driven by rotation, emphasizing the role of the alpha effect in generating large-scale magnetic fields, and discusses implications for solar and stellar magnetic phenomena.

Contribution

It demonstrates that convective dynamos can be explained by an alpha effect and provides simulation evidence for turbulent alpha^2 dynamos without shear.

Findings

Large-scale magnetic fields saturate on resistive timescales.

Simulations support the existence of alpha^2 dynamos.

Implications for solar and stellar magnetic fields are discussed.

Abstract

Convectively driven dynamos with rotation generating magnetic fields on scales large compared with the scale of the turbulent eddies are being reviewed. It is argued that such fields can be understood as the result of an alpha effect. Simulations in Cartesian domains show that such large-scale magnetic fields saturate on a time scale compatible with the resistive one, suggesting that the magnitude of the alpha effect is here still constrained by approximate magnetic helicity conservation. It is argued that, in the absence of shear and/or any other known large-scale dynamo effects, these simulations prove the existence of turbulent alpha^2-type dynamos. Finally, recent results are discussed in the context of solar and stellar dynamos.