On the Generation of Equipartition-Strength Magnetic Fields by Turbulent Hydromagnetic Dynamos

Abstract

The generation of a mean magnetic field by the action of small-scale turbulent fluid motions, the α-effect, is a fundamental ingredient of mean-field dynamo theory. However, recent mathematical models and numerical experiments are providing increasingly strong support to the notion that at high magnetic Reynolds numbers, the α-effect is strongly impeded long before the mean magnetic field has reached energy equipartition with the driving fluid motions. Taken at face value, this raises serious doubt as to whether the solar magnetic field is produced by a turbulent hydromagnetic dynamo after all, since it is an observed fact that the Sun does possess a structured, large-scale mean magnetic field of strength comparable to equipartition. In this Letter we demonstrate that the class of mean-field turbulent hydromagnetic models known as interface dynamos can produce equipartition-strength mean magnetic fields even in the presence of strong α-quenching.