Remarks on some typical assumptions in dynamo theory

TL;DR

This paper critically examines key assumptions in dynamo theory, discussing concepts like magnetic field generation, the Elsasser number, and the impact of eddy diffusivities, while exploring multiple dynamo states.

Contribution

It provides a critical analysis of common assumptions and introduces new insights into the coexistence of different dynamo states in spherical fluid shells.

Findings

Analogy between imposed and generated magnetic fields evaluated

Role of Elsasser number discussed

Effects of eddy diffusivities in simulations highlighted

Abstract

Some concepts used in the theory of convection-driven dynamos in rotating spherical fluid shells are discussed. The analogy between imposed magnetic fields and those generated by dynamo action is evaluated and the role of the Elsasser number is considered. Eddy diffusivities are essential ingredients in numerical dynamo simulations, but their effects could be misleading. New aspects of the simultaneous existence of different dynamo states are described.