Asymptotic methods in the nonlinear mean-field dynamo

Abstract

We discuss the methods and results of analysis of nonlinear mean-field dynamo models based on a-quenching in two asymptotic regimes, namely for weakly and highly supercritical excitation. In the former case the spatial distribution of the steady-state magnetic field is close to that given by the neutrally stable eigenfunction of the corresponding kinematic dynamo. In the latter case the magnetic field distribution within the main part of the dynamo volume is presumably determined by the balance between the Lorentz and Coriolis forces while near the boundaries boundary layers arise in which the field adjusts itself to the boundary conditions. The asymptotic behaviour of the highly supercritical aw-dynamos is sensitive to the particular form of dependence of the mean helicity on magnetic field while α²-dynamos are less sensitive to this dependence.