Subharmonic Dynamo Action of Fluid Motions with Two-Dimensional Periodicity

Kinematic dynamos based on steady velocity fields with two-dimensional periodicity are analysed numerically. The velocity fields of the study by G. O. Roberts (1972) are used and the analysis is extended to the case when the spatial periodicity of the magnetic field differs from that of the velocity field not only in the homogeneous third direction. While the solutions of Roberts correspond to the most efficient dynamos in most cases, there are some cases in which spatially subharmonic dynamos are preferred.