Blowout bifurcations and the onset of magnetic dynamo action

This paper numerically investigates the magnetohydrodynamic equations in th ree dimensions with periodic boundary conditions in a parameter range where a forced fluid flow is chaotic. It is found that the transition to dynamo action, whereby the magnetic field is sustained by interaction with the for ced flow, is a blowout bifurcation. The blowout bifurcation is typified by bursting behavior, or "on-off intermittency." In particular, near the trans ition there are short, intermittently occurring bursts of strong magnetic f ield activity where the total magnetic energy is comparable to the total fl ow kinetic energy. Between these bursts the magnetic energy is very small. As one approaches the transition from the dynamo-active side, the time betw een bursts becomes longer and longer, approaching infinity at the transitio n. Numerical verification is given for the presence of signature scaling la ws in numerical computations utilizing a pseudospectral model with triply p eriodic boundary conditions. This work implies specific testable prediction s for experimental dynamos. (C) 2001 American Institute of Physics.