The dynamo bifurcation in rotating spherical shells

Vincent Morin^* and Emmanuel Dormy

MAG (CNRS/ENS/IPGP), Ecole Normale Supérieure, 24 rue Lhomond, 75252 Paris Cedex 05, France.

^*VM is now at: Laboratoire de Physique, Ecole Normale Supérieure de Lyon, CNRS UMR5672, 46 allée d'Italie, F-69364 Lyon, France.

International Journal of Modern Physics B, Volume: 23, Issues: 28-29(2009) pp. 5467-5482.

Abstract. We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions. We show that the nature of the bifurcation, which can be either supercritical or subcritical or even take the form of isola (or detached lobes) strongly depends on the parameters. This dependence is described in a range of parameters numerically accessible (which unfortunately remains remote from geophysical application), and we show how the magnetic Prandtl number and the Ekman number control these transitions.