Influence of the mass distribution on the magnetic field topology^⋆

¹ MAG (ENS/IPGP), LRA, Département de Physique, École normale supérieure, 24 rue Lhomond, 75252 Paris Cedex 5, France
e-mail: raphael.raynaud@ens.fr; ludovic@lra.ens.fr; dormy@phys.ens.fr
² LERMA, CNRS UMR 8112, 75005 Paris, France
³ IPGP, CNRS UMR 7154, 75005 Paris, France

Received: 28 March 2014
Accepted: 16 June 2014

Abstract

Context. Three-dimensional spherical dynamo simulations carried out within the framework of the anelastic approximation have revealed that the established distinction between dipolar and multipolar dynamos tends to be less clear than it was in Boussinesq studies. This result was first interpreted as a direct consequence of the existence of a larger number of models with a high equatorial dipole contribution, together with an intermediate dipole field strength. However, this finding has not been clearly related to specific changes that would have been introduced by the use of the anelastic approximation.

Aims. In this paper, we primarily focus on the effects of choosing a different mass distribution. Indeed, it is likely to have as large consequences as taking a stratified reference state into account would, especially when comparing our results to previous Boussinesq studies.

Methods. Our investigation is based on a systematic parameter study of weakly stratified anelastic dynamo models.

Results. We show that the tendencies highlighted in previous anelastic dynamo simulations are already present in the Boussinesq limit. Thus they cannot be systematically related to anelastic effects. Actually, a central mass distribution can result in changes in the magnetic field topology that are mainly due to the concentration of convective cells close to the inner sphere.