HR: 1340h
AN: GP33A-0924    [Abstracts]
TI: Transitions in Dynamo Modes Controlled by the Domain Aspect Ratio
AU: * Goudard, L
EM: goudard@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Equipe MAG, Ecole Normale Supérieure, Département de Physique, LRA, 24 rue Lhomond, Paris, 75005, France
AU: Dormy, E
EM: dormy@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Equipe MAG, Ecole Normale Supérieure, Département de Physique, LRA, 24 rue Lhomond, Paris, 75005, France
AB: Magnetic fields of internal origin are observed on many planets in the solar system. The Sun itself acts as a dynamo. While these natural objects are very different in their composition, when it comes to dynamo modeling the governing equations are remarkably similar. One of the controlling parameters to distinguish between these objects is the aspect ratio of the convecting domain. Comparing the Sun to the Earth raises the issue of the nature of reversals. A challenging issue is to determine why the geomagnetic field reverses polarity on an irregular basis, whereas the Sun --which is a much larger object, governed by stronger nonlinearities-- reverses its magnetic polarity on a quasi-periodic timescale of 11 yrs. We use a three-dimensional Boussinesq model (the Parody code) to investigate the transition between these two types of behavior. We show that the aspect ratio of the convecting domain controls the nature of the dynamo field. We report a butterfly-like diagram at large aspect ratio, with magnetic activity near 30° of latitudes, which migrates with time toward the equator. We trace the existence of the dynamo wave solution at various aspect ratio and suggest possible consequences for the geomagnetic secular variation.
DE: 1510 Dynamo: theories and simulations
DE: 5734 Magnetic fields and magnetism
DE: 7524 Magnetic fields
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting