title: Gyre-driven decay of the Earth's magnetic dipole.
abstract: Direct observations indicate that the magnitude of the Earth's magnetic axial dipole has decreased over the past 175 years; it is now 9% weaker than it was in 1840. Here we show how the rate of dipole decay may be controlled by a planetary-scale gyre in the liquid metal outer core. The gyre's meridional limbs on average transport normal polarity magnetic flux equatorward and reverse polarity flux poleward. Asymmetry in the geomagnetic field, due to the South Atlantic Anomaly, is essential to the proposed mechanism. We find that meridional flux advection accounts for the majority of the dipole decay since 1840, especially during times of rapid decline, with magnetic diffusion making an almost steady contribution generally of smaller magnitude. Based on the morphology of the present field, and the persistent nature of the gyre, the current episode of dipole decay looks set to continue, at least for the next few decades.
authors.affiliation: Division of Geomagnetism, DTU Space, Technical University of Denmark, Lyngby DK-2800, Denmark.
authors.forename: Christopher C
authors.identifier: http://orcid.org/0000-0002-4592-2290
authors.initials: CC
authors.lastname: Finlay
authors.affiliation: Dynamique des Fluides Géologiques, Institut de Physique du Globe de Paris, 75238 Paris CEDEX 05, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Aubert
authors.affiliation: ISTerre, Université Grenoble 1, CNRS, 38041 Grenoble CEDEX 9, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gillet
references.citation: Science. 2006 May 12;312(5775):900-2
references.pmid: 16690863
references.citation: Nature. 2013 Oct 10;502(7470):219-23
references.pmid: 24108054
references.citation: Nature. 2012 Apr 11;485(7398):355-8
references.pmid: 22495307
references.citation: Nature. 2010 Dec 9;468(7325):807-10
references.pmid: 21150995
references.citation: Naturwissenschaften. 2006 Nov;93(11):519-42
references.pmid: 16915369
references.citation: Rep Prog Phys. 2013 Sep;76(9):096801
references.pmid: 24004491
references.citation: Nature. 2014 Mar 27;507(7493):484-7
references.pmid: 24670768
references.citation: Nature. 2004 May 13;429(6988):169-71
references.pmid: 15141208