Summary: Available online at www.sciencedirect.com
Physics of the Earth and Planetary Interiors 166 (2008) 226­238
Geomagnetic dipole tilt changes induced by core flow
Hagay Amita,, Peter Olsonb
a Equipe de G´eomagn´etisme, Institut de Physique du Globe de Paris (Institut de Recherche associ´e au CNRS et `a l'Universit´e Paris 7),
4 Place Jussieu, 75252 Paris Cedex 05, France
b Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA
Received 20 April 2007; received in revised form 26 October 2007; accepted 22 January 2008
Abstract
The tilt of the geomagnetic dipole decreased from about 11.7
in 1960 to 10.5
in 2005, following more than a century when it remained nearly
constant. The recent poleward motion of the dipole axis is primarily due to a rapid decrease in the equatorial component of the dipole moment
vector. Using maps of the equatorial dipole moment density and its secular change derived from core field models, we identify regions on the
core­mantle boundary where the present-day tilt decrease is concentrated. Among the possible causes of equatorial dipole moment change on
the core­mantle boundary, tangential magnetic diffusion is negligible on these time scales, and although radial magnetic diffusion is potentially
significant, the rapid changes in equatorial moment density indicate it is not the dominant mechanism. We show that magnetic flux transport can
account for most of the observed equatorial dipole moment change. Frozen-flux core flow models derived from geomagnetic secular variation reveal
a nearly balanced pattern of advective sources and sinks for the equatorial dipole moment below the core­mantle boundary. The recent tilt decrease
originates from two advective sinks, one beneath Africa where positive radial magnetic field is transported westward away from the equatorial

Source: Amit, Hagay - Institut de Physique du Globe de Paris

Collections: Geosciences