Summary: Physics of the Earth and Planetary Interiors 147 (2004) 125
Helical core flow from geomagnetic secular variation
Hagay Amit, Peter Olson
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218, USA
Received 11 October 2003; received in revised form 2 February 2004; accepted 23 February 2004
Fluid flow below the core-mantle boundary is inferred from geomagnetic secular variation data, assuming frozen magnetic flux
and a new physical assumption termed helical flow, in which the tangential divergence correlates with the radial vorticity. Helical
flow introduces streamfunction diffusion and removes non-uniqueness in the inversion of the magnetic induction equation. We
combine helical flow with tangential geostrophy and compare the following physical assumptions: tangential geostrophy, strong
helicity, weak helicity and columnar flow, using geomagnetic field models from the 2000 Oersted and 1980 Magsat satellites.
Our solutions contain some features found in previous core flow models, such as large mid-latitude vortices, westward drift in
most of the southern hemisphere, and suggested polar vortices. However, our solutions contain significantly more flow along
contours of the radial magnetic field than previous core flow models.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Helical flow; Secular variation; Geomagnetic field; Core-mantle boundary; Frozen flux; Tangential geostrophy
Mapping the flow in Earth's liquid outer core places
constraints on the geodynamo, the thermal structure of
the core, and the nature of core-mantle coupling. Geo-