Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp43a0797k&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #GP43A-0797
Other
1500 Geomagnetism And Paleomagnetism, 1507 Core Processes (1213, 8115), 4490 Turbulence (3379, 4568, 7863)
Scientific paper
An improved understanding of the geodynamo has fundamental importance in planetary science, with relevance to geomagnetic forecasting as well as predicting behaviors of other planetary dynamos~--- Mercury, Ganymede, and newfound exoplanets, for example. One recent experiment (Bourgoin et~al., New J. Phys 8 12:329, 2006) achieved self-generation of magnetic fields after the addition of ferromagnetic (soft iron) impellers. The geometry of that experiment greatly differs from that of a planet, however, and the effects of soft iron are not well understood. We present experimental observations of magnetic induction in an Earth-like geometry, both with a copper inner sphere and with a soft iron inner sphere. Our experiment is a spherical Couette cell, 60~cm in diameter, with a 20~cm inner sphere, and liquid sodium filling the gap. We drive fluid motions via differential rotation of the two spheres. Applying an axial magnetic field, we observe the magnetic fields induced by those fluid motions. We find that some characteristic behaviors, such as Coriolis-restored inertial modes, are present in both configurations. Other behaviors arise only when a soft iron sphere is present, including sudden onsets of axisymmetric modes causing large angular momentum fluxes. Our observations may suggest the mechanisms by which soft iron can enable dynamo action. The support of NSF Earth Sciences is greatly acknowledged.
Kelley Douglas H.
Lathrop Daniel P.
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