Effects of thermally heterogeneous structure in the lowermost mantle on the geomagnetic field strength

Details Effects of thermally heterogeneous structure in the lowermost mantle on the geomagnetic field strength Effects of thermally heterogeneous structure in the lowermost mantle on the geomagnetic field strength

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmgp33a0923t&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #GP33A-0923

Physics

1507 Core Processes (1213, 8115), 1510 Dynamo: Theories And Simulations, 1521 Paleointensity, 5440 Magnetic Fields And Magnetism, 8147 Planetary Interiors (5430, 5724, 6024)

Scientific paper

We have conducted a study of numerical dynamos in a rapidly rotating spherical shell with prescribed non- uniform heat flux patterns at the outer boundary to examine effects of thermal structure at the core-mantle boundary (CMB) on the geodynamo, especially on the magnetic field strength. We found that strong heterogeneity of heat flux with quatorial symmetry enhances strength of the dipolar magnetic field for an Ekman number, E = 10-5, contrary to the case E = 10-4. Strong magnetic fields are generated in the fluid core off the equatorial plane beneath high heat flux regions, while moderate magnetic fields are maintained beneath low heat flux regions. The equatorially anti- symmetric heat flux distribution at the CMB affects the magnetic dipole axis through generation of the equatorially symmetric magnetic field. The boundary-induced thermal wind has strong influence on the flow structure and on the magnetic field intensity. These results suggest that thermally heterogeneous structure of the lowermost mantle might give rise to an anomalously strong geomagnetic field such as that during the Cretaceous Normal Superchron.

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