HR: 1340h
AN: GP33A-0923    [Abstracts]
TI: Effects of thermally heterogeneous structure in the lowermost mantle on the geomagnetic field strength
AU: * Takahashi, F
EM: futoshi@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
AU: Tsunakawa, H
EM: htsuna@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
AU: Matsushima, M
EM: mmatsush@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
AU: Mochizuki, N
EM: n.mochizuki@aist.go.jp
AF: Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, 305-8567, Japan
AU: Honkura, Y
EM: yhonkura@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8551, Japan
AB: 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.
DE: 1507 Core processes (1213, 8115)
DE: 1510 Dynamo: theories and simulations
DE: 1521 Paleointensity
DE: 5440 Magnetic fields and magnetism
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting