HR: 0800h
AN: GP21A-0004    [Abstracts]
TI: Rapidly evolving sources of geomagnetic dipole tilt on the core-mantle boundary
AU: * Andrews, D L
EM: dandrews@jhu.edu
AF: Department of Earth and Planetary Science, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218
AU: Amit, H
EM: hagay@jhu.edu
AF: Department of Earth and Planetary Science, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218
AU: Olson, P L
EM: olson@jhu.edu
AF: Department of Earth and Planetary Science, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218
AB: We use high-resolution maps of the geomagnetic field on the core-mantle boundary derived from recent satellite and observatory measurements to delineate the sources of the present-day rapid tilt decrease of the geomagnetic dipole. We find that the magnitude of the tilt (presently 10.3 degrees) is largely controlled by high-intensity, normal polarity magnetic flux structures now beneath the Indian Ocean. We argue that this magnetic flux has been transported from high latitudes toward the equator by a large-scale counterclockwise circulation in the southern hemisphere of the liquid outer core. In contrast, we show that the current episode of tilt decrease, which began about 1965, can be attributed to the advection of two intense magnetic field structures on the core-mantle boundary, one currently residing beneath Southern Africa and the other beneath North America. The interaction of these structures with the core flow geometries induces abrupt motions of the geomagnetic pole. The recent rapid decrease in the dipole tilt, as well as the monotonic decrease in the dipole intensity may suggest a beginning of a full polarity reversal. We also examine core flow inversions based on field models covering longer time-spans. In flow inversions from the four-century model GUFM1, based on historical measurements (Jackson et al., 2000), advective mechanisms are identifiable for the dipole tilt dynamics. Examination of the 7000 year model CALS7K.2, based on archeomagnetic and paleomagnetic data (Korte and Constable, 2005), shows that the dipole drifts significantly faster than magnetic field structures, suggesting that tilt dynamics in this model is dominated by diffusive rather than advective mechanisms. The differences between these last two sets of results are likely due to differences in the basis model's resolution and construction.
DE: 1507 Core processes (1213, 8115)
DE: 1510 Dynamo: theories and simulations
DE: 1535 Reversals: process, timescale, magnetostratigraphy
DE: 1560 Time variations: secular and longer
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005