HR: 0800h
AN: GP11D-0852    [Abstracts]
TI: Azimuthal flows in the Earth's core and changes in length of day at millennial timescales
AU: * Dumberry, M
EM: dumberry@mail.geophysics.harvard.edu
AF: Department of Earth & Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Bloxham, J
EM: jeremy\_bloxham@harvard.edu
AF: Department of Earth & Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138 United States
AB: In this work, we attempt to constrain a part of the dynamics in the Earth's fluid core at millennial timescales by using observed variations in the Earth's rotation and geomagnetic field over the last three Millennia. Variations in length of day reconstructed from ancient records of eclipses contain an oscillating component with a periodicity of roughly 1500 years. A part of the time-dependent variations observed in archaeomagnetic field models consist of episodic eastward and westward drifts with a similar periodicity. Using standard inversion techniques, we obtain time-dependent azimuthal flows at the surface of the core that can explain this part of the archaeomagnetic field variations. We show that these flows are consistent with the changes in core angular momentum required to produce the observed length of day variations provided there exists a shear in velocity in the axial direction inside the core. We interpret these time-dependent azimuthal flows as fluctuations in thermal and magnetic winds and discuss the implications for the geodynamo and core-mantle coupling at millennial timescales.
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 1239 Rotational variations
DE: 1507 Core processes (8115)
DE: 1510 Dynamo theories
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting