HR: 15:00h
AN: S12D-05    [PDF]
TI: Prograde and Retrograde Free Core Nutations Observed with VLBI
AU: * Palmer, A
EM: palmer@core.yorku.ca
AF: York University, 4000 Keele Street, Toronto, ONT M3J 1P3 Canada
AU: Smylie, D
EM: doug@core.yorku.ca
AF: York University, 4000 Keele Street, Toronto, ONT M3J 1P3 Canada
AB: VLBI nutation measurement series from Goddard Space Flight Center and the United States Naval Observatory have been analyzed for Free Core Nutation resonances. Our analysis implements Singular Value Decomposition to solve the least squares problem of fitting the Discrete Fourier Tranform to the non-equispaced VLBI nutation observations. A novel feature of our procedure is to use the Parseval relation to determine the number of singular values of the coefficient matrix to be eliminated. We report the observation for the first time of the prograde mode predicted by Jiang (1993). The long series of observations allow the determination of the time evolution of the Free Core Nutation. We report a ring down of the large retrograde mode. In addition to providing a value for the viscosity just below the Core-Mantle Boundary, it suggests an impulse excitation rather than a continuous excitation. The interest of one of us (DES) in the rotational dynamics of Earth's core was stimulated by a conversation with Don Anderson about the possibility of the inner core being titled with respect to the shell and that a gravitational restoring torque might result. Indeed a large gravitational coupling exists and plays an important role in the rotational dynamics of the inner and outer cores.
DE: 1210 Diurnal and subdiurnal rotational variations
DE: 1212 Earth's interior--composition and state (8105)
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 7207 Core and mantle
DE: 9820 Techniques applicable in three or more fields
SC: Seismology [S]
MN: 2003 Fall Meeting