Paper in Press
JOURNAL OF GEOPHYSICAL RESEARCH, doi:10.1029/2011JB009014
Precessional states in a laboratory model of the Earth's core
- Precession-induced flows observed in a 3-m diameter model of the Earth's core
- Shear layer scaling differs from numerical expectations
- Dissipation in shear layers could reconcile VLBI measurements and nutation model
A water-filled three-meter diameter spherical shell, geometrically similar to the Earth's core, shows precessionally forced flows. The precessional torque is supplied by the daily rotation of the laboratory by the Earth. We identify the precessionally forced flow to be primarily the spin-over inertial mode, i.e., a uniform vorticity flow whose rotation axis is not aligned with the sphere's rotation axis. A systematic study of the spin-over mode is carried out, showing that the amplitude depends on the ratio of precession to rotation rates, in qualitative agreement with Busse's laminar theory (Busse, F. (1968), JFM, 33, 739-751). We find its phase differs significantly though, likely due to topographic effects. At high rotation rates, free shear layers are observed. Comparison with previous computational studies and implications for the Earth's core are discussed.
Received 9 November 2011; accepted 15 February 2012.
Citation: (2012), Precessional states in a laboratory model of the Earth's core, J. Geophys. Res., doi:10.1029/2011JB009014, in press.