Precessional states in a laboratory model of the Earth's core

A water-filled three-meter diameter spherical shell built as a model of the Earth's core shows evidence of precessionally induced flows. We identified the flow to be primarily the spin-over inertial wave mode, i.e., a uniform vorticity flow whose rotation axis is not aligned with the container's rotation axis. The mode's amplitude dependence on the Poincar\'{e} number is in qualitative agreement with Busse's laminar theory (\textit{JFM} \textbf{33}:739-751, 1968) while its phase differs significantly, perhaps due to topographic effects. At high rotation rates free shear layers concentrating most of the kinetic energy of the mode have been observed. Comparison with previous computational studies and implications for the Earth's core are discussed.