Core precession: flow structures and energy

Experiments using a precessing liquid-filled oblate spheroid with elliptici ty (a - b)/a =1/400 extend and clarify earlier research. They yield flow da ta useful for estimating flows in the Earth's liquid core. Observed flows i llustrate and confirm a nearly rigid liquid sphere with retrograde drift an d lagging a cavity (mantle) axis in precession. The similarities of the obs erved lag angle with that computed for a rigid sphere, and earlier energy d issipation research both support the use of a rigid sphere analytical model to predict energy dissipation and first-order flow within the core-mantle boundary (CMB). Second-order boundary layer and interior cylindrical flow s tructures also are photographed and measured. Interior flows are never turb ulent or unstable at near-Earth parameters, although complex and transient flow patterns are observed within the boundary layer. Other mechanisms prop osed to explain net heat loss from the Earth and maintenance of the geodyna mo typically require acceptance of some critical but unproven premise. Prec ession and CMB configuration are known with certainty and precision. Analyt ical difficulties have been the obstacle. Experiments illustrate the conseq uences of precession and ellipticity, provide criteria for validating analy tical and numerical models, and may yield direct knowledge of the Earth's d eep interior with careful scaling.