Researchers have long assumed that Earth's core processes occur within a nearly perfect spherical shell and that this condition is sufficient to explain most of the geodetic and geomagnetic observations. However, seismic investigations and mantle convection simulations suggest that the core-mantle boundary contains variations in shape and temperature, creating a heterogeneous boundary. Recent models suggest that boundary heterogeneities may control both the large-scale generation of the Earth's magnetic field (e.g., Christensen and Olson, 2003) and the exchange of angular momentum between the mantle and core (e.g., Hide, 1969; Jault, 2003). In fact, the effects of heterogeneous boundaries may be one of the most important controlling factors influencing Earth's core processes. However, there are few laboratory experiments that have been conducted to study the effects of thermal heterogeneity (Sumita and Olson, 1999; 2002) and none to study the effects of topographic heterogeneity.
In this study, the investigators will measure the effects of heterogeneous boundary topography on core flows, using coupled laboratory and numerical experiments. The results will allow a test of whether core flow can become locked in place by topographic bumps. They will also use our results to estimate the viscous and pressure torques at the core-mantle boundary, which affect the rotation of the Earth and variations in the length of day (Jault and Lemouel, 1989, 1999; Kuang and Bloxham, 1993; Kuang and Chao, 2001).
