Linking mantle convection with rotational dynamics on Earth

Ian Rose and Bruce Buffett University of California, Berkeley A surprising number of features of the solid Earth are aligned with its rotation axis: plate velocities are faster near the equator and may have a net westward drift, the seismically-observed LLSVPs are located equatorially and may have been stable over hundred million year time scales, and large-scale geoid highs reside on the equator. All of these observations suggest that convection and rotation of Earth's mantle are linked, despite the small relative sizes of the rotational forces in Earth's mantle. Coupling of solid-Earth convection and its rotation may be through centrifugal forces on density anomalies in the mantle, gravitational perturbations due to the hydrostatic bulge, changes in the rotation axis due to changes in Earth's moment of inertia, or some combination of the three. We investigate the interplay between convection and rotation using models that fully couple the processes. We accomplish this in the following ways: 1) Earth will tend to rotate about the axis of its maximum moment of inertia. At every time step we solve for this axis and compute the rotational forces accordingly. 2) We implement a true free surface boundary condition with a remeshing algorithm that allows the hydrostatic bulge to adjust dynamically (critical to getting the correct rates of true polar wander). 3) We use Lagrangian tracer particles to represent compositional heterogeneity, as they reduce numerical diffusion and allow for history dependent materials. With these we may represent potentially large contributors to the moment of inertia such as continents and LLSVPs. Here we discuss details of implementation of the model and preliminary results constraining the rate and magnitude of true polar wander on Earth.