Dynamics of the earth's fluid and solid cores

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The goal of this research is to improve our knowledge of the dynamics in the Earth's fluid core and its interaction with the inner core and mantle. Though the physics describing these systems is complex, progress can be made by focusing on specific aspects of the dynamics. The general approach in this research is to test simple models of the dynamics by investigating whether the predicted variations in the Earth's magnetic field, rotation and gravity field are compatible with actual observations of these quantities. Specific dynamical aspects of the Earth's core that are studied include torsional oscillations, a core flow with a cylindrical geometry detected in the magnetic data and the Earth's rotation variations. Questions remain as to whether these oscillations are free modes, like a mass suspended by a spring, or forced motions by the underlying dynamics. I will study the nature of this flow by numerical modelling. Another project is to investigate the cause of the so-called "geomagnetic jerks", which are magnetic variations occurring on a timescale of approximately 1 year. I propose to study the action between flows and magnetic field near the surface of the core and to test which scenario is most compatible with observations. Using the same framework, I will also study the cause of the so-called "archaeomagnetic jerks", which are observed over a much longer timescale of millennia. Over the same timescale, archaeomagnetic observations will be surveyed to determine whether the motions of magnetic field features near the equator of the CMB observed over the past few centuries have been a feature of the geodynamo for much longer in the past. Finally, two projects involve the role of the inner core in the rotational dynamics of the Earth. First, observed variations in the Earth's rotation rate with a period of 6 years are interpreted to represent axial oscillations between the inner core and mantle. Gravity field and magnetic field data will be surveyed to find further evidences of this oscillation. In the second project, I will study the dynamics of the flow and magnetic field near the inner core, through their ability to imprint a torque on the latter which leads to a tilt of its figure and causes a change in the direction of Earth's rotation.