The origin of Earth's magnetic field is broadly understood to be a consequence of convection in the liquid iron core, yet there is little consensus on the processes involved. Numerical geodynamo models have been remarkably successful in reproducing features of Earth's field at the surface. However, the internal workings of different models can be vastly different. Efforts to distinguish between these possibilities are hampered by a lack of information about the dynamical state of Earth's core. The investigator proposes to use hydromagnetic waves (torsional oscillations) in the core to recover information about the dynamics of the core and boundary regions. The vibrations have observable consequences for fluid flow at the surface of the core, variations in the length of day and changes in the gravity field. Historical and satellite-based observations will be analyzed using a new theoretical framework that relies on methods commonly employed in normal-mode seismlogy. The underlying mathematical model describes the hydromagnetic waves, as well as the accompanying motion of the mantle and inner core. This model will be used to jointly invert observations of flow at the core surface, variations in length of day, and changes in gravity for the internal structure of the magnetic field and convective processes that excite the waves (parameters analogous to earth structure and source mechanism in seismology). Progress in our understanding of the structure and dynamics of Earth's core will provide new insights into the operation and power consumption of the geodynamo. These issues are crucial for understanding the thermal and chemical evolution of our own planet, and perhaps why Venus and Mars evolved so differently.
