Abstract

Inertial waves are oscillations in a rotating fluid, such as the Earth’s outer core, which result from the restoring action of the Coriolis force and conservation of angular momentum. Particularly important are the low-frequency inertial waves that are known to create Taylor columns above a moving body in a rotating tank. They also create columnar flow structures above/below a localized layer of buoyancy.

We report, for the first time, internally-driven inertial waves triggered by buoyant anomalies near the equator in a strongly-forced geodynamo simulation at Ra/Ra_c=42 and E=3×10^{-5}. Using the vertical acceleration as a diagnostic for wave-fronts, we find that a horizontal movement of buoyant anomalies near the equator is well-correlated with a corresponding movement far from the equator. Moreover, we find that the slopes observed in the time-series of vertical acceleration match closely with those expected from the group speed of low-frequency inertial waves. The azimuthally-averaged spectrum of vertical acceleration lies in the inertial wave frequency range. Our results suggest that the columnar flow in the rotation-dominated core, an important ingredient for the maintenance of a dipolar magnetic field, is maintained on a fast-time scale by internally-driven inertial waves, and not by boundary-driven Busse rolls as previously thought. The dynamical role of inertial waves, particularly with regards to their helicity segregation characteristic, is under investigation.