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Internally-driven inertial waves in geodynamo simulations

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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.

This talk is part of the DAMTP Astrophysics Seminars series.

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