Numerical and experimental investigation of shear-driven inertial oscillations in an Earth-like geometry

Inertial waves and small-scale turbulence are inevitable consequences of rapid rotation and low viscosity in the Earth’s core. We use numerical simulations and experiments to investigate the influence of waves and turbulence on the large-scale flow of an electrically conducting fluid in a spherical annulus. The large-scale flow is driven by shear between the inner-core and outer-core boundaries in the presence of a vertical magnetic field. The rotation rates of the inner and outer boundaries are denoted by Ωi and Ωo, respectively, which define a Rossby number Ro = (Ωi − Ωo)/Ωo. We focus on small negative values (−1 < Ro < 0), where inertial modes have been previously reported in the experiments. Inertial modes are also identified in the simulations at sufficiently low Ekman number. Good agreement with the experiments is obtained for both the spatial structure and frequency of the inertial modes. The experimental results provide an important benchmark for the simulations, while the simulations provide detailed information about the flow, assisting in the interpretation of the experiments. We find that the magnetic field suppresses small-scale flow that would otherwise be present if the sole source of dissipation was due to fluid viscosity.