2021/03/02 by B A Buffett, B. A. Buffett
Biochemistry, Genetics and Molecular Biology · Engineering · Physics and Astronomy · #Fluid Dynamics and Turbulent Flows #Geomagnetism and Paleomagnetism Studies #Solar and Space Plasma Dynamics
paper · doi:10.1093/gji/ggab088
openalex publication_date 2021/03/02 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
SUMMARY Ekman layers develop at the boundaries of the Earth’s fluid core in response to precession. Instabilities in these layers lead to turbulence when a local Reynolds number, Re, based on the thickness of the Ekman layer, exceeds a critical value. The transition to turbulence is often assessed using experiments for steady Ekman layers, where the interior geostrophic flow is independent of time. Precessionally driven flow varies on diurnal timescales, so the transition to turbulence may occur at a different value of Re. We use 3-D numerical calculations in a local Cartesian geometry to assess the transition to turbulence in precessional flow. Calculations retain the horizontal component of the rotation vector and account for the influence of fluid stratification. The transition to turbulence in a neutrally stratified fluid occurs near Re = 500, which is higher than the value Re = 150 usually cited for steady Ekman layers. However, it is comparable to the nominal value for precessional flow in the Earth. Complications due to fluid stratification or a magnetic field can suppress the transition to turbulence, reducing the likelihood of turbulent Ekman layers in the Earth’s core.