2020/07/31 by Jérémie Vidal, Adrian J. Barker
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Astrophysics #Convection #Geomagnetism and Paleomagnetism Studies #Mathematical physics #Mechanics #Omega #Physics #Quantum mechanics #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies #Turbulence #astro-ph.EP #astro-ph.SR #physics.flu-dyn
paper · pdf · doi:10.1093/mnras/staa2239
14 pages, 17 figures, 1 table, published 6 August 2020 in MNRAS
openalex publication_date 2020/08/04 · arxiv created 2020/08/29 · arxiv updated 2020/09/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
ABSTRACT Turbulent convection is thought to act as an effective viscosity in damping equilibrium tidal flows, driving spin and orbital evolution in close convective binary systems. Compared to mixing-length predictions, this viscosity ought to be reduced when the tidal frequency |ωt| exceeds the turnover frequency ωcv of the dominant convective eddies, but the efficiency of this reduction has been disputed. We re-examine this long-standing controversy using direct numerical simulations of an idealized global model. We simulate thermal convection in a full sphere, and externally forced by the equilibrium tidal flow, to measure the effective viscosity νE acting on the tidal flow when |ωt|/ωcv ≳ 1. We demonstrate that the frequency reduction of νE is correlated with the frequency spectrum of the (unperturbed) convection. For intermediate frequencies below those in the turbulent cascade (|ωt|/ωcv ∼ 1−5), the frequency spectrum displays an anomalous 1/ωα power law that is responsible for the frequency reduction νE∝1/|ωt|α, where α < 1 depends on the model parameters. We then get |νE| ∝ 1/|ωt|δ with δ > 1 for higher frequencies, and δ = 2 is obtained for a Kolmogorov turbulent cascade. A generic |νE| ∝ 1/|ωt|2 suppression is next found for higher frequencies within the dissipation range of the convection (but with negative values). Our results indicate that a better knowledge of the frequency spectrum of convection is necessary to accurately predict the efficiency of tidal dissipation in stars and planets resulting from this mechanism.