The thermal Prandtl number (ratio of the diffusivity of momentum to the diffusivity of temperature) can affect the nature of stably stratified turbulence in thermally stable layers of planets and stars (e.g. Earth’s stratosphere or the Sun’s radiative zone). While the Prandtl number of air and water is order unity, it can be less than 1e-5 in stellar radiative zones. A sufficiently small Prandlt number can cause thermal diffusion on the small vertical scales of stably stratified turbulence to become significant. Stably stratified turbulence becomes a balance of overdamped waves and non-linearities instead of the classical regime of a balance of internal gravity waves and non-linearities. This affects the local turbulent diffusion of chemicals in stellar radiative zones.
Hydrodynamic Turbulence in Stellar Radiative Zones
The Rayliegh-Taylor instability in a collisional plasma with an initially weak seed magnetic field can amplify the magnetic energy to equipartition with the kinetic energy through the small-scale dynamo. We developed a scaling theory of the dynamo process and tested the theory with the Athena++ code. In application to the turbulent phase of merging binary neutron stars, the theory predicts that the dynamo is fast enough to generate strong small scale magnetic fields in the Rayliegh-Taylor like turbulence of the outer regions of the final neutron star.