Flows and dynamos in a model of stellar radiative zones

Abstract

Stellar radiative zones are typically assumed to be motionless in standard models of stellar structure but there is sound theoretical and observational evidence that this cannot be the case. We investigate by direct numerical simulations a three-dimensional and time-dependent model of stellar radiation zones consisting of an electrically conductive and stably stratified anelastic fluid confined to a rotating spherical shell and driven by a baroclinic torque. As the baroclinic driving is gradually increased a sequence of transitions from an axisymmetric and equatorially symmetric time-independent flow to flows with a strong poloidal component and lesser symmetry are found. It is shown that all flow regimes characterised by significant non-axisymmetric components are capable of generating a self-sustained magnetic field. As the value of the Prandtl number is decreased and the value of the Ekman number is decreased, flows become strongly time dependent with progressively complex spatial structure and dynamos can be generated at lower values of the magnetic Prandtl number.