New scaling for the alpha effect in slowly rotating turbulence

Abstract

Using simulations of slowly rotating stratified turbulence, we show that the alpha effect responsible for the generation of astrophysical magnetic fields is proportional to the logarithmic gradient of kinetic energy density rather than that of momentum, as was previously thought. This result is in agreement with a new analytic theory developed in this paper for large Reynolds numbers. Thus, the contribution of density stratification is less important than that of turbulent velocity. The alpha effect and other turbulent transport coefficients are determined by means of the test-field method. In addition to forced turbulence, we also investigate supernova-driven turbulence and stellar convection. In some cases (intermediate rotation rate for forced turbulence, convection with intermediate temperature stratification, and supernova-driven turbulence) we find that the contribution of density stratification might be even less important than suggested by the analytic theory.

10 pages, 9 figures, revised version, Astrophys. J., in press

References in corpus (9)

• Mean-field concept and direct numerical simulations of rotating magnetoconvection and the geodynamo
• Direct simulations of a supernova-driven galactic dynamo
• Large-scale dynamos in turbulent convection with shear
• Scale dependence of alpha effect and turbulent diffusivity
• Alpha effect and turbulent diffusion from convection
• The supernova-regulated ISM. II. The mean magnetic field
• Memory effects in turbulent transport
• Effect of the radiative background flux in convection
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