Abstract

Astrophysical outflows are seen in objects ranging from compact binaries up to active galactic nuclei, and magnetized accretion disks are the central engines behind these phenomena. Disk turbulence has a profound effect on the evolution of the large-scale magnetic field and hence on the ability of the system to power its outflows. We aim to characterize the turbulence coefficients emerging in local simulations of magnetorotational (MRI) turbulence. We have generalized our diagnostics to the case of novel non-local and non-instantaneous closure relations, accounting for and extended “domain of dependence” in space, and “memory effects” in time. In concrete terms, we obtain Fourier spectra of the effective turbulent transport coefficients as a function of oscillation frequency. These are well approximated by a simple response function, describing a finite-time build-up of the electromotive force (EMF) as a result of a time-variable mean magnetic field. For intermediate timescales, we observe a significant phase lag of the EMF compared to the causing field.