Large-scale dynamo action precedes turbulence in shearing box simulations of the magnetorotational instability

• DOI: 10.1093/mnras/stw1619
• Publication Date: 2016-07-07T00:48:07Z
• Authors: Pallavi Bhat; Fatima Ebrahimi; Eric G. Blackman
• Keywords: Wavenumber; Magnetorotational instability; Shearing (physics)

We study the dynamo generation (exponential growth) of large-scale (planar averaged) fields in unstratified shearing box simulations magnetorotational instability (MRI). In contrast to previous studies restricted horizontal (x–y) averaging, we also demonstrate presence when vertical (y–z) averaging is employed instead. By computing space–time planar averaged and power spectra, find action early MRI growth phase – a previously unidentified feature. Non-axisymmetric linear modes with low wavenumbers near that expected maximal growth, amplify exponentially before turbulence high wavenumber fluctuations arise. Thus requires only but not non-linear (as defined by mode–mode coupling). Vertical allows for monitoring evolution field feedback from provides clue as why sustains against turbulent diffusion saturation regime. compute terms mean equations identify individual contributions both types averaging. The obtained are found compare well global quasi-linear analytical analysis Ebrahimi & Blackman. discuss potential implications these new results understanding turbulence.