– Niels Bohr Institute - University of Copenhagen

Sensitivity of the magnetorotational instability to the shear parameter in stratified simulations

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Farrukh Nauman, Eric G. Blackman

The magnetorotational instability (MRI) is a shear instability and thus its sensitivity to the shear parameter q = -d ln Ω/d ln r is of interest to investigate. Motivated by astrophysical discs, most (but not all) previous MRI studies have focused on the Keplerian value of q = 1.5. Using simulation with eight vertical density scaleheights, we contribute to the subset of studies addressing the effect of varying q in stratified numerical simulations. We discuss why shearing boxes cannot easily be used to study q > 2 and thus focus on q <2. As per previous simulations, which were either unstratified or stratified with a smaller vertical domain, we find that the q dependence of stress for the stratified case is not linear, contrary to the Shakura-Sunyaev model. We find that the scaling agrees with Abramowicz, Brandenburg & Lasota who found it to be proportional to the shear to vorticity ratio q/(2 - q). We also find however that the shape of the magnetic and kinetic energy spectra are relatively insensitive to q and that the ratio of Maxwell stress to magnetic energy ratio also remains nearly independent of q. This is consistent with a theoretical argument in which the rate of amplification of the azimuthal field depends linearly on q and the turbulent correlation time τ depends inversely on q. As such, we measure the correlation time of the turbulence and find that indeed it is inversely proportional to q.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Pages (from-to)2102-2109
StatePublished - 1 Jan 2015
Externally publishedYes

    Research areas

  • accretion, accretion discs, instabilities, MHD, turbulence

ID: 166633254