– Niels Bohr Institute - University of Copenhagen

On characterizing non-locality and anisotropy for the magnetorotational instability

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Farrukh Nauman, Eric G. Blackman

The extent to which angular momentum transport in accretion discs is primarily local or non-local and what determines this is an important avenue of study for understanding accretion engines. Taking a step along this path, we analyse simulations of the magnetorotational instability (MRI) by calculating energy and stress power spectra in stratified isothermal shearing box simulations in several new ways. We divide our boxes in two regions, disc and corona where the disc is the MRI unstable region and corona is the magnetically dominated region. We calculate the fractional power in different quantities, including magnetic energy and Maxwell stresses and find that they are dominated by contributions from the lowest wave numbers. This is even more dramatic for the corona than the disc, suggesting that transport in the corona region is dominated by larger structures than the disc. By calculating averaged power spectra in one direction of k space at a time, we also show that the MRI turbulence is strongly anisotropic on large scales when analysed by this method, but isotropic on small scales. Although the shearing box itself is meant to represent a local section of an accretion disc, the fact that the stress and energy are dominated by the largest scales highlights that the locality is not captured within the box. This helps to quantify the intuitive importance of global simulations for addressing the question of locality of transport, for which similar analyses can be performed.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Pages (from-to)1855-1860
StatePublished - 1 Jul 2014
Externally publishedYes

    Research areas

  • accretion, accretion discs, instabilities, MHD, turbulence

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