On characterizing non-locality and anisotropy for the magnetorotational instability
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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.
Originalsprog | Engelsk |
---|---|
Tidsskrift | Monthly Notices of the Royal Astronomical Society |
Vol/bind | 441 |
Udgave nummer | 3 |
Sider (fra-til) | 1855-1860 |
ISSN | 0035-8711 |
DOI | |
Status | Udgivet - 1 jul. 2014 |
Eksternt udgivet | Ja |
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