Sensitivity of the magnetorotational instability to the shear parameter in stratified simulations
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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.
Originalsprog | Engelsk |
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Tidsskrift | Monthly Notices of the Royal Astronomical Society |
Vol/bind | 446 |
Udgave nummer | 2 |
Sider (fra-til) | 2102-2109 |
ISSN | 0035-8711 |
DOI | |
Status | Udgivet - 1 jan. 2015 |
Eksternt udgivet | Ja |
ID: 166633254