  Aims: We study the changes in the properties of turbulence driven by the
magnetorotational instability in a shearing box, as the computational domain
size in the radial direction is varied relative to the height Methods: We
perform 3D simulations in the shearing box approximation, with a net magnetic
flux, and we consider computational domains with different aspect ratios
Results: We find that in boxes of aspect ratio unity the transport of angular
momentum is strongly intermittent and dominated by channel solutions in
agreement with previous work. In contrast, in boxes with larger aspect ratio,
the channel solutions and the associated intermittent behavior disappear.
Conclusions: There is strong evidence that, as the aspect ratio becomes larger,
the characteristics of the solution become aspect ratio independent. We
conclude that shearing box calculations with aspect ratio unity or near unity
may introduce spurious effects.
