Karsten Dittrich, Hubert Klahr, Anders Johansen
Recent numerical simulations have shown long lived axisymmetric sub- and super-Keplerian flows in protoplanetary disks. These zonal flows are found in local as well as global simulations of disks unstable to the magneto-rotational instability. This paper investigates the strength and life-time of zonal flows and the resulting long-lived gas over- and under-densities as well as particle concentrations as functions of the azimuthal and radial size of the local shearing box. Changes in the azimuthal box size do not affect the zonal flow features. But with longer radial box sizes the strength and life-time of zonal flows increases. Our simulations support earlier results that zonal flows have a natural radial length scale of 5 to 7 gas pressure scale heights. For the first time, the reaction of dust particles in MHD simulation boxes with strong zonal flows are studied. We show that $\St = 0.1$ particles (of some centimeters in size if at $5 \textrm{AU}$ in a MMSN) reach a hundred-fold higher density than initially. No particle feedback on the gas and no self-gravity is considered. This opens the path for particles of $\St = 0.1$ and dust-to-gas ratio of 0.01 or for particles of $\St \geq 0.5$ and dust-to-gas ratio $10^{-4}$ to still reach densities to trigger the streaming instability and thus gravoturbulent formation of planetesimals.
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http://arxiv.org/abs/1211.2095
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