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Turbulence and angular momentum transport in accretion disks remains a topicof debate. With the realization that dead zones are robust features ofprotoplanetary disks, the search for hydrodynamical sources of turbulencecontinues. A possible source is the baroclinic instability (BI), which has beenshown to exist in unmagnetized non-barotropic disks. We present shearing boxsimulations of baroclinicly unstable, magnetized, 3D disks, in order to assessthe interplay between the BI and other instabilities, namely themagneto-rotational instability (MRI) and the magneto-elliptical instability. Wefind that the vortices generated and sustained by the baroclinic instability inthe purely hydrodynamical regime do not survive when magnetic fields areincluded. The MRI by far supersedes the BI in growth rate and strength atsaturation. The resulting turbulence is virtually identical to an MRI-onlyscenario. We measured the intrinsic vorticity profile of the vortex, findinglittle radial variation in the vortex core. Nevertheless, the core is disruptedby an MHD instability, which we identify with the magneto-elliptic instability.This instability has nearly the same range of unstable wavelengths as the MRI,but has higher growth rates. In fact, we identify the MRI as a limiting case ofthe magneto-elliptic instability, when the vortex aspect ratio tends toinfinity (pure shear flow). We conclude that vortex excitation andself-sustenance by the baroclinic instability in protoplanetary disks is viableonly in low ionization, i.e., the dead zone. Our results are thus in accordancewith the layered accretion paradigm. A baroclinicly unstable dead zone shouldbe characterized by the presence of large-scale vortices whose cores areelliptically unstable, yet sustained by the baroclinic feedback. As magneticfields destroy the vortices and the MRI outweighs the BI, the active layers areunmodified.

astronomy and astrophysics

The baroclinic instability in the context of layered accretion.  Self-sustained vortices and their magnetic stability in local compressible  unstratified models of protoplanetary disks