Baroclinic Instability

Contact: N. Raettig

Recent years have shown that accretion disks around young stars have extended regions, which are too low ionized to couple to magnetic fields and thus the nature of the underlying turbulence cannot be exclusively magnetic. We also found that disks have in general a baroclinic density and temperature structure which means that a typical disk is radially buoyant and has a vertical velocity gradient also known as thermal wind. The radial temperature structure and thus the radial entropy and pressure stratification are determined by the combined influence of stellar irradiation, internal viscous heating and internal radiative heat transport via radiation. If the heat transport in such a baroclinic disk has an effective thermal relaxation time of 0.1-100 orbits, then a so called Subcritical Baroclinic Instability (SBI) will amplify small vortices to giant anti-cyclons that will have strong influence on disk evolution and on planet formation via the efficient concentration of dust.

Vorticity profile in the midplane of a protoplanetary disk. Anticyclonic vortices are amplified by baroclinic feedback.

Vorticity profile ωz and local dust to gas ratio ε for St=0.05 particles. The particles accumulate inside the vortex very efficiently. The local dust do gas ratio is increased above 1. Therefore the streaming instability of particles and their back-reaction onto the gas (visible as the high vorticity regions inside the vortex) are important. The streaming instability is as first step towards gravitational collapse and thus towards planetesimal formation.

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Last modified: February 19 2013 03:52:08