Abstract
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. Here we show that the expected entropy gradients in observed accretion disks around young stars are in fact steep enough and that the thermal relaxation times are sufficiently short to allow for efficient amplification of vortices.
Highlights
Klahr and Bodenheimer (2003) [1] introduced the idea that a radial entropy gradient or more precisely a negative square of the radial Brunt-Väisälä frequency N2 can destabilize a Rayleigh stable accretion disk
Recent years have shown that accretion disks around young stars have extended regions, which are too low ionized to couple to magnetic fields and the nature of the underlying turbulence cannot be exclusively magnetic
We show that the expected entropy gradients in observed accretion disks around young stars are steep enough and that the thermal relaxation times are sufficiently short to allow for efficient amplification of vortices
Summary
Klahr and Bodenheimer (2003) [1] introduced the idea that a radial entropy gradient or more precisely a negative square of the radial Brunt-Väisälä frequency N2 can destabilize a Rayleigh stable accretion disk. The combined condition of strong enough perturbations and sufficiently large Reynolds numbers led them to the conclusion that the Baroclinic Instability in accretions disks is a non-linear feature Relaxation time of 0.1–100 orbits, a so called Subcritical Baroclinic Instability (SBI) will amplify small vortices to giant anti-cyclons (see Fig. 1) as has been shown in local 3D shearing sheat simulations by Lesur and Papaloizou (2000) [5] and Lyra and Klahr (2011) [6] These vortices will have strong influence on disk evolution and on planet formation via the efficient concentration of dust.
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