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Séminaire MHD (SEMHD)

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Coherent Structures in Turbulent Accretion Disks
Henrik Latter (ENS/LERMA)

8 février 2010

Simulations of the magneto-rotational instability (MRI) in accretion disks often exhibit coherent structures, whereby the disk fluid splits into countermoving planar jets or ’channels’. The formation and destruction of these channel flows may play a role in the development and saturation of MRI-induced turbulence, on one hand, or on outburst events and other time-dependent accretion behaviour, on the other. I present a general discussion of these flows, in particular showing how they coincide with the fastest growing MRI modes, and that their dominance issues from the remarkable fact that these linear solutions are also approximate nonlinear solutions of the vertically stratified MHD equations. `Run-away’ channel solutions accumulate significant amounts of kinetic and magnetic energy, which are violently released when the channel is destroyed by parasitic instabilities. I also discuss these parasitic modes, and then connect the rise of and fall of singular run-away channels with flaring events in protostellar disks.
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• Latter H.N., Fromang S., Gressel O., "MRI channel flows in vertically-stratified models of accretion disks", MNRAS, submitted.
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Henrik Latter Henrik Latter (ENS/LERMA)

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