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SUMMARY:Instability mechanism and vortex disruption in magnetohydrodynamic
  shear flows - Julian Mak (Edinburgh)
DTSTART:20161010T150000Z
DTEND:20161010T160000Z
UID:TALK67373@talks.cam.ac.uk
CONTACT:Robert Teed
DESCRIPTION:The problem of linear stability and nonlinear evolution of mag
 netohydrodynamic (MHD) shear flows in two-dimensional\, homogeneous\, inco
 mpressible MHD is revisited. In the equivalent hydrodynamic setting\, the 
 instability mechanism is typically interpreted in terms of the Counter-pro
 pagating Rossby Wave (CRW) mechanism\, and as the instability reaches fini
 te amplitude\, the shear flow rolls up into vortices that\, in a two-dimen
 sional homogeneous system\, is stable and long-lived. The talk will focus 
 on the MHD modifications to the CRW mechanism as well as the potential dis
 ruption of such long-lived vortices from MHD feedback. An estimate based o
 n the scaling arguments of Weiss (1966) is performed which predicts that v
 ortices will be disrupted when M^2 Rm = O(1)\, where M is a measure of the
  initial field strength and Rm is the magnetic Reynolds number. A vortex d
 isruption parameter based on the Okubo--Weiss criterion is utilised to ana
 lyse direct numerical simulations of MHD shear flows\, and the analyses le
 nd support to the theoretical estimate.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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