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Session 40 - The Interstellar Medium.
Display session, Tuesday, June 09
We have studied new 3D simulations of the MHD Kelvin-Helmholtz instability in a periodic section of a strongly sheared flow. Our focus is on the role of magnetic fields that are too weak to stabilize the linear growth of the instability, but that may still influence its nonlinear evolution. We consider media that are initially uniform except for the shear layer, which contains a velocity transition equal to the local sound speed. Alfvenic Mach numbers from about 4 to over 10^3 were examined. The initial magnetic field lies parallel to the shear plane, but is oblique to the flow direction, at an angle of 30 degrees. This work extends previous 2D simulations reported in the Astrophysical Journal (Frank etal 1995, vol 460, p 777; Jones etal 1997, vol 482, p 230). Consistent with the earlier results, we find that even initially very weak magnetic fields have the ability to dynamically modify the flows through tension developed by vortex formation and stretching. During reconnection the magnetic and velocity fields are dynamically aligned, so that the flow is self-organized. In the absense of magnetic fields, or for extremely weak fields the outcome of the instability is turbulence. However, for Alfvenic Mach numbers less than about 50 (plasma \beta < 2000) we find that a broadened shear layer exists to the end of our simulations.
This work is supported by KOSEF in Korea, and by the NSF, NASA and the Minnesota Supercomputing Institute in the USA.
Program listing for Tuesday