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Title:Non-ideal MHD turbulent decay in molecular clouds
Authors:Downes, T.P., O'Sullivan, S., 2009
Abstract: It is well known that nonideal magnetohydrodynamic (MHD) effects are important in the dynamics of molecular clouds: both ambipolar diffusion and possibly the Hall effect have been identified as significant. We present the results of a suite of simulations with a resolution of 5123 of turbulent decay in molecular clouds, incorporating a simplified form of both ambipolar diffusion and the Hall effect simultaneously. The initial velocity field in the turbulence is varied from being super-Alfvénic and hypersonic, through to trans-Alfvénic but still supersonic. We find that ambipolar diffusion increases the rate of decay of the turbulence increasing the decay from t -1.25 to t -1.4. The Hall effect has virtually no impact in this regard. The power spectra of density, velocity, and the magnetic field are all affected by the nonideal terms, being steepened significantly when compared with ideal MHD turbulence with exponents. The density power-spectra components change from ~1.4 to ~2.1 for the ideal and nonideal simulations respectively, and power spectra of the other variables all show similar modifications when nonideal effects are considered. Again, the dominant source of these changes is ambipolar diffusion rather than the Hall effect. There is also a decoupling between the velocity field and the magnetic field at short length scales. The Hall effect leads to enhanced magnetic reconnection, and hence less power, at short length scales. The dependence of the velocity dispersion on the characteristic length scale is studied and found not to be power law in nature.
ICHEC Project:Turbulence in molecular clouds: beyond magnetic flux freezing
Publication:The Astrophysical Journal, Volume 701, Issue 2, pp. 1258-1268 (2009). 10.1088/0004-637X/701/2/1258
URL: http://adsabs.harvard.edu/abs/2009ApJ...701.1258D
Keywords: kinematics and dynamics, magnetic fields, methods: numerical, MHD, turbulence
Status: Published

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