Spectral properties of compressible magnetohydrodynamic turbulence from numerical simulations

We analyze the spectral properties of driven, supersonic, compressible, magnetohydrodynamic (MHD) turbulence obtained via high-resolution numerical experiments, for application to understanding the dynamics of giant molecular clouds. Via angle-averaged power spectra, we characterize the transfer of energy from the intermediate, driving scales down to smaller dissipative scales and also present evidence for inverse cascades that achieve modal equipartition levels on larger spatial scales. Investigating compressive versus shear modes separately, we evaluate their relative total power and find that as the magnetic field strength decreases, (1) the shear fraction of the total kinetic power decreases and (2) slopes of power-law fits over the inertial range steepen. To relate to previous work on incompressible MHD turbulence, we present qualitative and quantitative measures of the scale-dependent spectral anisotropy arising from the shear Alfven cascade and show how these vary with changing mean magnetic field strength. Finally, we propose a method for using anisotropy in velocity centroid maps as a diagnostic of the mean magnetic field strength in observed cloud cores.