Diagnostics of turbulence properties through Velocity Gradient Amplitudes: Theory and Observations.
Based on the properties of magneto-hydrodynamic (MHD) turbulence, the recent development of the Velocity Gradient Technique (VGT) allows observers to trace magnetic field directions using spectroscopic information. In this paper, we explore how the amplitudes of gradients from different observables are correlated to the properties of turbulence in terms of statistical moments. We find there is a very good power-law relationship between the dispersion of gradient amplitudes and sonic Mach Number $M_s$, and the increase of alignments of the gradient amplitudes filaments to the decrease of Alfvenic Mach number $M_A$. The visual and quantitative relation between the shapes of gradient amplitudes to Mach numbers allows us to easily evaluate physical conditions. We illustrate our method in GALFA-HI data and find that the high latitude regions have higher $M_s$ but lower $M_A$, which requires theoretical explanations.
Publisher URL: http://arxiv.org/abs/1802.00024
DOI: arXiv:1802.00024v1
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