Studying Interstellar Turbulence Driving Scales using the Bispectrum
  We demonstrate the utility of the bispectrum, the Fourier three-point
correlation function, for studying driving scales of magnetohydrodynamic (MHD)
turbulence in the interstellar medium. We calculate the bispectrum by
implementing a parallelized Monte Carlo direct measurement method, which we
have made publicly available. In previous works, the bispectrum has been used
to identify non-linear scaling correlations and break degeneracies in
lower-order statistics like the power spectrum. We find that the bicoherence, a
related statistic which measures phase coupling of Fourier modes, identifies
turbulence driving scales using density and column density fields. In
particular, it shows that the driving scale is phase-coupled to scales present
in the turbulent cascade. We also find that the presence of an ordered magnetic
field at large-scales enhances phase coupling as compared to a pure
hydrodynamic case. We therefore suggest the bispectrum and bicoherence as tools
for searching for non-locality for wave interactions in MHD turbulence.
