  We present a number of statistical tools for obtaining studying turbulence in
molecular clouds and diffuse interstellar medium. For our tests we used of
three-dimensional 512 cube compressible MHD isothermal simulations performed
for different sonic and Alfvenic Mach numbers. We introduce the bispectrum, a
new tool for statistical studies of the interstellar medium which, unlike an
ordinary power spectrum of turbulence, preserves the phase information of the
stochastic field. We show that the bispectra of the 3D stochastic density field
and of column densities, available from observations, are similar. We use the
bispectrum technique to define the role of non-linear wave-wave interactions in
the turbulent energy cascade. We also obtained the bispectrum function for
density and column densities with varying magnetic field strength. Larger
values of sonic Mach number result in increased correlations for modes with
different wavenumbers. This effect becomes more evident with increasing
magnetic field intensity. In addition to the bispectrum, we calculated the 3rd
and 4th statistical moments of density and column density, namely, skewness and
kurtosis, respectively. We found a strong dependence of skewness and kurtosis
with the sonic Mach number. In particular, as this number increases, so does
the asymmetry of the density distribution. We also studied the correlations of
2D column density with dispersion of velocities and magnetic field, as well as
the correlations of 3D density with magentic and kinetic energy and Alfven Mach
number for comparison. Our results show that column density is linearly
correlated with magnetic field for high sonic Mach number. This trend is
independent of the turbulent kinetic energy and can be used to characterize
inhomogeneities of physical properties in low density clumps in the ISM.
