The Millennium Arecibo 21-cm Absorption Line Survey. IV. Statistics of   Magnetic Field, Column Density, and Turbulence
  We discuss observations of the magnetic field, column density, and turbulence in the Cold Neutral Medium (CNM). The observed quantities are only indirectly related to the intrinsic astronomical ones. We relate the observed and intrinsic quantities by relating their univariate and bivariate probability distribution functions (pdfs). We find that observations of the line-of-sight component of magnetic field do not constrain the pdf of the total field very well, but do constrain the median value of the total field.   In the CNM, we find a well-defined median magnetic field 6.0 +/-1.8 microGauss. The CNM magnetic field dominates thermal motions. Turbulence and magnetism are in approximate equipartition. We find the probability distribution of HI column density Nperp in the sheets closely follows Nperp^-1 over a range of two orders of magnitude, 0.026 < Nperp < 2.6 (times 10^20 cm^-2). The bivariate distributions are not well enough determined to constrain structural models of CNM sheets. 
Carl Heiles, T. H. Troland