  We present an extensive analysis of the 850 microns polarization maps of the
SCUPOL Catalog produced by Matthews et al. (2009), focusing exclusively on the
molecular clouds and star-forming regions. For the sufficiently sampled
regions, we characterize the depolarization properties and the
turbulent-to-mean magnetic field ratio of each region. Similar sets of
parameters are calculated from 2D synthetic maps of dust emission polarization
produced with 3D MHD numerical simulations scaled to the S106, OMC-2/3, W49 and
DR21 molecular clouds polarization maps. For these specific regions the
turbulent MHD regimes retrieved from the simulations, as described by the
turbulent Alfv\`en and sonic Mach numbers, are consistent within a factor 1 to
2 with the values of the same turbulent regimes estimated from the analysis of
Zeeman measurements data provided by Crutcher (1999). Constraints on the values
of the inclination angle of the mean magnetic field with respect to the LOS are
also given. The values obtained from the comparison of the simulations with the
SCUPOL data are consistent with the estimates made by use of two different
observational methods provided by other authors. Our main conclusion is that
simple ideal, isothermal and non-selfgraviting MHD simulations are sufficient
to describe the large scale observed physical properties of the envelopes of
this set of regions.
