Histogram shape parameter ξ (Eqs. (4) and (5)) calculated for the different N_H bins in each region. Top: relative orientation in synthetic observations of simulations with super-Alfvénic (blue), Alfvénic (green), and sub-Alfvénic (red) turbulence, as detailed in Soler et al. (2013). Middle: relative orientation in the regions selected from the Planck all-sky observations, from Fig. 7. The blue data points correspond to the lowest N_H regions (CrA and the test regions in Fig. 8, ChamSouth and ChamEast) and the orange correspond to the rest of the clouds. Bottom: comparison between the trends in the synthetic observations (in colours) and the regions studied (grey). The observed smooth transition from mostly parallel (ξ> 0) to perpendicular (ξ< 0) is similar to the transition in the simulations for which the turbulence is Alfvénic or sub-Alfvéic.