Density structure (total hydrogen nuclei number density n _⟨ H ⟩ ) of a T Tauri disk model as function of radial distance from the star r and the relative height z/r. Gas in thermal balance. The red dashed line shows the temperature boundary where T_g = 1000   K. The regions under consideration for this paper are shown as black ovals (P1, and P2 for benchmarking). This figure is taken from the ProDiMo simulation (Woitke et al. 2009).