Pressure temperature profiles at the substellar point of the four planets studied here. The short dash portion of the profiles are the 1.4 μm photospheric pressures. The long-dash portions represent what the photospheric pressures would be if water dissociation were not taken into account. The background and the black contour lines show the water abundance for a solar composition gas as a function of pressure and temperature. The dashed-dot brown contour lines are the contour lines of the ratio between the opacities of molecules (mainly H₂ O and TiO) and the bound-free opacity of H⁻ calculated at1.25 μm. At higher temperatures and lower pressures than the line labeled “1”, H⁻ is an important opacity source in the atmosphere.