 Atmospheric pressure-temperature profile

An atmospheric pressure-temperature profile specifies temperature as a function of pressure through an exoplanet atmosphere. Pressure normally increases inward under hydrostatic equilibrium, so it is a useful vertical coordinate even when the absolute altitude is uncertain. In a radiative equilibrium region, heating and cooling by radiation determine the profile; where that profile would be unstable, convection can carry energy and bring the gradient close to an adiabatic temperature gradient.

The profile explains why a molecular band can appear in absorption or as emission lines. Greater opacity makes the emerging light sample a higher layer. If that layer is colder, the band is dimmer; an atmospheric thermal inversion can reverse this behaviour. An atmospheric retrieval therefore needs both abundances and the profile, rather than identifying composition from band depth alone.