 Semi-grey irradiated atmosphere

A semi-grey irradiated atmosphere uses separate averaged opacities for incoming stellar light and outgoing planetary thermal radiation. Their ratio $\gamma ={\kappa }_{\mathrm{vis}}/{\kappa }_{\mathrm{IR}}$ compares where the two energy streams interact with matter. Large visible opacity relative to infrared opacity deposits stellar heat at a relatively small thermal optical depth; sufficiently strong high-altitude heating can produce an atmospheric thermal inversion.^[ref]

The model connects irradiation temperature, internal effective temperature of a planet and heating depth to an atmospheric pressure-temperature profile. It is useful for interpreting broad thermal structure, but averaging each band suppresses spectral windows and molecular lines that matter in detailed atmospheric retrieval.