In the opaque (optically thick) region of the atmosphere, (low altitudes), the equilibrium temperature is simply the one for which the atmosphere is in thermodynamic equilibrium with the incident solar flux. The atmosphere will assume an adiabatic profile such that

Above this level, for , the atmosphere is transparent (optically thin), so it does not interact with incident radiation. Its kinetic temperature must therefore simply represent some average between below and the T = 0 of space below. This average, denoted for stratospheric temperature, is conventionally found according to

so