Radiative equilibrium model of Titan's atmosphere

A simple global radiative equilibrium model is developed for Titan. It is restricted to the two-stream approximation, is vertically homogeneous in its scattering properties, and is spectrally divided into one thermal and two solar channels. A partially absorbing “violet” channel is responsible for heating in the stratosphere, while a conservatively scattering “red” channel permits heating at the surface. The optical thickness of the atmosphere in the red is 1 < τ₁^r < 3. Between 13 and 33% of the total incident solar radiation is absorbed at the planetary surface. The ratio of violet to thermal infrared absorption cross sections is between 30 and 60 in the stratosphere, leading to the large temperature inversion observed there. The observed and theoretically computed tropopause temperatures are 72 and 69°K, respectively, while their corresponding thermal optical depths are, respectively, ～0.1 and ～0.07. The spectrally integrated mass absorption coefficient at thermal wavelengths is approximately constant throughout the stratosphere and roughly linear with pressure in the troposphere. This in turn implies the presence of a uniformly mixed aerosol in the stratosphere, and suggests pressure-induced absorption by gaseous N₂CH₄H₂ in the troposphere. In addition there appear to be two regions of enhanced opacity near 30 and 500 mbar which may be due to C₂H₂C₂H₆C₃H₈ and CH₄ condensation clouds, respectively.