Vertical temperature gradients on Uranus: Implications for layered convection

Abstract

Analyses of Voyager infrared spectroscopy and radio occultation measurements confirm ground‐based observations that the deep lapse rate of Uranus exceeds that for an adiabat of molecular hydrogen in thermodynamic equilibrium. However, in approximately the same region of the atmosphere, Voyager infrared and ground‐based observations also indicate that the ratio of ortho to para hydrogen is near the equilibrium value. These two sets of observations can be reconciled by postulating the existence of rapid convective overturning within layers which are thin in comparison to a pressure scale height. Two forms of layered convection are examined. In one case, deposition of kinetic energy results in thin, rapidly overturning layers. Possible kinetic energy sources include breaking waves and local instabilities. In the second case considered, molecular weight discontinuities due to methane stratification stabilize the interfaces of thin layers. It is argued that both forms may be important in the convective portion of the Uranus atmosphere.