Thermal structure of Uranus' atmosphere

Application of a radiative-convective equilibrium model to the thermal stru cture of Uranus' atmosphere evaluates the role of hazes in the planet's str atospheric energy budget and places a lower limit on the internal energy fl ux. The model is constrained by Voyager and post-Voyager observations of th e vertical aerosol and radiatively active gas profiles. Our baseline model generally reproduces the observed tropospheric and stratospheric temperatur e profile. However, as in past studies, the model stratosphere from about 1 0(-3) to 10(-1) bar is too cold. We find that the observed stratospheric ha zes do not warm this region appreciably and that any postulated hazes capab le of warming the stratosphere sufficiently are inconsistent with Voyager a nd ground-based constraints, We explore the roles played by the stratospher ic methane abundance, the H-2 pressure-induced opacity, photochemical hazes , and C2H2 and C2H6 in controlling the temperature structure in this region . Assuming a vertical methane abundance profile consistent with that found by the Voyager WS occultation observations, the model upper stratosphere, f rom 10 to 100 mu bar, is also too cold. Radiation in the 7.8-mu m band from a small abundance of hot methane in the lower thermosphere absorbed in thi s region can warm the atmosphere and bring models into closer agreement wit h observations. Finally, we find that internal heat fluxes less than or sim ilar to 60 erg cm(-2) sec(-1) are inconsistent with the observed tropospher ic temperature profile. (C) 1999 Academic Press.