Possible cloud structure of Uranus and Jupiter from thermochemical models and observations

The Equilibrium Cloud Condensation Model (ECCM) predicts a multi-layer cloud structure in the troposphere on the giant planets (Weidenschilling and Lewis, Icarus, 20, 1973; Atreya and Romani, Planetary Meteorology, 1985). Here we include the effect of a heavier molecular weight of the condensate compared to that of atmosphere, which impacts the atmospheric lapse rate. We further include the effect of precipitation, which can reduce the aerosol concentration by several orders of magnitude, in the absence of dynamics or local meteorology. We test the model by applying it to Earth. This gives us some confidence in the predictions for the giant planets. Radio observations have provided valuable insight into Uranus atmosphere since the early 1980's (Briggs and Andrew, Icarus, 41, 1980, and de Pater and Gulkis, Icarus, 71, 1988). Here, we employ the VLA data on Uranus obtained since 2003 (Hofstadter and Butler, Icarus, 165, 2003, and Hofstadter and Butler in preparation) as constraints, and also take advantage of ground based data in the visible and IR wavelengths (Baines et al., Icarus, 114, 1995). The latter observations of albedo point to an optically thick cloud top in the 3.1 (+1.1, -0.2) bar region for Uranus; however, there are some uncertainties in the measurements due to the methane absorption coefficient. These uncertainties resulted in the proposal of a two-cloud solution at Uranus with significant cloud layers at 2 and 6 bars (Sromovsky et al., Icarus, 146, 2006). Using a combination of data and models we seek to determine the possibility of solutions for both the one and two cloud solution at Uranus, by including phosphine and hydrogen sulfide aerosol layers.