  Lindal et al. (1987, J. Geophys. Res. 92, 14987-15001) presented a range of
temperature and CH4 profiles for Uranus that were consistent with 1986 Voyager
radio occultation measurements. A localized refractivity slope variation near
1.2 bars was interpreted to be the result of a condensed CH4 cloud layer.
However, models fit to near-IR spectra found particle concentrations in the
1.5-3 bar range (Sromovsky et al. 2006, Icarus 182, 577-593, Sromovsky and Fry
2008, Icarus 193, 211-229, Irwin et al. 2010, Icarus 208, 913-926), and a
recent analysis of STIS spectra argued that aerosol particles formed diffusely
distributed hazes, with no compact condensation layer (Karkoschka and Tomasko
2009, Icarus 202, 287-309). Trying to reconcile these results, we reanalyzed
the occultation observations with a He volume mixing ratio reduced from 0.15 to
0.116, which is near the edge of the 0.033 range given by Conrath et al. (1987,
J. Geophys. Res., 15003-10). This allowed us to obtain saturated CH4 mixing
ratios within the putative cloud layer and to reach above-cloud and deep CH4
mixing ratios compatible with STIS spectral constraints. Using a 5-layer
vertical aerosol model with two compact cloud layers in the 1-3 bar region, we
find that the best fit pressure for the upper layer is virtually identical to
the pressure range inferred from the occultation analysis for a methane mixing
ratio near 4% at 5 deg S, arguing that Uranus does indeed have a compact
methane cloud layer. While our cloud model can fit the latitudinal variations
in spectra between 30 deg S and 20 deg N using the same temperature and CH4
profiles, closer to the pole, the model requires the introduction of an
increasingly strong upper tropospheric depletion of CH4 at increased latitudes,
in rough agreement with the trend identified by Karkoschka and Tomasko (2009,
Icarus 202, 287-309).
