A Comparison of Cassini CIRS Measurements of Saturn's Troposphere with Ground-based Observations

Ground-based and Cassini/VIMS images of Saturn at 5.1 microns exhibit spectacular spatial structure which we attribute to variations in the opacity of the NH4SH cloud near the 3-bar level. If this cloud structure is due to upwelling in zones and downwelling in belts as on Jupiter, there should also be spatial structure at the NH3 cloud level. Cassini/CIRS observations of Saturn between 20 and 100 cm-1 (100 - 500 microns) sound levels in the troposphere between 0.5 and 1.1 bars. CIRS far-IR spectra are sensitive to temperature, NH3, PH3, and cloud opacity. Observations at 15 cm-1 resolution were used to investigate the latitudinal variation of NH3 cloud opacity while 0.5 cm-1 spectra were used to retrieve NH3 and PH3 at selected latitudes. Preliminary results suggest some correlation with 5-micron data. Saturn is brighter at 53S than at 15S latitude in CIRS spectra longward of 100 microns. Models of Saturn require more continuum opacity at 10-15S than elsewhere in the Southern hemisphere at the levels predicted for both NH3 and NH4SH clouds.