Vasavada, A. R., Porco, C. C., Baines, K. H., del Genio, A. D., Ingersoll, A. P., West, R. A., Horst, S. M. (2005). "New Views of Saturn's Dynamic Atmosphere from Cassini ISS and VIMS." Eos Trans. AGU 86(52), Fall Meet. Suppl., Abstract P23D-07 I.


Cassini's Imaging Science Subsystem (ISS) and Visual and Infrared Mapping Spectrometer (VIMS) have fundamentally improved our understanding of Saturn's atmospheric dynamics since the spacecraft approached Saturn in early 2004. Imaging by the ISS at visible and near-infrared wavelengths allows simultaneous studies of winds and vertically distinct clouds and hazes. Feature tracking on deeper-sounding (near-infrared continuum) images results in zonal wind speeds that differ only slightly from those measured by Voyager. Tracking on methane absorption-band images, which emphasize higher-altitude features, reveals vertical wind shear in the equatorial region. The eddy momentum flux has been measured and will be compared with recent ISS results from Jupiter. The morphology, location, behavior, and life cycle of atmospheric vortices have been documented on 8 months of regularly acquired images. Convective storms are observed to occur near 35S and are correlated with Saturn Electrostatic Discharge events. VIMS has produced the first measurements of zonal winds at the two-bar level, using 5.1-micron images, where upwelling thermal radiation dominates over reflected sunlight. Overlying clouds attenuate this radiation, allowing the clouds to be mapped on both the day and night sides. Tracking these backlit clouds enables the determination of winds at a relatively deep level in the atmosphere near the two-bar level near where relatively large particles (>~5 micron radius) reside within a major cloud layer, possibly composed of ammonium hydrosulfide. Comparison of these winds with those determined by tracking sunlit cloud features enables the estimation of vertical wind shears.