Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p11c1287k&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P11C-1287
Physics
0321 Cloud/Radiation Interaction, 3311 Clouds And Aerosols, 6275 Saturn
Scientific paper
We present the first visible-to-near-infrared analysis of two new distinct types of bright and dark clouds in Saturn's thunderstorm region near 35 degrees S. latitude (planetocentric) between 290 and 330 degrees W. longitude as observed by the Visual-Infrared Mapping Spectrometer (VIMS) onboard the Cassini-Huygens orbiter on February 9, 2008. Specifically, we have analyzed the 0.35 - 3.1-micron spectra of these clouds to constrain their composition and structure. Our initial analysis indicates that the spectroscopic character of these spectrally bright clouds are consistent with the presence of ammonia ice absorption, supporting the possibility of ammonia ice particles in Saturnian clouds suggested previously by high-resolution spectroscopic ground-based observations (Kim et al., 2006, Icarus 185, 476-486). Specifically, these clouds are depleted in 2.73-micron reflectivity, similar to Jupiter's spectroscopically- identifiable clouds (Baines et al, 2002, Icarus 159, 74-94). The much darker clouds located downstream of the lightning site have unusually low albedo at all near-continuum wavelengths. The location of the dark clouds downstream in the zonal winds indicates that these are older features, suggesting that they are delayed convective upwellings of thermo-chemically generated material from deeper depths We present the characteristics as a function of wavelength on these both types of thunderstorm related clouds - single scattering albedos, cloud top altitudes, mean particle sizes, refractive indices, and constraints on the composition of both cloud types. We also present the effective pressure (depth) of sunlight penetration into the atmosphere of Saturn as a function of wavelength from 0.3 microns to 4.5 microns, calculated with the recent low-temperature methane absorption coefficients of Irwin et al (Icarus 181, 309-319, 2006). These show that most of the hazes and clouds of Saturn probed by reflected sunlight in the visible and near-infrared are limited to above the 1-bar level.
Baines Kevin Hays
Brown Harvey R.
Buratti Bonnie Jean
Cassini Science Team
Clark Roger Nelson
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