Thunderstorm-Related Clouds and Atmospheric Structures of Saturn Observed by Cassini/VIMS

Details Thunderstorm-Related Clouds and Atmospheric Structures of Saturn Observed by Cassini/VIMS Thunderstorm-Related Clouds and Atmospheric Structures of Saturn Observed by Cassini/VIMS

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.4109k&link_type=abstract

American Astronomical Society, DPS meeting #40, #41.09; Bulletin of the American Astronomical Society, Vol. 40, p.471

Astronomy and Astrophysics

Astronomy

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. The brighter clouds are located at the predicted longitude of maximum lightning activity as determined by the RPWS measurements of Saturn Electrostatic Discharges (SEDs). 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). Specifically, these clouds are depleted in 2.73-micron reflectivity, similar to Jupiter's spectroscopically-identifiable clouds (Baines et al, 2002). 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 of both types of thunderstorm-associated clouds - single scattering albedos, cloud top altitudes, mean particle sizes, 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 (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.

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