36th DPS Meeting, 8-12 November 2004
Session 30 Jupiter and Saturn: Composition, Structure, Dynamics
Oral, Thursday, November 11, 2004, 1:45-4:15pm, Clark

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[30.07] Saturn's Atmosphere: An Infrared Assessment Using Cassini CIRS and Earth-Based Observations

G. Orton, B. Fisher, P. Yanamandra-Fisher, M. Ressler (Jet Propulsion Laboratory / Caltech), R. Campbell, M. Kassis (W. M. Keck Observatory), J. Hora, L. Deutsch (Harvard / Ctr. for Astrophys.), R. Achterberg (Science Systems and Applications, Inc.), B. Conrath (Cornell Univ.), A. Swenson (Caltech), J. Katz, A. Winfield (Columbia Univ.)

The Cassini Composite Infrared Spectrometer (CIRS) investigation has begun taking the first of thousands of spectra of Saturn's atmosphere between ~20 and 1400 cm-1 (7 and ~50 microns). The spectra are sensitive to Saturn's temperature structure between 1 and 600 mbars pressure. The CIRS observations are complemented by a dedicated program of supporting ground-based imaging between 7.8 and 24 microns (~400-1300 cm-1), mostly from NASA's Infrared Telescope Facility but also including data from the W. M. Keck I and the Gemini/North Observatories. These build on an existing set of observations which began more than 20 years ago. CIRS data and recent images reveal a complex temperature field, with several remarkable features. One is the presence of thermal waves at mid-southern latitudes which may be a manifestation of slowly-moving thermal features, as in Jupiter. Another is the series of bright and dark axisymmetric bands at midlatitudes from 45 to 75 degrees S latitude. The antarctic region is very warm from about 75 degrees S to the south pole. The most striking aspect of Saturn's upper tropospheric and stratospheric temperature fields is a hot region within 2 degrees latitude of the south pole. The south polar feature is thus a warm (and double) polar vortex. Just as for Jupiter's polar vortex boundaries, temperature differences do NOT appear to dissipate with altitude. The CIRS investigation will determine whether Saturn's arctic region has developed a cold polar vortex through its long years of darkness in Saturn's northern winter.

Funding for this work was provided by NASA. A. Swenson and A. Winfield were Summer Undergraduate Research Fellows at JPL. J. Katz was an Undergraduate Student Research Program participant at JPL.

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Bulletin of the American Astronomical Society, 36 #4
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