DPS 35th Meeting, 1-6 September 2003
Session 50. Outer Planets/Gas Giants III
Oral, Chairs: G. Orton and K. A. Rages, Saturday, September 6, 2003, 3:30-5:40pm, DeAnza I-II

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[50.04] Pre-Cassini Infrared Characterization of Saturn's Atmosphere

G. Orton, B. Fisher, P. Yanamandra-Fisher, K. Baines, M. Ressler (JPL/Caltech), B. Beach-Kimball (Wesleyan U.), B. Jackson (Georgia Inst. Tech.), D. Gezari (Goddard Space Flight Ctr.), F. Varosi (U. florida)

We report 23 years of infrared remote sensing observations of Saturn, primarily at the NASA Infrared Telescope Facility to establish a long-term baseline against which Cassini remote-sensing observations can be compared. Cloud structure is constrained by near-infrared reflected sunlight, where images reveal stratospheric haze between -11 and +18 degrees planetocentric latitude, but not at the poles (unlike Jupiter). Thermal emission at 5.2 microns senses clouds near 2-3 bars which are strikingly inhomogeneous spatially, with large zonal variations near the equator and 45 degrees S. Stratospheric temperatures near 10 mbar are sensed by 7.85-micron CH4 emission and (with C2H6 abundance variations) by 12.2-micron C2H6 emission. Tropospheric temperatures near 100-400 mbar are sensed by H2 collision-induced emission between 17 and 24 microns. Strong seasonal forcing of stratospheric temperatures is evident, with temperatures tracking the insolation variations with a several-year delay. A target-of-opportunity observation on a Keck engineering night in 1998 shows a strong peak of stratospheric temperature (or CH2H6 abundance) poleward of 81degrees S latitude. Just as for Jupiter, meridional variations of stratospheric and tropospheric temperatures are not correlated with one another. Planetary-scale zonal waves as large as 1 Kelvin amplitude are seen in the stratospheric temperature field, with some evidence for even larger-amplitude waves in the troposphere. Cassini may detect an arctic region of depressed temperatures with a non-uniform southern boundary, if a polar vortex, similar to those in Titan and Jupiter, is driven by the seasonal loss of insolation north of its arctic circle.

This work was supported by funds from NASA to JPL and GSFC. Brett Beach-Kimball was supported by the Undergraduate Student Researcher Program (USRP); Brian Jackson was supported by JPL as a Caltech Summer Undergraduate Research Fellow (SURF).

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.