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F. M. Flasar, A. A. Simon-Miller (GSFC), R. K. Achterberg (SSAI), B. J. Conrath, P. J. Gierasch (Cornell), V. G. Kunde, C. Nixon (UMD), D. E. Jennings, P. N. Romani (GSFC), P. Irwin (Oxford U), B. Bezard (DESPA), R. Carlson (SSAI), Cassini CIRS Investigation Team
During the 140-RJ Cassini swingby of Jupiter in December 2000, the Composite Infrared Spectrometer (CIRS) acquired global maps of Jupiter with a spatial resolution up to 2.5o of latitude at the sub-spacecraft point at middle-infrared wavelengths (600-1400 cm-1). Temperatures retrieved from this spectral range are in the upper troposphere and tropopause region (50-400 mbar), and in the middle and upper stratosphere (0.8-10 mbar). Zonally averaged temperatures imply a mean zonal wind that does not have a simple structure: the winds decay with altitude near the tropopause, but higher up they can either decay to a state of no relative motion or build up again, implying a complex spatial distribution of momentum forcing. Zonal mean temperatures at low latitudes exhibit an interesting behavior. Near 100 mbar and 1 mbar, equatorial temperatures are several kelvin cooler than those 10-15o N or S. However, at 5-20 mbar the equatorial temperatures are ~5 K warmer. At the tropopause, the equatorial temperature minimum is much more pronounced than observed at the time of Voyager. While a number of mechanisms could account for this spatial behavior, it is likely related to the temporal variation in the equatorial stratospheric temperatures that have been reported from ground-based observations. The global maps obtained show the two auroral hot spots at high northern and southern latitudes. Curiously, these spots appear cooler than their surroundings at the 4-mbar level, perhaps attributable to adiabatic cooling associated with local upwelling. The maps also show a wealth of distinct zonal structure at other latitudes. Much of this appears quasi-stationary, but several westward-propagating features are seen in the stratosphere.