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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.05.018 Byline: E. Lellouch (a), B. Bezard (a), D.F. Strobel (b), G.L. Bjoraker (c), F.M. Flasar (c), P.N. Romani (c) Keywords: Jupiter; atmosphere; Atmospheres; dynamics; Atmospheres; composition Abstract: Observations of Jupiter by Cassini/CIRS, acquired during the December 2000 flyby, provide the latitudinal distribution of HCN and CO.sub.2 in Jupiter's stratosphere with unprecedented spatial resolution and coverage. Following up on a preliminary study by Kunde et al. [Kunde, V.G., and 41 colleagues, 2004. Science 305, 1582-1587], the analysis of these observations leads to two unexpected results (i) the total HCN mass in Jupiter's stratosphere in 2000 was (6.0[+ or -]1.5)x10.sup.13g, i.e., at least three times larger than measured immediately after the Shoemaker-Levy 9 (SL9) impacts in July 1994 and (ii) the latitudinal distributions of HCN and CO.sub.2 are strikingly different: while HCN exhibits a maximum at 45[degrees] S and a sharp decrease towards high Southern latitudes, the CO.sub.2 column densities peak over the South Pole. The total CO.sub.2 mass is (2.9[+ or -]1.2)x10.sup.13g. A possible cause for the HCN mass increase is its production from the photolysis of NH.sub.3, although a problem remains because, while millimeter-wave observations clearly indicate that HCN is currently restricted to submillibar ([approximately equal to]0.3mbar) levels, immediate post-impact infrared observations have suggested that most of the ammonia was present in the lower stratosphere near 20 mbar. HCN appears to be a good atmospheric tracer, with negligible chemical losses. Based on 1-dimensional (latitude) transport models, the HCN distribution is best interpreted as resulting from the combination of a sharp decrease (over an order of magnitude in K.sub.yy) of wave-induced eddy mixing poleward of 40[degrees] and an equatorward transport with [approximately equal to]7cms.sup.-1 velocity. The CO.sub.2 distribution was investigated by coupling the transport model with an elementary chemical model, in which CO.sub.2 is produced from the conversion of water originating either from SL9 or from auroral input. The auroral source does not appear adequate to reproduce the CO.sub.2 peak over the South Pole, as required fluxes are unrealistically high and the shape of the CO.sub.2 bulge is not properly matched. In contrast, the CO.sub.2 distribution can be fit by invoking poleward transport with a [approximately equal to]30cms.sup.-1 velocity and vigorous eddy mixing (K.sub.yy=2x10.sup.11cm.sup.2s.sup.-1). While the vertical distribution of CO.sub.2 is not measured, the combined HCN and CO.sub.2 results imply that the two species reside at different stratospheric levels. Comparing with the circulation regimes predicted by earlier radiative-dynamical models of Jupiter's stratosphere, and with inferences from the ethane and acetylene stratospheric latitudinal distribution, we suggest that CO.sub.2 lies in the middle stratosphere near or below the 5-mbar level. Author Affiliation: (a) Observatoire de Paris, F-92195 Meudon, France (b) The Johns Hopkins University, Baltimore, MD 21218, USA (c) NASA/GFSC, Code 693, Greenbelt, MD 20771, USA Article History: Received 14 November 2005; Revised 11 May 2006

Unlike other moons in the solar system, Titan has a substantial atmosphere and offers an interesting comparison with Earth and the other planets. Its pressure at the surface is 1.5 [...], Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15°S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan. Above the south pole, temperatures in the stratosphere are 4 to 5 kelvin cooler than at the equator. The stratospheric mole fractions of methane and carbon monoxide are (1.6 ± 0.5) x [10.sup.-2] and (4.5 ± 1.5) x [10.sup.-5] respectively.

Cassini observations of Saturn provide a detailed comparison with Jupiter, successfully studied by Galileo, which will sharpen our ideas about the formation of planetary systems. Each giant, fluid planet has [...], Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites.

Jupiter serves as an analog for the numerous extrasolar planets that have been detected; the formation and evolution of these are not well understood. The primary paradigm is Jupiter, which [...], The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of acetylene and ethane, the latter a tracer of atmospheric motion; observations of unexpected spatial distributions of carbon dioxide and hydrogen cyanide, both considered to be products of comet Shoemaker-Levy 9 impacts; characterization of the morphology of the auroral infrared hot spot acetylene emission; and a new evaluation of the energetics of the northern auroral infrared hot spot.

The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of ~140?m?s-1, whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere. [ABSTRACT FROM AUTHOR]