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The temperatures of giant-planet upper atmospheres at mid- to low latitudes are measured to be hundreds of degrees warmer than simulations based on solar heating alone can explain (1-4). Modelling studies that focus on additional sources of heating have been unable to resolve this major discrepancy. Equatorward transport of energy from the hot auroral regions was expected to heat the low latitudes, but models have demonstrated that auroral energy is trapped at high latitudes, a consequence of the strong Coriolis forces on rapidly rotating planets (3-5). Wave heating, driven from below, represents another potential source of upper-atmospheric heating, though initial calculations have proven inconclusive for Jupiter, largely owing to a lack of observational constraints on wave parameters (6,7). Here we report that the upper atmosphere above Jupiter's Great Red Spot-the largest storm in the Solar System-is hundreds of degrees hotter than anywhere else on the planet. This hotspot, by process of elimination, must be heated from below, and this detection is therefore strong evidence for coupling between Jupiter's lower and upper atmospheres, probably the result of upwardly propagating acoustic or gravity waves., On 4 December 2012 (Coordinated Universal Time, UTC) we observed Jupiter for 9 h using the SpeX spectrometer (8) on the NASA Infrared Telescope Facility. The spectrometer slit was aligned [...]

With the exception of the Great Red Spot, Jupiter's long-lived vortices are not isolated, but occur in east west rows. Each row is centered about a westward-going jet stream with anticyclones on the poleward side and cyclones on the equatorial. Vortices are staggered so that like-signed vortices are never longitudinally adjacent. These double rows of vortices, called here Jovian vortex streets (JVSs) are robust. Calculations with no forcing and no dissipation (i.e., Hamiltonian dynamics) allow a continuum of JVS solutions, so they cannot be used to determine the physics that selects the observed values of the areas, circulations, and locations of Jupiter's vortices. Constraints imposed by stability put few bounds on these values. When small amounts of dissipation and forcing are added to the governing equations, there is no longer a continuum of solutions: an initial JVS that was a solution of the Hamiltonian equations is now out of equilibrium and evolves to an attractor. For fixed forcing, all initial JVS evolve to the same attractor, so that the area of the vortices in the late-time JVS is selected uniquely as is the separation width in latitude between the row of cyclones and row of anticyclones. The separation width of the attracting JVS is nearly independent of the forcing, but the areas of the vortices in the attracting JVS depend strongly on the strength of the forcing, which is a measure of the ambient Jovian turbulence. Results are compared with observations.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.09.022 Byline: Robert R. Howell (a), Rosaly M.C. Lopes (b) Keywords: Io; Volcanism; Infrared observations; Jupiter; satellites; Satellites; surfaces; Geological processes Abstract: Loki is the largest patera and the most energetic hotspot on Jupiter's moon Io, in turn the most volcanically active body in the Solar System, but the nature of the activity remains enigmatic. We present detailed analysis of Galileo Near-Infrared Mapping Spectrometer (NIMS) and PhotoPolarimeter/Radiometer (PPR) observations covering the 1.5-100 [mu]m wavelength range during the I24, I27, and I32 flybys. The general pattern of activity during these flybys is consistent with previously proposed models of a resurfacing wave periodically crossing a silicate lava lake. In particular our analysis of the I32 NIMS observations shows, over much of the observed patera, surface temperatures and implied ages closely matching those expected for a wave advancing counterclockwise at 0.94-1.38 km/day. The age pattern is different than other published analyses which do not show as clearly this azimuthal pattern. Our analysis also shows two additional distinctly different patera surfaces. The first is located along the inner and outer margins where components with a 3.00-4.70-[mu]m color temperature of 425 K exist. The second is located at the southwestern margin where components with a 550-K color temperature exist. Although the high temperatures could be caused by disruption of a lava lake crust, some additional mechanism is required to explain why the southwest margin is different from the inner or outer ones. Finally, analysis of the temperature profiles across the patera reveal a smoothness that is difficult to explain by simple lava cooling models. Paradoxically, at a subpixel level, wide temperature distributions exist which may be difficult to explain by just the presence of hot cracks in the lava crust. The resurfacing wave and lava cooling models explain well the overall characteristics of the observations. However, additional physical processes, perhaps involving heat transport by volatiles, are needed to explain the more subtle features. Author Affiliation: (a) Department of Geology & Geophysics, University of Wyoming, Laramie, WY 82071, USA (b) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA Article History: Received 18 February 2006; Revised 17 September 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.08.009 Byline: Amy A. Simon-Miller (a), Bradley W. Poston (b), Glenn S. Orton (c), Brendan Fisher (c) Keywords: Jupiter; atmosphere; Atmospheres; dynamics; Infrared observations Abstract: Jupiter's equatorial atmosphere, much like the Earth's, is known to show quasi-periodic variations in temperature, particularly in the stratosphere, but variations in other jovian atmospheric tracers have not been studied for any correlations to these oscillations. Data taken at NASA's Infrared Telescope Facility (IRTF) from 1979 to 2000 were used to obtain temperatures at two levels in the atmosphere, corresponding to the upper troposphere (250 mbar) and to the stratosphere (20 mbar). We find that the data show periodic signals at latitudes corresponding to the troposphere zonal wind jets, with periods ranging from 4.4 (stratosphere, 95% confidence at 4[degrees] S planetographic latitude) to 7.7 years (troposphere, 97% confidence at 6[degrees] N). We also discuss evidence that at some latitudes the troposphere temperature variations are out of phase from the stratosphere variations, even where no periodicity is evident. Hubble Space Telescope images were used, in conjunction with Voyager and Cassini data, to track small changes in the troposphere zonal winds from 20[degrees] N to 20[degrees] S latitude over the 1994-2000 time period. Oscillations with a period of 4.5 years are found near 7[degrees]-8[degrees] S, with 80-85% significance. Further, the strongest evidence for a QQO-induced tropospheric wind change tied to stratospheric temperature change occurs near these latitudes, though tropospheric temperatures show little periodicity here. Comparison of thermal winds and measured zonal winds for three dates indicate that cloud features at other latitudes are likely tracked at pressures that can vary by up to a few hundred millibar, but the cloud altitude change required is too large to explain the wind changes measured at 7[degrees] S. Author Affiliation: (a) NASA's Goddard Space Flight Center, Code 693.0, Greenbelt, MD 20771, USA (b) University of Maryland College Park, 1208B Cambridge Hall, College Park, MD 20742, USA (c) Jet Propulsion Laboratory, 4800 Oak Grove Road, M/S 169-237, Pasadena, CA 91109, USA Article History: Received 24 February 2006; Revised 3 August 2006

Jupiter's equatorial atmosphere, much like the Earth's, is known to show quasi-periodic variations in temperature, particularly in the stratosphere, but variations in other jovian atmospheric tracers have not been studied for any correlations to these oscillations. Data taken at NASA's Infrared Telescope Facility (IRTF) from 1979 to 2000 were used to obtain temperatures at two levels in the atmosphere, corresponding to the upper troposphere (250 mbar) and to the stratosphere (20 mbar). We find that the data show periodic signals at latitudes corresponding to the troposphere zonal wind jets, with periods ranging from 4.4 (stratosphere, 95% confidence at 4[degrees] S planetographic latitude) to 7.7 years (troposphere, 97% confidence at 6[degrees] N). We also discuss evidence that at some latitudes the troposphere temperature variations are out of phase from the stratosphere variations, even where no periodicity is evident. Hubble Space Telescope images were used, in conjunction with Voyager and Cassini data, to track small changes in the troposphere zonal winds from 20[degrees] N to 20[degrees] S latitude over the 1994-2000 time period. Oscillations with a period of 4.5 years are found near 7[degrees]-8[degrees] S, with 80-85% significance. Further, the strongest evidence for a QQO-induced tropospheric wind change tied to stratospheric temperature change occurs near these latitudes, though tropospheric temperatures show little periodicity here. Comparison of thermal winds and measured zonal winds for three dates indicate that cloud features at other latitudes are likely tracked at pressures that can vary by up to a few hundred millibar, but the cloud altitude change required is too large to explain the wind changes measured at 7[degrees] S. Keywords: Jupiter, atmosphere; Atmospheres, dynamics; Infrared observations

We present a detailed study of the distribution of key deuterated species (viz., atomic D and HD) and the associated deuterium Lyman-[alpha] airglow in the jovian thermosphere. The reactions that appear to govern the abundances of these deuterated species are used in conjunction with [C.sub.2]-chemistry in a 1-D photochemical-diffusion model. While the D abundance is mainly sensitive to H densities and the vibrational temperature profile, the D vertical distribution also depends on other parameters such as eddy mixing and the uncertain values of some of the reaction rate constants. We consider different scenarios by varying several parameters controlling the D distribution in the thermosphere. A radiative transfer model with coupling of the H and D Lyman-[alpha] lines is employed to obtain line profiles and total intensities at disk center for these scenarios. This allows a comparison of the impact of various parameters on the jovian D Lyman-[alpha] emission. A consequence of these chemical processes in the jovian thermosphere is the formation of C[H.sub.2]D, C[H.sub.3]D, and [C.sub.2][H.sub.5]D, and other deuterated species. We also discuss the source of these deuterated hydrocarbons and their abundance. We find that HD vibrational chemistry impacts D in the thermosphere, C[H.sub.3]D and [C.sub.2] [H.sub.5]D are vibrationally enhanced in the thermosphere, and variations in abundance of C[H.sub.3]D and [C.sub.2][H.sub.5]D in the thermosphere may reflect dynamical activity (i.e., [K.sub.h]) in the jovian upper atmosphere. An observing program dedicated to providing such measurements of these testable phenomena would provide further insight into the synergistic coupling between chemistry, energetics and airglow in the jovian upper atmosphere. Keywords: Jupiter, atmosphere; Photochemistry; Radiative transfer; Abundances, atmospheres

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.02.001 Byline: Frank Postberg (a), Sascha Kempf (a), Ralf Srama (a), Simon F. Green (b), Jon K. Hillier (b), Neil McBride (b), Eberhard Grun (a)(c) Keywords: Jupiter; Interplanetary dust; Io; Volcanism; Satellites; atmospheres Abstract: The Cassini spacecraft encountered Jupiter in late 2000. Within more than 1 AU of the gas giant the Cosmic Dust Analyser onboard the spacecraft recorded the first ever mass spectra of jovian stream particles. To determine the chemical composition of particles, a comprehensive statistical analysis of the dataset was performed. Our results imply that the vast majority (>95%) of the observed stream particles originate from the volcanic active jovian satellite Io from where they are sprinkled out far into the Solar System. Sodium chloride (NaCl) was identified as the major particle constituent, accompanied by sulphurous as well as potassium bearing components. This is in contrast to observations of gas in the ionian atmosphere, its co-rotating plasma torus, and the neutral cloud, where sulphur species are dominant while alkali and chlorine species are only minor components. Io has the largest active volcanoes of the Solar System with plumes reaching heights of more than 400 km above the moons surface. Our in situ measurements indicate that alkaline salt condensation of volcanic gases inside those plumes could be the dominant formation process for particles reaching the ionian exosphere. Author Affiliation: (a) MPI fur Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany (b) Planetary and Space Sciences Research Institute, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK (c) Hawaii Institute of Geophysics and Planetology, University of Hawaii, 1680 East West Road, Honolulu, HI 96822, USA Article History: Received 21 October 2005; Revised 26 January 2006

The Cassini spacecraft encountered Jupiter in late 2000. Within more than I AU of the gas giant the Cosmic Dust Analyser onboard the spacecraft recorded the first ever mass spectra of jovian stream particles. To determine the chemical composition of particles, a comprehensive statistical analysis of the dataset was performed. Our results imply that the vast majority (>95%) of the observed stream particles originate from the volcanic active jovian satellite Io from where they are sprinkled out far into the Solar System. Sodium chloride (NaCl) was identified as the major particle constituent, accompanied by sulphurous as well as potassium bearing components. This is in contrast to observations of gas in the ionian atmosphere, its co-rotating plasma torus, and the neutral cloud, where sulphur species are dominant while alkali and chlorine species are only minor components. Io has the largest active volcanoes of the Solar System with plumes reaching heights of more than 400 km above the moons surface. Our in situ measurements indicate that alkaline salt condensation of volcanic gases inside those plumes could be the dominant formation process for particles reaching the ionian exosphere. Keywords: Jupiter; Interplanetary dust; Io; Volcanism; Satellites, atmospheres

A box model sensitivity analysis was applied to output from a version of the 1-D JPL/Caltech KINETICS photochemistry-transport model of Jupiter's atmosphere. Results quantify the controlling chemical reaction parameters for the variety of observable hydrocarbons, and suggest changes to explore and new observations and rate measurements to pursue. High sensitivities are found to photolysis steps and to several hydrogen atom recombination steps and product branches. Complexity ranges from the relatively simple scheme seen for the methyl radical, to the rich variety of reactions tested by diacetylene. Keywords: Photochemistry; Jupiter, atmosphere: Atmospheres, composition

Retrievals performed on Cassini Composite Infrared Spectrometer data obtained during the distant Jupiter flyby in 2000/2001 have been used to generate global temperature maps of the planet in the troposphere and stratosphere, but to higher latitudes than were shown previously by Flasar et al. [Flasar, F.M., 39 colleagues, 2004a. Nature 427, 132-135, Flasar, F.M., 44 colleagues, 2004b. Space Sci. Rev. 115, 169-297]. Similar retrievals were performed on Voyager 1 IRIS data to provide the first detailed IRIS map of the stratosphere, and high latitudes in the troposphere. Thermal winds were calculated for each data set and show strong vertical shears in the zonal winds at low latitudes, and meridional temperature gradients indicate the presence of circumpolar jets, as well. The temperatures retrieved from the two spacecraft were also compared with yearly ground-based data obtained over the intervening two decades. Tropospheric temperatures reveal gradual changes at low latitudes, with little obvious seasonal or short-term variation [Orton et al., 1994. Science 265, 625-631]. Stratospheric temperatures show much more complicated behavior over short timescales, consistent with quasi-quadrennial oscillations at low latitudes, as suggested in prior analyses of shorter intervals of ground-based data [Orton et al., 1991. Science 252, 537-542; Friedson, A.J., 1999. Icarus 137, 34-55]. A scaling analysis indicates that meridional motions, mechanically forced by wave or eddy convergence, play an important role in modulating the temperatures and winds in the upper troposphere and stratosphere on seasonal and shorter timescales. At latitudes away from the equator, the mechanical forcing can be derived simply from a temporal record of temperature and its vertical derivative. Ground-based observations with improved vertical resolution and/or long-term monitoring from spacecraft are required for this purpose, though the Voyager and Cassini data given indications that the magnitude of the forcing is very small. Keywords: Jupiter, atmosphere; Atmospheres, dynamics; Atmospheres, temperature

Observations suggest that moist convection plays an important role in the large-scale dynamics of Jupiter's and Saturn's atmospheres. Here we use a reduced-gravity quasigeostrophic model, with a parameterization of moist convection that is based on observations, to study the interaction between moist convection and zonal jets on Jupiter and Saturn. Stable jets with approximately the same width and strength as observations are generated in the model. The observed zonal jets violate the barotropic stability criterion but the modeled jets do so only if the flow in the deep underlying layer is westward. The model results suggest that a length scale and a velocity scale associated with moist convection control the width and strength of the jets. The length scale and velocity scale offer a possible explanation of why the jets of Saturn are stronger and wider than those of Jupiter. Keywords: Jupiter, atmosphere; Saturn, atmosphere; Atmospheres, dynamics

It has been claimed [Canup, R.M., Ward, W.R., 2002. Astron. J. 124, 3404-3423; Ward, W.R., 2003. In: AGU, Fall Meeting 2003] that a long-lived minimum mass circumplanetary gas disk is inconsistent with Jupiter's low obliquity. Here we find that while Jupiter's obliquity may constrain its characteristics it does not rule out a long-lived massive (compared to the mass of the Galilean satellites) disk. This is because the argument assumes a Solar System much like that of the present day with the one exception of a circumjovian disk which is then allowed to dissipate on a long timescale ([10.sup.6]-[10.sup.7] yr). Given that the sequence of events in Solar System history that fit known constraints is non-unique, we choose for the sake of clarity of exposition the orbital architecture framework of Tsiganis et al. [Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F., 2005. Nature 435, 459-461], in which Jupiter and Saturn were once in compact, nearly coplanar orbits, and show that in this case Jupiter's low obliquity is consistent with the SEMM (solids-enhanced minimum mass) satellite formation model of Mosqueira and Estrada [Mosqueira, I., Estrada, P.R., 2003a. Icarus 163, 198-231; Mosqueira, I., Estrada, P.R., 2003b. Icarus 163, 232-255]. We suggest that a low inclination starting condition may apply, but stress that our SEMM satellite formation model could be compatible with Jupiter's obliquity even for mutually inclined giant planets. Keywords: Jupiter; Satellites of Jupiter; Rotational dynamics; Obliquity

We analyze the thermal infrared spectra of Jupiter obtained by the Cassini-CIRS instrument during the 2000 flyby to infer temperature and cloud density in the jovian stratosphere and upper troposphere. We use an inversion technique to derive zonal mean vertical profiles of cloud absorption coefficient and optical thickness from a narrow spectral window centered at 1392 [cm.sup.-1] (7.18 [micro]m). At this wavenumber atmospheric absorption due to ammonia gas is very weak and uncertainties in the ammonia abundance do not impact the cloud retrieval results. For cloud-free conditions the atmospheric transmission is limited by the absorption of molecular hydrogen and methane. The gaseous optical depth of the atmosphere is of order unity at about 1200 mbar. This allows us to probe the structure of the atmosphere through a layer where ammonia cloud formation is expected. The results are presented as height vs latitude cross-sections of the zonal mean cloud optical depth and cloud absorption coefficient. The cloud optical depth and the cloud base pressure exhibit a significant variability with latitude. In regions with thin cloud cover (cloud optical depth less than 2), the cloud absorption coefficient peaks at 1.1 [+ or -] 0.05 bar, whereas in regions with thick clouds the peak cloud absorption coefficient occurs in the vicinity of 900 [+ or -] 50 mbar. If the cloud optical depth is too large the location of the cloud peak cannot be identified. Based on theoretical expectations for the ammonia condensation pressure we conclude that the detected clouds are probably a system of two different cloud layers: a top ammonia ice layer at about 900 mbar covering only limited latitudes and a second, deeper layer at 1100 mbar, possibly made of ammonium hydrosulfide. Keywords: Jupiter; Jupiter, atmosphere; Atmospheres, structure

Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the jovian system is a source of X-rays with a rich and complicated structure. The planet's polar auroral zones and its disk are both powerful sources of X-ray emission. Chandra observations revealed X-ray emission from the Io plasma torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from the moons is due to bombardment of their surfaces by highly energetic magnetospheric protons, and oxygen and sulfur ions. These ions excite atoms in their surfaces leading to fluorescent X-ray emission lines. These lines are produced against an intense background continuum, including bremsstrahlung radiation from surface interactions of primary magnetospheric and secondary electrons. Although the X-ray emission from the Galilean moons is faint when observed from Earth orbit, an imaging X-ray spectrometer in orbit around one or more of these moons, operating from 200 eV to 8 keV with 150 eV energy resolution, would provide a detailed mapping of the elemental composition in their surfaces. Surface resolution of 40 m for small features could be achieved in a 100-km orbit around one moon while also remotely imaging surfaces of other moons and Jupiter's upper atmosphere at maximum regional resolutions of hundreds of kilometers. Due to its relatively more benign magnetospheric radiation environment, its intrinsic interest as the largest moon in the Solar System, and its mini-magnetosphere, Ganymede would be the ideal orbital location for long-term observational studies of the jovian system. Here we describe the physical processes leading to X-ray emission from the surfaces of Jupiter's moons and the properties required for the technique of imaging X-ray spectroscopy to map the elemental composition of their surfaces, as well as studies of the X-ray emission from the planet's aurora and disk and from the Io plasma torus. Keywords: Instrumentation; Experimental techniques; Jupiter, magnetosphere; Io; Europa; Ganymede; Callisto; Aurorae; Abundances; Impact processes

The intensities and distribution of > 1 MeV electrons in Jupiter's mid-magnetosphere have been characterized using the observations of the Galileo Energetic Particle Detector (EPD) instrument. Because of the more than 6 years of observation made by the EPD instrument in this intense radiation environment, and the inherent difficulties of measuring electrons with energies capable of penetrating shielding, it was necessary to check the performance of the instrument. Fortunately, in the mid-magnetosphere region particle intensities are such that the EPD instrument operated within its range of accurate counting. Salient results include: 1. Intensities that diminish exponentially with radial distance from 10 to approximately 18 [R.sub.J], with > 1 MeV electrons e-folding in about 1.9 [R.sub.J] and > 10 MeV electrons in about 1.2 [R.sub.J]. 2. A much more gradual decrease beyond 18 [R.sub.J] (e-folding in about 9.6 [R.sub.J] for > 1 MeV and about 5.3 [R.sub.J] for > 10 MeV. 3. A persistent intensity modulation at the planetary rotation period most strongly evident in the 10-18 [R.sub.J] region. 4. Secular variations that can be as large as factors of 100 most strongly evident in the 18-40 [R.sub.J] region. 5. Near order of magnitude variations of flux with magnetic latitude in the mid-magnetosphere, 24-25 [R.sub.J] between latitudes 0[degrees] and 15[degrees]. This manuscript describes the analysis and provides further detail on the results. Keywords: Jupiter, magnetosphere; Magnetospheres

We report on two-dimensional imaging observations of D-line emissions from the extended distribution of iogenic sodium atoms with two fields of view ([+ or -] 20 [R.sub.J] (narrow FOV) and [+ or -] 400 [R.sub.J] (wide FOV)) simultaneously by using a portable small telescope or camera lens. We derived dynamic feature of the band-shaped and spray-shaped distributions near Io's orbit by means of continuous observation. The observations confirm the phenomenological behavior of the sodium cloud on two spatial scales, as previously observed by Pilcher et al. [Pilcher, C.B., Smyth, W.H., Combi, M.R., Fertel, J.H., 1984. Astrophys. J. 287, 427-444], Schneider et al. [Schneider, N.M., Trauger, J.T., Wilson, J.K., Brown, D.I., Evans, R.W., Shemansky, D.E., 1991. Science 253, 1394-1397], and Mendillo et al. [Mendillo, M., Baumgartner, J., Flynn, B., Hughes, W.S., 1990. Nature 348, 312-314]. We also confirm an elongated oval emission distribution of the sodium nebula and derivation of its detailed east-west asymmetry depending on Io's phase angle, which was first noted by Flynn et al. [Flynn, B., Mendillo, M., Baumgartner, J., 1994. J. Geophys. Res. 99, 8403-8409]. We then did model analyses to investigate the source process for sodium atoms and the dynamics behind their distribution. We conclude that the essential of molecular ion mechanisms to the band-shaped distribution is in agreement with Wilson and Schneider [Wilson, J.K., Schneider, N.M., 1999. J. Geophys. Res. 104, 16567-16583]. We differ from Wilson et al. [Wilson, J.K., Mendillo, M., Baumgartner, J., Schneider, N.M., Trauger, J.T., Flynn, B., 2002. Icarus 157, 476-489] in finding that charge exchange process contributes more to the spray-shaped distribution and sodium nebula than sputtering does. These results derived the double-peaked velocity distribution of released sodium atoms, and re-confirmed the source rates in agreement with past studies. Keywords: Io; Satellites, atmospheres; Jupiter, Magnetosphere

We have analyzed the Cassini Ultraviolet Imaging Spectrometer (UVIS) observations of the Jupiter aurora with an auroral atmosphere two-stream electron transport code. The observations of Jupiter by UVIS took place during the Cassini Campaign. The Cassini Campaign included support spectral and imaging observations by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS). A major result for the UVIS observations was the identification of a large color variation between the far ultraviolet (FUV: 1100-1700 [Angstrom]) and extreme ultraviolet (EUV: 800-1100 [Angstrom]) spectral regions. This change probably occurs because of a large variation in the ratio of the soft electron flux (10-3000 eV) responsible for the EUV aurora to the hard electron flux (~15-22 keV) responsible for the FUV aurora. On the basis of this result a new color ratio for integrated intensities for EUV and FUV was defined (4[pi][.sub.1550-1620 [Angstrom]]/4[pi] [I.sub.11030-1150 [Angstrom]]) which varied by approximately a factor of 6. The FUV color ratio (4[pi][.sub.1550-1620 [Angstrom]]/4[pi][.sub.1230-1300 [Angstrom]]) was more stable with a variation of less than 50% for the observations studied. The medium resolution (0.9 [Angstrom] FWHM, G140M grating) FUV observations (1295-1345 [Angstrom] and 1495-1540 [Angstrom]) by STIS on 13 January 2001, on the other hand, were analyzed by a spectral modeling technique using a recently developed high-spectral resolution model for the electron-excited [H.sub.2] rotational lines. The STIS FUV data were analyzed with a model that considered the Lyman band spectrum ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]) as composed of an allowed direct excitation component ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]) and an optically forbidden component ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] followed by the cascade transition ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]). The medium-resolution spectral regions for the Jupiter aurora were carefully chosen to emphasize the cascade component. The ratio of the two components is a direct measurement of the mean secondary electron energy of the aurora. The mean secondary electron energy of the aurora varies between 50 and 200 eV for the polar cap, limb and auroral oval observations. We examine a long time base of Galileo Ultraviolet Spectrometer color ratios from the standard mission (1996-1998) and compare them to Cassini UVIS, HST, and International Ultraviolet Explorer (IUE) observations. Keywords: Spectroscopy; Jupiter magnetosphere; Jupiter atmosphere; Ultraviolet observations

Seismology is the best tool for investigating the interior structure of stars and giant planets. This paper deals with a photometric study of jovian global oscillations. The propagation of acoustic waves in the jovian troposphere is revisited in order to estimate their effects on the planetary albedo. According to the standard model of the jovian cloud structure there are three major ice cloud layers (e.g., [Atreya et al., 1999. A comparison of the atmospheres of Jupiter and Saturn: Deep atmospheric composition, cloud structure, vertical mixing, and origin. Planet Space Sci. 47, 1243-1262]). We consider only the highest layers, composed of ammonia ice, in the region where acoustic waves are trapped in Jupiter's atmosphere. For a vertical wave propagating in a plane parallel atmosphere with an ammonia ice cloud layer, we calculate first the relative variations of the reflected solar flux due to the smooth oscillations at about the ppm level. We then determine the phase transitions induced by the seismic waves in the clouds. These phase changes, linked to ice particle growth, are limited by kinetics. A Mie model [Mishchenko et al., 2002. Scattering, Absorption, and Emission of Light by Small Particles. Cambridge Univ. Press, Cambridge, pp. 158-190] coupled with a simple radiation transfer model allows us to estimate that the albedo fluctuations of the cloud perturbed by a seismic wave reach relative variations of 70 ppm for a 3-mHz wave. This albedo fluctuation is amplified by a factor of ~70 relative to the previously published estimates that exclude the effect of the wave on cloud properties. Our computed amplifications imply that jovian oscillations can be detected with very precise photometry, as proposed by the microsatellite JOVIS project, which is dedicated to photometric seismology [Mosser et al., 2004. JOVIS: A microsatellite dedicated to the seismic analysis of Jupiter. In: Combes, F., Barret, D., Contini, T., Meynadier, F., Pagani, L. (Eds.), SF2A-2004, Semaine de l'Astrophysique Francaise, Les Ulis. In: EdP-Sciences Conference Series, pp. 257-258]. Keywords: Jupiter; Jupiter, atmosphere; Atmosphere, dynamics; Photometry

The temperatures in Jupiter's stratosphere, as measured by the Galileo Atmosphere Structure Instrument (ASI), show fluctuations that have been interpreted as gravity waves. We present a detailed description of these fluctuations, showing that they are not likely to be due to either measurement error or isotropic turbulence. These fluctuations share features with gravity waves observed in the terrestrial middle atmosphere, including the shape and amplitude of the power spectrum of temperature with respect to vertical wavenumber. Under the gravity wave interpretation, we find that wave heating or cooling is likely to be important in Jupiter's upper stratosphere and unimportant in the lower stratosphere. Keywords: Atmospheres, dynamics; Jupiter, atmosphere

We use the fully coupled, three-dimensional, global circulation Jovian Ionospheric Model (JIM) to calculate the coupling between ions in the jovian auroral ovals and the co-existing neutral atmosphere. The model shows that ions subject to drift motion around the auroral oval, as a result of the E x B coupling between a meridional, equatorward electric field and the jovian magnetic field, generate neutral winds in the planetary frame of reference. Unconstrained by the magnetic field, these neutral winds have a greater latitudinal extent than the corresponding ion drifts. Values of the coupling coefficient, k (h), are presented as a function of altitude and cross-auroral electric field strength, for different incoming electron fluxes and energies. The results show that, with ion velocities of several hundred metres per second to over 1 kms -1, k(h) can attain values greater than 0.5 at the ion production peak. This parameter is key to calculating the effective conductivities required to model magnetosphere-ionosphere coupling correctly. The extent to which angular momentum (and therefore energy) is transported vertically in JIM is much more limited than earlier, one-dimensional, studies have predicted. Keywords: Aurora; Ionospheres; Jupiter, atmosphere; Jupiter, magnetosphere; Modelling

We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 [micro]m, combined with high spectral resolution (0.2 [cm.sup.-1]), allowed us to map emission from the [H.sub.2] [S.sub.1] (1) quadrupole line and from several [H.sub.3]+ lines. The [H.sub.2] and [H.sub.3]+ emission appears to be morphologically different, especially in the north, where the latter notably exhibits a 'hot spot' near 150[degrees]-170[degrees] System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform [H.sub.2] [S.sub.1] (1) emission. We also present the first images of the [H.sub.2] emission in the southern polar region. The spectra include a total of 14 [H.sub.3]+ lines, including two hot lines from the 3[v.sub.2]-[v.sub.2] band, detected on Jupiter for the first time. They can be used to determine [H.sub.3]+ column densities, rotational (Trot) and vibrational ([T.sub.vib]) temperatures. We find the mean [T.sub.vib] of the [v.sub.2] = 3 state to be lower (960 [+ or -] 50 K) than the mean [T.sub.rot] in [v.sub.2] = 2 (1170 [+ or -] 75 K), indicating an underpopulation of the [v.sub.2] = 3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from [v.sub.2] observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, [T.sub.vib] and column densities, indicates that variations in line intensities are mostly due to correlated variations in the [H.sub.3]+ column densities. The thermostatic role played by [H.sub.3]+ at ionospheric levels may provide an explanation. The exception is the northern 'hot spot,' which exhibits a [T.sub.vib] about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the [H.sub.2] and [H.sub.3]+ emission are equally difficult to explain. Keywords: Jupiter; Jupiter/atmosphere; Ionospheres infrared observations

Two-dimensional model calculations (altitude and solar zenith angle) are performed to investigate the impact of electron chemistry on the composition and structure of Io's atmosphere. The calculations are based upon the model of Wong and Smyth (2000, Icarus 146, 60-74) for Io's S[O.sub.2] sublimation atmosphere with the addition of new electron chemistry, where the interactions of the electrons and neutrals are treated in a simple fashion. The model calculations are presented for Io's atmosphere at western elongation (dusk ansa) for both a low-density case (subsolar temperature of 113 K) and a high-density case (subsolar temperature of 120 K). The impact of electron-neutral chemistry on the composition and structure of Io's atmosphere is confined primarily to an interaction layer. The penetration depth of the interaction layer is limited to high altitudes in the thicker dayside atmosphere but reaches the surface in the thinner dayside and/or nightside atmosphere at larger solar zenith angles. Within most of the thicker dayside atmosphere, the column density of S[O.sub.2] is not significantly altered by electrons, but in the interaction layer all number densities are significantly altered: S[O.sub.2] is reduced, O, SO, S, and [O.sub.2] are greatly enhanced, and O, SO, and S become comparable to S[O.sub.2] at high altitudes. For the thinner nightside atmosphere, the species number densities are dramatically altered: S[O.sub.2] is drastically reduced to the least abundant species of the S[O.sub.2] family, SO and [O.sub.2] are significantly reduced at all altitudes, and O and S are dramatically enhanced and become the dominant species at all altitudes except near the surface. The interaction layer also defines the location of the emission layer for neutrals excited by electron impact and hence determines the fraction of the total neutral column density that is visible in remote observation. Electron chemistry may also impact the ratio of the equatorial to polar S[O.sub.2] column density deduced from Lyman-[alpha] images and the north-south alternating and System III longitude-dependent asymmetry observed in polar O and S emissions. eywords: Io; Satellites, atmospheres; Atmospheres, structure; Atmospheres, composition; Satellites of Jupiter

We present a technique for creating a longitude-resolved image of Jupiter's thermal radio emission. The technique has been applied to VLA data taken on 25 January 1996 at a wavelength of 2 cm. A comparison with infrared data shows a good correlation between radio hot spots and the 5 [micro]m hot spots seen on IRTF images. The brightest spot on the radio image is most likely the hot spot through which the Galileo probe entered Jupiter's atmosphere. We derived the ammonia abundance (= volume mixing ratio) in the hot spot, which is ~ 3 x [10.sup.-5], about half that seen in longitude-averaged images of the NEB, or less than 1/3 of the longitude-averaged ammonia abundance in the EZ. This low ammonia abundance probably extends down to at least the 4 bar level. Keywords: Jupiter, atmosphere; Data reduction techniques

We present a summary of Jupiter data taken over an eighteen year span (1981-1998) by the Very Large Array at ~ 21.0 cm. At this wavelength the emission is dominated by synchrotron radiation, which is roughly proportional to the product of the electron number density and magnetic field strength ([N.sub.e] B). At each epoch 8-12 hours of data were taken, which allowed us to examine Jupiter during an entire rotation period. We mapped the longitudinal structure of the synchrotron radiation by using a 3D reconstruction technique developed by Sault et al. [Astron. Astrophys. 324 (1997) 1190] which enabled us to produce plots of the latitude, radial distance, and peak intensity vs. jovian longitude (System III). The results show the shape of the synchrotron radiation has remained stable (except, of course, during the period of comet Shoemaker-Levy 9 impacts). Specifically, the latitudinal structure has remained nearly constant. Furthermore, the general dependence of the radial intensity profile has remained the same throughout the years, though radial distance has slightly, though significantly, changed. This constancy implies that the spatial structure of both the particle distribution and magnetic field have varied little over the eighteen year span. The primary changes in the synchrotron radiation have been seen in the intensity of emission as a function of time. There are certain epochs (e.g., 1987) which show more emissivity than others (e.g., 1981, 1995) at all longitudes. When each epoch is longitudinally averaged, there may be an anti-correlation between the radial distance and corresponding peak intensities of the synchrotron radiation, as one might expect if radial diffusion is important. We examine these trends by comparing the data to plots of the total intensity at 13 cm (by Klein et al., in: Rucker, H.O., et al., Planetary Radio Emissions V. Austrian Acad. Sci. Press, Vienna, p. 221). Overall, variations in our 21-cm data are similar to those measured at 13 cm, but there appears to be a change in spectral index and perhaps in the spatial brightness distribution in 1992. We attribute this to a change in both the spatial and energy distribution of the relativistic electrons. Keywords: Jupiter; Magnetosphere; Radio observations

This paper presents the first detailed analysis of acetylene absorption features observed longward of 190.0 nm in a jovian spectrum by the Faint Object Spectrograph on board the Hubble Space Telescope. The presence of two features located near 207.0 nm can only be explained by a substantial abundance of acetylene in the upper troposphere. Using a Rayleigh--Raman radiative transfer model, it was determined that the acetylene vertical profile is characterized by a decrease in the mole fraction with increasing pressure in the upper stratosphere, a minimum around 14 to 29 mbar, followed by an increase to about 1.5 x [10.sup.-7] in the upper troposphere. Longward of 220 nm, the relatively high contrast of Raman features to the continuum precludes the existence of an optically significant amount of clouds from 150 to 500 mbar unless they are highly reflective. Instead, the reflectivity at these long wavelengths is determined by stratospheric, not tropospheric, scatterers and absorbers. Analysis of the data also suggests that ammonia is extremely undersaturated at pressures below 700 mbar. However, no firm conclusions can be reached because of the uncertainties surrounding its cross section longward of 217.0 nm, which are due to vibrationally excited states. Keywords: Jupiter; atmosphere; Spectroscopy; Radiative transfer; UV observations

We observed Jupiter's synchrotron radiation at frequencies of 15 and 22 GHz using the VLA (Very Large Array) in its most compact configuration (D-array) in March 1991. The spatial brightness distribution of the emission at these high frequencies appears to be very similar to that seen at lower frequencies (5 GHz down to 330 MHz). We measured a total nonthermal flux density at 15 and 22 GHz of 1.5 [+ or -] 0.15 Jy and 1.5 [+ or -] 0.4 Jy, respectively (both normalized to a geocentric distance of 4.04 AU). These numbers agree well with model spectra of Jupiter's synchrotron radiation that were obtained by fitting the planet's nonthermal radio emission between 74 MHz and 8 GHz and suggest a maximum cutoff in electron energies at ~100 MeV. The degree of linear polarization observed with the VLA is 21.5 [+ or -] 1.9% at 15 GHz. Keywords: Jupiter; Magnetosphere; Radio observations

We carried out a brief campaign in September 1998 to determine Jupiter's radio spectrum at frequencies spanning a range from 74 MHz up to 8 GHz. Eleven different telescopes were used in this effort, each uniquely suited to observe at a particular frequency. We find that Jupiter's spectrum is basically flat shortwards of 1-2 GHz, and drops off steeply at frequencies greater than 2 GHz. We compared the 1998 spectrum with a spectrum (330 MHz-8 GHz) obtained in June 1994, and report a large difference in spectral shape, being most pronounced at the lowest frequencies. The difference seems to be linear with log(v), with the largest deviations at the lowest frequencies (v). We have compared our spectra with calculations of Jupiter's synchrotron radiation using several published models. The spectral shape is determined by the energy-dependent spatial distribution of the electrons in Jupiter's magnetic field, which in turn is determined by the detailed diffusion process across L-shells and in pitch angle, as well as energy-dependent particle losses. The spectral shape observed in September 1998 can be matched well if the electron energy spectrum at L = 6 is modeled by a double power law [E.sup.-a] (1 + [(E/[E.sub.0])).sup.-b], with a = 0.4, b = 3, [E.sub.0] = 100 MeV, and a lifetime against local losses [[tau].sub.0] = 6 x [10.sup.7] s. In June 1994 the observations can be matched equally well with two different sets of parameters: (1) a = 0.6, b = 3, [E.sub.0] = 100 MeV, [[tau].sub.0] = 6 x [10.sup.7] s, or (2) a = 0.4, b = 3, [E.sub.0] = 100 MeV, [[tau].sub.0] = 8.6 x [10.sup.6] s. We attribute the large variation in spectral shape between 1994 and 1998 to pitch angle scattering, coulomb scattering and/or energy degradation by dust in Jupiter's inner radiation belts. Keywords: Jupiter; Magnetosphere; Radio observations

We present the first images and measurement of flux density of Jupiter at a frequency of 74 MHz, obtained with the Very Large Array in September 1998. We observed simultaneously at frequencies of 74 and 330 MHz. We compare our data with observations taken during the same time at other frequencies (presented by de Pater and 13 others, 2003, Icarus 163, 434-448) and show that the spectrum of Jupiter appears to flatten, or perhaps turn over, at lower frequencies. Keywords: Jupiter; Magnetosphere; Radio observations

Thunderstorms in Jupiter's atmosphere are likely to be prodigious generators of acoustic waves, as are thunderstorms in Earth's atmosphere. Accordingly, we have used a numerical model to study the dissipation in Jupiter's thermosphere of upward propagating acoustic waves. Model simulations are performed for a range of wave periods and horizontal wavelengths believed to characterize these acoustic waves. The possibility that the thermospheric waves observed by the Galileo Probe might be acoustic waves is also investigated. Whereas dissipating gravity waves can cool the upper thermosphere through the effects of sensible heat flux divergence, it is found that acoustic waves mainly heat the Jovian thermosphere through effects of molecular dissipation, sensible heat flux divergence, and Eulerian drift work. Only wave-induced pressure gradient work cools the atmosphere, an effect that operates at all altitudes. The sum of all effects is acoustic wave heating at all heights. Acoustic waves and gravity waves heat and cool the atmosphere in fundamentally different ways. Though the amplitudes and mechanical energy fluxes of acoustic waves are poorly constrained in Jupiter's atmosphere, the calculations suggest that dissipating acoustic waves can locally heat the thermosphere at a significant rate, tens to a hundred Kelvins per day, and thereby account for the high temperatures of Jupiter's upper atmosphere. It is unlikely that the waves detected by the Galileo Probe were acoustic waves; if they were, they would have heated Jupiter's thermosphere at enormous rates.

In early 1998 two of the three, long-lived anticyclonic, jovian white ovals merged. In 2000 the two remaining white ovals merged into one. Here we examine that behavior, as well as the dynamics of three earlier epochs: the Formation Epoch (1939-1941), during which a nearly axisymmetric band broke apart to form the vortices; the Karman Vortex Street Epoch (1941-1994), during which the white ovals made up the southern half of two rows of vortices, and their locations oscillated in longitude such that the white ovals often closely approached each other but did not merge; and the Pre-merger Epoch (1994-1997), during which the three white ovals traveled together with intervening cyclones from the northern row of the Karman vortex street in a closely spaced group with little longitudinal oscillation. We use a quasi-geostrophic model and large-scale numerical simulation to explain the dynamics. Our models and simulations are consistent with the observations, but none of the observed behavior is even qualitatively possible without assuming that there are long-lived, coherent cyclones longitudinally interspersed with the white ovals. Without them, the white ovals approach each other and merge on a fast, advective timescale (4 months). A necessary ingredient that allows the vortices to travel together in a small packet without spreading apart is that the strong, eastward-flowing jetstream south of the white ovals is coincident with a sharp gradient in background potential vorticity. The jet forms a Rossby wave and a trough of the wave traps the white ovals. In our simulations, the three white ovals were trapped before they merged. Without being trapped, the amount of energy needed to perturb two white ovals so that they merge exceeds the atmosphere's turbulent energy (which corresponds to velocities of ~1 m [s.sup.-1]) by a factor of ~100. The mergers of the white ovals BC and DE were not observed directly, so there is ambiguity in labeling the surviving vortices and identifying which vortices might have exchanged locations. The simulation and modeling make the identifications clear. They also predict the fate of the surviving white oval and of the other prominent jovian vortex chains. Keywords: Jupiter; Atmosphere; Dynamics; White oval spots

This work presents a six-year study aimed at characterizing the morphology and properties of the atmospheric features present in jovian cyclonic regions. It complements our previous analysis for the same period on the anticyclonic vortices (Morales-Juberias et al. 2002, Icarus 157, 76-90). The main difference between cyclonic and anticyclonic regions in Jupiter is that a variety of organized morphologies are present in the cyclonic areas, although they can be grouped consistently into five different types: filamentary turbulence related to the highest speed jets, organized folded filamentary regions, elongated areas with contours closed by a ribbon-like feature, discrete, closed brown cyclones ('barges'), and peculiar transient structures such as short wave trains and cyclonic cells. We present data on their color contrast, size, aspect ratio, distribution, lifetimes, relation to the jet system and to the anticyclones, and motions (global and internal to the features). Most cyclonic features show a rapid evolution, compared to the anticyclones, and tend to be dispersed zonally although some survive for a few years. We used the barges that are the most representative, long-lived, and extended type of cyclonic features to show that there exists a linear relationship between their relative velocity and the mean zonal flow speed, similar to that found in our previous work on the anticyclones. There is also some evidence that the drift rate of barges is related to the planetary minus flow vorticity gradient. Key Words: Jupiter; atmosphere; dynamics; meteorology.

Recent work has been concerned with calculating the three-dimensional ion concentrations and Pedersen and Hall conductivities within the auroral region of Jupiter for varying conditions of incident electron precipitation. Using the jovian ionospheric model, we present results that show the auroral ionospheric response to changing the incoming flux of precipitating electrons (for constant initial energy) and also the response to changing the initial energy (for both constant flux and constant energy flux). The results show that, for expected energy fluxes of precipitating particles, the average auroral integrated Pedersen conductivity attains values in excess of 1 mho. In addition, it is shown that electrons with an initial energy of around 60 keV are particularly effective at generating auroral conductivity: Particles of this energy penetrate most effectively to the layer of the jovian ionosphere at which the auroral conductivity is at a maximum. Key Words: aurorae; ionospheres; Jupiter, atmosphere; Jupiter, magnetosphere; modelling.

Observations of [H.sub.2]O rotational lines from the Infrared Space Observatory (ISO) and the Submillimeter Wave Astronomy Satellite (SWAS) and of the C[O.sub.2] [v.sub.2] band by ISO are analyzed jointly to determine the origin of water vapor and carbon dioxide in Jupiter's stratosphere. Simultaneous modelling of ISO/LWS and ISO/SWS observations acquired in 1997 indicates that most of the stratospheric jovian water is restricted to pressures less than 0.5 [+ or -] 0.2 mbar, with a disk-averaged column density of (2.0 [+ or -] 0.5) x [10.sup.15] [cm.sup.-2]. Disk-resolved observations of C[O.sub.2] by ISO/SWS reveal latitudinal variations of the C[O.sub.2] abundance, with a decrease of at least a factor of 7 from mid-southern to mid-northern latitudes, and a disk-center column density of (3.4 [+ or -] 0.7) x [10.sup.14] [cm.sup.-2]. These results strongly suggest that the observed [H.sub.2]O and C[O.sub.2] primarily result from the production, at midsouthern latitudes, of oxygenated material in the form of CO and [H.sub.2]O by the Shoemaker-Levy 9 (SL9) impacts in July 1994 and subsequent chemical and transport evolution, rather than from a permanent interplanetary dust particle or satellite source. This conclusion is supported by quantitative evolution model calculations. Given the characteristic vertical mixing times in Jupiter's stratosphere, material deposited at ~0.1 mbar by the SL9 impacts is indeed expected to diffuse down to the ~0.5 mbar level after 3 years. A coupled chemical-horizontal transport model indicates that the stability of water vapor against photolysis and conversion to C[O.sub.2] is maintained over typically ~50 years by the decrease of the local CO mixing ratio associated with horizontal spreading. A model with an initial (i.e., SL9-produced) [H.sub.2]O/CO mass mixing ratio of 0.07, not inconsistent with immediate postimpact observations, matches the observed [H.sub.2]O abundance and C[O.sub.2] horizontal distribution 3 years after the impacts. In contrast, the production of C[O.sub.2] from SL9-produced CO and a water component deriving from an interplanetary dust component is insufficient to account for the observed C[O.sub.2] amounts. The observations can further be used to place a stringent upper limit (8 x [10.sup.4] [cm.sup.-2] [s.sup.-1]) on the permanent water influx into Jupiter. This may indicate that the much larger flux observed at Saturn derives dominantly from a ring source, or that the ablation of micrometeoroids leads dominantly to different species at Saturn ([H.sub.2]O) and Jupiter (CO). Finally, the SWAS [H.sub.2]O spectra do not appear fully consistent with the ISO data and should be confirmed by future ODIN and Herschel observations. Key Words: Jupiter's atmosphere; spectroscopy.

Thirteen lines of the CO band near 4.7 [micro]m have been observed on a jovian hot spot at a resolution of 0.045 [cm.sup.-1]. The measured line profiles indicate that the CO mole fraction is 1.0 [+ or -] 0.2 ppb around the 6-bar level and is larger in the upper troposphere and/or stratosphere. An external source of CO providing an abundance of [4.sup.+3.sub.-2] x [10.sup.16] molecules [cm.sub.-2] is implied by the observations in addition to the amount deposited at high altitude by the Shoemaker-Levy 9 collision. From a simple diffusion model, we estimate that the CO production rate is (1.5-10)x [10.sup.6] molecules [cm.sup.-2] [s.sup.-1] assuming an eddy diffusion coefficient around the tropopause between 300 and 1500 [cm.sup.2] [s.sup.-1]. Precipitation of oxygen atoms from the jovian magnetosphere or photochemistry of water vapor from meteoroidal material can only provide a negligible contribution to this amount. A significant fraction of the CO in Jupiter's upper atmosphere may be formed by shock chemistry due to the infall of kilometer- to subkilometer-size Jupiter family comets. Using the impact rate from Levison et al. (2000, Icarus 143, 415-420) rescaled by Bottke et al. (2002, Icarus 156, 399-433), this source can provide the observed stratospheric CO only if the eddy diffusion coefficient around the tropopause is 100-300 [cm.sup.2] [s.sup.-1]. Higher values, ~700 [cm.sup.2] [s.sup.-1], would require an impact rate larger by a factor of 5-10, which cannot be excluded considering uncertainties in the distribution of Jupiter family comets. Such a large rate is indeed consistent with the observed cratering record of the Galilean satellites (Zahnle et al. 1998, Icarus 13b, 202-222). On The other hand, the ~1 ppb concentration in the lower troposphere requires an internal source. Revisiting the disequilibrium chemistry of CO in Jupiter, we conclude that rapid vertical mixing can provide the required amount of CO at ~6 bar for a global oxygen abundance of 0.2-9 times the solar value considering the uncertainties in the convective mixing rate and in the chemical constants. Key Words: Jupiter, atmosphere; infrared observations; atmospheres, composition.

We report the first spectroscopic detection of discrete ammonia ice clouds in the atmosphere of Jupiter, as discovered utilizing the Galileo Near-Infrared Mapping Spectrometer (NIMS). Spectrally identifiable ammonia clouds (SIACs) cover less than 1% of the globe, as measured in complete global imagery obtained in September 1996 during Galileo's second orbit. More than half of the most spectrally prominent SIACs reside within a small latitudinal band, extending from 2[degrees] to 7[degrees] N latitude, just south of the 5-[micro]m hot spots. The most prominent of these are spatially correlated with nearby 5-[micro]m-bright hot spots lying 1.5[degrees]-3.0[degrees] of latitude to the north: they reside over a small range of relative longitudes on the eastward side of hot spots, about 37% of the longitudinal distance to the next hot spot to the east. This strong correlation between the positions of hot spots and the most prominent equatorial SIACs suggests that they are linked by a common planetary wave. Good agreement is demonstrated between regions of condensation predicted by the Rossby wave model of A. J. Friedson and G. S. Orton (1999, Bull. Am. Astron. Assoc 31, 1155-1156) and the observed longitudinal positions of fresh ammonia clouds relative to 5-[micro]m hot spots. Consistency is also demonstrated between (1) the lifetime of particles as determined by the wave phase speed and cloud width and (2) the sedimentation time for 10-[micro]m radius particles consistent with previously reported ammonia particle size by T. Y. Brooke et al. (1998, Icarus 136, 1-13). A young age ( Key Words: atmospheres, composition; atmospheres, dynamics; ices; Jupiter, atmosphere; spectrophotometry.

Galileo Probe Atmospheric Structure Investigation (ASI) pressure and temperature sensor data acquired during the parachute descent phase have been used to derive the static stability structure of Jupiter's troposphere at pressure levels of 0.5-22 bars using three techniques. The first approach utilizes both the p-sensor and T-sensor data, but since the p-sensor's zero offset was significantly affected by the thermal anomaly in the probe, two other approaches using only T-sensor data have also been developed. By making the physically reasonable assumptions of equilibrium descent for the probe and hydrostatic balance of the atmosphere, an algorithm for deriving the background static stability from T-sensor measurements alone is developed. Regions with static stability 0.1-0.2 K km-1 are found at 0.5-1.7 bars, 3-8.5 bars, and 14-20 bars. Between these layers, regions of weaker static stability are present. Mean molecular weight gradients due to the vertical variation of water vapor abundance near the 11-bar pressure level appear to stabilize the atmosphere at this level. Oscillatory structures with vertical wavelength ~15-30 km and amplitude ~0.1-0.2 K are observed in the T-sensor data. For pressure Key Words: atmospheres, structure; atmospheres, dynamics; Jupiter, atmosphere.

We present coupled chemical-microphysical models for the formation, growth, and physical properties of the jovian polar haze based on a gas-phase photochemical model for the auroral regions developed by A. S. Wong et al. (2000, Astrophys. J. 534, L215-217). In this model, auroral particle precipitation provides an important energy source for enhanced decomposition of methane and production of benzene and polycyclic aromatic hydrocarbons (PAHs). We find that at high altitude, [A.sub.4] (pyrene, a hydrocarbon consisting of four fused aromatic rings) should homogeneously nucleate to form tiny primary particles. At lower altitudes, [A.sub.3] (phenanthrene) and [A.sub.2] (naphthalene) heterogeneously nucleate on the [A.sub.4] nuclei. These particles subsequently grow by additional condensation of [A.sub.2] on the nucleated particles and by coagulation and eventually sediment out to the troposphere. We run different cases of the aerosol microphysical model for different assumptions regarding the fractal dimension of aggregate particles formed by the coagulation process. If coagulation is assumed to produce spherical particles (of dimensionality 3), then their mean radius at altitudes below the 20-mbar pressure level is computed to be approximately 0.1 [micro]m. If coagulation produces fractal aggregates of dimension 2.1, then their equivalent mean radius below the 20-mbar level is much larger, of order 0.7 [micro]m. Aggregates with fractal dimensions between 2.1 and 3 form with equivalent mean radii between 0.1 and 0.7 [micro]m. In every case, mean particle radius is found to decrease with increasing altitude, as expected for a system approximately in sedimentation-coagulation equilibrium. The predicted range of altitudes where aerosol formation occurs and the mean size to which particles grow are found to be generally consistent with observations. However, our calculations cannot presently account for the large amount of total aerosol loading inferred by M. G. Tomasko et al. (1986, Icarus 65, 218-243). We suggest that the primarily neutral chemical pathway to heavy hydrocarbon and PAH formation proposed by Wong et al. (2000) may proceed too slowly to produce a sufficient amount of condensible material. Inclusion of ion and ion-neutral reactions in the chemical scheme could potentially lead to the prediction of higher PAH production rates, higher nucleation rates, and greater aerosol loading, producing better agreement with the observations. Key Words: Jupiter; atmosphere; photochemistry; aurorae.

Linear wave patterns in Jupiter's clouds with wavelengths strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere (F. M. Flasar and P. J. Gierasch, 1986, J. Atmos. Sci. 43, 2683-2707). We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds (A. P. Ingersoll and D. W. Koerner 1989, Bull. Am. Astron. Soc. 21, 943). We numerically analyze the linear stability of wavelike disturbances that have nonzero horizontal phase speeds in Jupiter's atmosphere and find that, if the static stability in the shear layer is very low (but still nonnegative), a deep vertical shear layer like the one measured by the Galileo probe (D. H. Atkinson et al. 1998, J. Geophys. Res. 103, 22911-22928) can generate the instabilities. The fastest growing waves grow exponentially within an hour, and their wavelengths match the observations. Close to zero values of static stability that permit the growth of instabilities are within the range of values measured by the Galileo probe in a hot spot (A. Seiff et al. 1998, J. Geophys. Res. 103, 22857-22889). Our model probes Jupiter's equatorial atmosphere below the cloud deck and suggests that thick regions of wind shear and low static stability exist outside hot spots. Key Words: Jupiter; jovian atmosphere; atmospheric dynamics; atmospheric structure.

The changing size and aspect ratio of the Great Red Spot from 1880 to 2000 are reviewed, indicating that the length of the system has decreased significantly over the last 100 years and continues to decrease at present at a rate of 0.19 degrees per year. Voyager IRIS maps of para hydrogen fraction and potential temperature over the system are presented, showing the internal structure and surrounding areas at pressures from 100 to 500 mbars. In these maps, the GRS appears as a cold temperature anomaly and a low para fraction anomaly. Vertical structure analyses and wind velocity measurements are presented from data acquired by the Galileo spacecraft in 1996 and 2000, respectively. The vertical structure data suggest a very thick, white, cloud deck with a top near 800 [+ or -] 100 mbars and an extended, blue-absorbing, optically thick haze up to about 200 mbars with a thin stratospheric haze above it. The wind field shows a substantial increase in the maximum tangential velocity from 150 to 190 m [s.sup.-1] over the Galileo time period. The vertical structure analyses from Galileo data and the wind and temperature fields from Voyager data all show evidence of a tilt to the Great Red Spot at the cloud deck from north to south and more subtly from east to west. The data support the hypothesis of the GRS as a tilted 'pancake' with temporal variability to the tilt. Key Words: Jupiter; atmosphere; atmospheres, dynamics; atmospheres, evolution; atmospheres, structure.

Over an 18-year period, seasonal changes in the north-south asymmetry of polarization at high latitudes of Jupiter have been revealed by polarimetric observations in blue light. The average seasonal difference in the polarization degree between north and south is positive and equal to about 0.5%. There is some relationship between seasonal variations in the observed difference and the seasonal north-south asymmetry in solar radiation incident on Jupiter's atmosphere. There are two maxima on the observed seasonal curve, falling on the jovian spring and autumn and coinciding correspondingly with positive and negative maxima of the heliographic latitude of Jupiter. Two possible explanations are discussed: seasonal changes in insolation and/or time-dependent magnetospheric influence on the polar events. Key Words: Jupiter; Jupiter, atmosphere; polarimetry.

The Galileo Probe sampled Jupiter's atmosphere at the edge of a 5-[micro]m hot spot, where it found very little cloud opacity above the 700 mb level. Only [tau] = 1-2 at [lambda] = 0.5 [micro]m was inferred from Net Flux Radiometer observations (Sromovsky et al. 1998, J. Geophys. Res. 103, 22,929-22,977), in seeming conflict with Chanover et al. (1997, Icarus 128, 294-305) who inferred [tau] = 6-8 above the 700 mb level (at [lambda] ~ 0.9 [micro]m) from 893-nm and 953-nm WFPC2 observations of a group of hot spots. Postulating a heterogeneous cloud structure is one way to resolve the conflict. We obtained a more satisfying resolution by reinterpretation of the HST observations with Probe-compatible assumptions about the vertical distribution of cloud particles. Assuming a physically thin upper (putative N[H.sub.3]) cloud with adjustable optical depth and effective pressure ([p.sub.eff] < 440 mb) and a physically thin midlevel (putative N[H.sub.4]SH) cloud with adjustable optical depth but a fixed pressure of 1.2 bars, we are able to fit WPFC2 observations with probe-consistent opacities in hot spot regions. With the same cloud pressures, but higher middle cloud opacities, we are even able to fit the visibly bright regions. Little variability is seen in the upper cloud. Best fits to October 1995 WFPC2 observations in dark regions (5-[micro]m hot spots) yielded [[tau].sub.upper] = 1.3-1.9 at 0.9 [micro]m and [p.sub.eff] = 240 mb - 270 mb, while in visibly bright regions between hot spots we obtained [[tau].sub.upper] = 1.6-2.2 and [p.sub.eff] = 250 mb - 290 mb. May 1996 observations yielded slightly higher values of [[tau].sub.upper] (1.8-2.3 and 2.0-2.8) and [p.sub.eff] (250 mb - 310 mb and 265 mb - 320 mb). We found that the most important variable parameter is the opacity of the middle cloud, which ranged from [tau] = 1, 2 in dark regions, to [tau] = 8-30 in bright regions. From limb darkening characteristics, we inferred a wavelength-dependent haze opacity ranging from 0.2 [+ or -] 0.05 at 660 nm to 0.35 [+ or -] 0.05 at 953 nm, and an effective haze pressure near 120 mb. We did not find it necessary to use low single scattering albedos that require effective imaginary indices, that are several orders of magnitude larger than the values of the main putative cloud components. Key Words: Jupiter; Jupiter, atmosphere; Jupiter, clouds.

We have used the Hubble Space Telescope archived images of Jupiter for the period 1994-2000, complemented by ground-based telescopic observations, to study in detail the long-term properties of synoptic-scale anticyclonic vortices (size > 1500 km, lifetime > months). We have also analyzed a set of Voyager 1 and 2 images obtained in 1979 to compare anticyclone properties from the two different periods. The latitudinal range covered by this survey spans 75 [degrees] N to 75 [degrees] S, encompassing 12 anticyclonic zones. We present data on vortex size, aspect ratio, number, latitude location, lifetime, motion, interaction, and morphology for more than 100 vortices. We study empirically the relation between these properties and the mean ambient zonal flow. We show that most of these properties are not related to latitude and location relative to the jet pattern. However, a significant linear anticorrelation is found when plotting vortex relative speed (vortex propagation speed minus zonal flow velocity) against the zonal flow velocity at the central latitude of each vortex. As the mean eastward flow increases its velocity within a given anticyclonic domain, vortex velocity becomes more westward. This relation holds for all anticyclones except those moving at high velocities (at latitudes 20 [degrees] S and 23 [degrees] N), whose origin appears to be of a different nature. Moreover, there is also some evidence that the drift rate could be connected to the planetary minus flow vorticity gradient (most conspicuous at 40 and 45 [degrees] N). We present simple dynamical interpretations of these observations. Key Words: Jupiter; atmosphere; dynamics; meteorology.

We present the first reported measurements of the intensity of a 'hotband' transition for the [H.sup.+.sub.3] molecular ion in the northern auroral/polar region of Jupiter. This transition is identified as the R(3, [4.sup.+]) line of the (2[v.sub.2]2(l = 0) [vector] v2) hotband, with a wavelength of 3.94895/[micro]m. This is the first time such a transition has been measured outside the laboratory, and the wavelength as measured on Jupiter is within the experimental accuracy of the lab measurement. This detection makes it possible to investigate [H.sup.+.sub.3] transitions that simultaneously originate from different vibrational levels. We use the intensity ratio between this line and the Q(1, [0.sup.-]) fundamental transition to derive effective vibrational temperatures, column densities, and total emission parameters as a function of position across the auroral/polar region. Effective temperatures range from ~900 to ~1250 K; an increase in average temperature during our observing run of ~100 K is noted. The derived temperatures are toward the high end or in excess of the auroral temperature range that has been reported in the literature to date. The relationship among emission intensity, temperature, and density is shown to be complex. This may reflect the nonthermalization of the vibrational levels at the gas densities prevailing in the jovian thermosphere. An alternative analysis allowing for this effect is presented. But this approach requires thermospheric temperatures to be 41500 K at the level that the majority of [H.sup.+.sub.3] is being produced, higher than has previously been proposed. Key Words: aurorae; infrared observations; ionospheres; Jupiter, atmosphere; spectroscopy.