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NASA's Spitzer Infrared Spectrometer (IRS) acquired mid-infrared (5-37 microns) disc-averaged spectra of Uranus very near to its equinox in December 2007. A mean spectrum was constructed from observations of multiple central meridian longitudes, spaced equally around the planet, which has provided the opportunity for the most comprehensive globally-averaged characterisation of Uranus' temperature and composition ever obtained (Orton et al., 2014 a [arXiv:1407.2120], b [arXiv:1407.2118]). In this work we analyse the disc-averaged spectra at four separate central meridian longitudes to reveal significant longitudinal variability in thermal emission occurring in Uranus' stratosphere during the 2007 equinox. We detect a variability of up to 15% at wavelengths sensitive to stratospheric methane, ethane and acetylene at the ~0.1-mbar level. The tropospheric hydrogen-helium continuum and deuterated methane absorption exhibit a negligible variation (less than 2%), constraining the phenomenon to the stratosphere. Building on the forward-modelling analysis of the global average study, we present full optimal estimation inversions (using the NEMESIS retrieval algorithm, Irwin et al., 2008 [10.1016/j.jqsrt.2007.11.006]) of the Uranus-2007 spectra at each longitude to distinguish between thermal and compositional variability. We found that the variations can be explained by a temperature change of less than 3 K in the stratosphere. Near-infrared observations from Keck II NIRC2 in December 2007 (Sromovsky et al., 2009 [arXiv:1503.01957], de Pater et al., 2011 [10.1016/j.icarus.2011.06.022]), and mid-infrared observations from VLT/VISIR in 2009 (Roman et al., 2020 [arXiv:1911.12830]), help to localise the potential sources to either large scale uplift or stratospheric wave phenomena., 26 pages, 21 figures, to be published in Icarus (accepted 2021-04-27)

A time-variable 1D photochemical model is used to study the distribution of stratospheric hydrocarbons as a function of altitude, latitude, and season on Uranus and Neptune. The results for Neptune indicate that in the absence of stratospheric circulation or other meridional transport processes, the hydrocarbon abundances exhibit strong seasonal and meridional variations in the upper stratosphere, but that these variations become increasingly damped with depth due to increasing dynamical and chemical time scales. At high altitudes, hydrocarbon mixing ratios are typically largest where the solar insolation is the greatest, leading to strong hemispheric dichotomies between the summer-to-fall hemisphere and winter-to-spring hemisphere. At mbar pressures and deeper, slower chemistry and diffusion lead to latitude variations that become more symmetric about the equator. On Uranus, the stagnant, poorly mixed stratosphere confines methane and its photochemical products to higher pressures, where chemistry and diffusion time scales remain large. Seasonal variations in hydrocarbons are therefore predicted to be more muted on Uranus, despite the planet’s very large obliquity. Radiative-transfer simulations demonstrate that latitude variations in hydrocarbons on both planets are potentially observable with future JWST mid-infrared spectral imaging. Our seasonal model predictions for Neptune compare well with retrieved C(2)H(2) and C(2)H(6) abundances from spatially resolved ground-based observations (no such observations currently exist for Uranus), suggesting that stratospheric circulation — which was not included in these models — may have little influence on the large-scale meridional hydrocarbon distributions on Neptune, unlike the situation on Jupiter and Saturn.

We present five epochs of WFC3 HST Jupiter observations taken between 2009–2016 and extract global zonal wind profiles for each epoch. Jupiter’s zonal wind field is globally stable throughout these years, but significant variations in certain latitude regions persist. We find that the largest uncertainties in the wind field are due to vortices or hot-spots, and show residual maps which identify the strongest vortex flows. The strongest year-to-year variation in the zonal wind profiles is the 24°N jet peak. Numerous plume outbreaks have been observed in the Northern Temperate Belt and are associated with decreases in the zonal velocity and brightness. We show that the 24°N jet peak velocity and brightness decreased in 2012 and again in late 2016, following outbreaks during these years. Our February 2016 zonal wind profile was the last highly spatially resolved measurement prior to Juno's first science observations. The final 2016 data were taken in conjunction with Juno’s perijove 3 pass on 11 December 2016, and show the zonal wind profile following the plume outbreak at 24°N in October 2016.

Recent analysis of Gemini-North/NIFS H-band (1.45 - 1.8 $\mu$m) observations of Uranus, recorded in 2010, with recently updated line data has revealed the spectral signature of hydrogen sulphide (H$_2$S) in Uranus's atmosphere (Irwin et al., 2018). Here, we extend this analysis to Gemini-North/NIFS observations of Neptune recorded in 2009 and find a similar detection of H$_2$S spectral absorption features in the 1.57 - 1.58 $\mu$m range, albeit slightly less evident, and retrieve a mole fraction of $\sim1-3$ ppm at the cloud tops. We find a much clearer detection (and much higher retrieved column abundance above the clouds) at southern polar latitudes compared with equatorial latitudes, which suggests a higher relative humidity of H$_2$S here. We find our retrieved H$_2$S abundances are most consistent with atmospheric models that have reduced methane abundance near Neptune's south pole, consistent with HST/STIS determinations (Karkoschka and Tomasko, 2011). We also conducted a Principal Component Analysis (PCA) of the Neptune and Uranus data and found that in the 1.57 - 1.60 $\mu$m range, some of the Empirical Orthogonal Functions (EOFs) mapped closely to physically significant quantities, with one being strongly correlated with the modelled H$_2$S signal and clearly mapping the spatial dependence of its spectral detectability. Just as for Uranus, the detection of H$_2$S at the cloud tops constrains the deep bulk sulphur/nitrogen abundance to exceed unity (i.e. $ > 4.4 - 5.0$ times the solar value) in Neptune's bulk atmosphere, provided that ammonia is not sequestered at great depths, and places a lower limit on its mole fraction below the observed cloud of (0.4 - 1.3) $\times 10^{-5}$. The detection of gaseous H$_2$S at these pressure levels adds to the weight of evidence that the principal constituent of the 2.5 - 3.5-bar cloud is likely to be H$_2$S ice., Comment: 13 Figures

We present a reanalysis of visible/near-infrared (480–930 nm) observations of Neptune, made in 2018 with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT) in Narrow Field Adaptive Optics mode, reported by Irwin et al., Icarus, 311, 2019. We find that the inferred variation of methane abundance with latitude in our previous analysis, which was based on central meridian observations only, underestimated the retrieval errors when compared with a more complete assessment of Neptune's limb darkening. In addition, our previous analysis introduced spurious latitudinal variability of both the abundance and its uncertainty, which we reassess here. Our reanalysis of these data incorporates the effects of limb-darkening based upon the Minnaert approximation model, which provides a much stronger constraint on the cloud structure and methane mole fraction, makes better use of the available data and is also more computationally efficient. We find that away from discrete cloud features, the observed reflectivity spectrum from 800 to 900 nm is very well approximated by a background cloud model that is latitudinally varying, but zonally symmetric, consisting of a H2S cloud layer, based at 3.6–4.7 bar with variable opacity and scale height, and a stratospheric haze. The background cloud model matches the observed limb darkening seen at all wavelengths and latitudes and we find that the mole fraction of methane at 2–4 bar, above the H2S cloud, but below the methane condensation level, varies from 4–---6% at the equator to 2–4% at south polar latitudes, consistent with previous analyses, with a equator/pole ratio of 1.9 ± 0.2 for our assumed cloud/methane vertical distribution model. The spectra of discrete cloudy regions are fitted, to a very good approximation, by the addition of a single vertically thin methane ice cloud with opacity ranging from 0 to 0.75 and pressure less than ~0.4 bar.

High signal-to-noise images of Jupiter were made at wavelengths between 13.2 and 22.8 µm in five separate observing runs between 1996 June and 1997 November at the NASA Infrared Telescope Facility. Maps of Jupiter’s upper-tropospheric temperatures at pressures of 100 and 400 mbar were made from these images. We use the relatively frequent, well sampled data sets to examine in detail the short-term evolution of the temperature structure. Our 2–6 month sampling periods demonstrate that the longitudinal temperature structures evolve significantly in these short periods and exhibit wave features. Using a three-dimensional general circulation model simulation of Jupiter’s upper atmosphere, we show that the thermal structures are consistent with convectively generated Rossby waves that propagate upward from the lower to the upper atmosphere.

Recent work by Sromovsky et al. (2017, Icarus 291, 232-244) suggested that all red colour in Jupiter's atmosphere could be explained by a single colour-carrying compound, a so-called 'universal chromophore'. We tested this hypothesis on ground-based spectroscopic observations in the visible and near-infrared (480-930 nm) from the VLT/MUSE instrument between 2014 and 2018, retrieving a chromophore absorption spectrum directly from the North Equatorial Belt, and applying it to model spatial variations in colour, tropospheric cloud and haze structure on Jupiter. We found that we could model both the belts and the Great Red Spot of Jupiter using the same chromophore compound, but that this chromophore must exhibit a steeper blue-absorption gradient than the proposed chromophore of Carlson et al. (2016, Icarus 274, 106-115). We retrieved this chromophore to be located no deeper than 0.2+/-0.1 bars in the Great Red Spot and 0.7+/-0.1 bars elsewhere on Jupiter. However, we also identified some spectral variability between 510 nm and 540 nm that could not be accounted for by a universal chromophore. In addition, we retrieved a thick, global cloud layer at 1.4+/-0.3 bars that was relatively spatially invariant in altitude across Jupiter. We found that this cloud layer was best characterised by a real refractive index close to that of ammonia ice in the belts and the Great Red Spot, and poorly characterised by a real refractive index of 1.6 or greater. This may be the result of ammonia cloud at higher altitude obscuring a deeper cloud layer of unknown composition., 14 figures + 4 tables, preprint accepted by Icarus on the 29th of November 2019

International audience; Using TEXES, the Texas Echelon cross Echelle Spectrograph, mounted on the Gemini North 8-m telescope we have mapped the spatial variation of H 2, CH 4, C 2H 2 and C 2H 6 thermal-infrared emission of Neptune. These high-spectral-resolution, spatially resolved, thermal-infrared observations of Neptune offer a unique glimpse into the state of Neptune's stratosphere in October 2007, LS = 275.4° just past Neptune's southern summer solstice ( LS = 270°). We use observations of the S(1) pure rotational line of molecular hydrogen and a portion of the nu4 band of methane to retrieve detailed information on Neptune's stratospheric vertical and meridional thermal structure. We find global-average temperatures of 163.8 ± 0.8, 155.0 ± 0.9, and 123.8 ± 0.8 K at the 7.0 × 10 -3-, 0.12-, and 2.1-mbar levels with no meridional variations within the errors. We then use the inferred temperatures to model the emission of C 2H 2 and C 2H 6 in order to derive stratospheric volume mixing ratios (hence forth, VMR) as a function of pressure and latitude. There is a subtle meridional variation of the C 2H 2 VMR at the 0.5-mbar level with the peak abundance found at -28° latitude, falling off to the north and south. However, the observations are consistent within error to a meridionally constant C 2H 2 VMR of 3.3-0.9+1.2×10-8 at 0.5 mbar. We find that the VMR of C 2H 6 at 1-mbar peaks at the equator and falls by a factor of 1.6 at -70° latitude. However, a meridionally constant VMR of 9.3-2.6+3.5×10-7 at the 1-mbar level for C 2H 6 is also statistically consistent with the retrievals. Temperature predictions from a radiative-seasonal climate model of Neptune that assumes the hydrocarbon abundances inferred in this paper are lower than the measured temperatures by 40 K at 7 × 10 -3 mbar, 30 K at 0.12 mbar and 25 K at 2.1 mbar. The radiative-seasonal model also predicts meridional temperature variations on the order of 10 K from equator to pole, which are not observed. Assuming higher stratospheric CH 4 abundance at the equator relative to the south pole would bring the meridional trends of the inferred temperatures and radiative-seasonal model into closer agreement. We have also retrieved observations of C 2H 4 emission from Neptune's stratosphere using TEXES on the NASA Infrared Telescope Facility (IRTF) in June 2003, LS = 266°. Using the observations from the middle of the planet and an average of the middle three latitude temperature profiles from the 2007 observations (9.5° of LS later, the seasonal equivalent of 9.5 Earth days within Earth's seasonal cycle), we infer a C 2H 4 VMR of 5.9-0.8+1.0×10-7 at 1.5 × 10 -3 mbar, a value that is 3.25 times that predicted by global-average photochemical models.

Within several days of A. Wesley’s announcement that Jupiter was hit by an object on UT 19 July 2009, we observed the impact site with (1) the Hubble Space Telescope (HST) at UV through visible (225–924 nm) wavelengths, (2) the 10-m W.M. Keck II telescope in the near-infrared (1–5 μm), and (3) the 8-m Gemini-North telescope in the mid-infrared (7.7–18 μm). All observations reported here were obtained between 22 and 25 July 2009. Observations at visible and near-infrared wavelengths show that large (∼0.75-μm radius) dark (imaginary index of refraction m i ∼ 0.01–0.1) particulates were deposited at atmospheric pressures between 10 and 200–300 mbar; analysis of HST-UV data reveals that in addition smaller-sized (∼0.1 μm radius) material must have been deposited at the highest altitudes (∼10 mbar). Differences in morphology between the UV and visible/near-IR images suggest three-dimensional variations in particle size and density across the impact site, which probably were induced during the explosion and associated events. At mid-infrared wavelengths the brightness temperature increased due to both an enhancement in the stratospheric NH 3 gas abundance and the physical temperature of the atmosphere. This high brightness temperature coincides with the center part of the impact site as seen with HST. This observation, combined with (published) numerical simulations of the Shoemaker-Levy 9 impacts on Jupiter and the Tunguska airburst on Earth, suggests that the downward jet from the terminal explosion probably penetrated down to the ∼700-mbar level.

The global distribution of phosphine (PH3) on Jupiter and Saturn is derived using 2.5 cm-1 spectral resolution Cassini/CIRS observations. We extend the preliminary PH3 analyses on the gas giants [Irwin, P.G.J., and 6 colleagues, 2004. Icarus 172, 37-49; Fletcher, L.N., and 9 colleagues, 2007a. Icarus 188, 72-88] by (a) incorporating a wider range of Cassini/CIRS datasets and by considering a broader spectral range; (b) direct incorporation of thermal infrared opacities due to tropospheric aerosols and (c) using a common retrieval algorithm and spectroscopic line database to allow direct comparison between these two gas giants. The results suggest striking similarities between the tropospheric dynamics in the 100-1000 mbar regions of the giant planets: both demonstrate enhanced PH3 at the equator, depletion over neighbouring equatorial belts and mid-latitude belt/zone structures. Saturn's polar PH3 shows depletion within the hot cyclonic polar vortices. Jovian aerosol distributions are consistent with previous independent studies, and on Saturn we demonstrate that CIRS spectra are most consistent with a haze in the 100-400 mbar range with a mean optical depth of 0.1 at 10 μm. Unlike Jupiter, Saturn's tropospheric haze shows a hemispherical asymmetry, being more opaque in the southern summer hemisphere than in the north. Thermal-IR haze opacity is not enhanced at Saturn's equator as it is on Jupiter. Small-scale perturbations to the mean PH3 abundance are discussed both in terms of a model of meridional overturning and parameterisation as eddy mixing. The large-scale structure of the PH3 distributions is likely to be related to changes in the photochemical lifetimes and the shielding due to aerosol opacities. On Saturn, the enhanced summer opacity results in shielding and extended photochemical lifetimes for PH3, permitting elevated PH3 levels over Saturn's summer hemisphere. © 2009 Elsevier Inc.

High spectral resolution observations from the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169–297] are analysed to derive new estimates for the mole fractions of CH4, CH3D and 13CH4 of ( 4.7 ± 0.2 ) × 10 −3 , ( 3.0 ± 0.2 ) × 10 −7 and ( 5.1 ± 0.2 ) × 10 −5 respectively. The mole fractions show no hemispherical asymmetries or latitudinal variability. The analysis combines data from the far-IR methane rotational lines and the mid-IR features of methane and its isotopologues, using both the correlated-k retrieval algorithm of Irwin et al. [Irwin, P., and 9 colleagues, 2008. J. Quant. Spectrosc. Radiat. Trans. 109, 1136–1150] and a line-by-line approach to evaluate the reliability of the retrieved quantities. C/H was found to be enhanced by 10.9 ± 0.5 times the solar composition of Grevesse et al. [Grevesse, N., Asplund, M., Sauval, A., 2007. Space Sci. Rev. 130 (1), 105–114], 2.25 ± 0.55 times larger than the enrichment on Jupiter, and supporting the increasing fractional core mass with distance from the Sun predicted by the core accretion model of planetary formation. A comparison of the jovian and saturnian C/N, C/S and C/P ratios suggests different reservoirs of the trapped volatiles in a primordial solar nebula whose composition varies with distance from the Sun. This is supported by our derived D/H ratio in methane of ( 1.6 ± 0.2 ) × 10 −5 , which appears to be smaller than the jovian value of Lellouch et al. [Lellouch, E., Bezard, B., Fouchet, T., Feuchtgruber, H., Encrenaz, T., de Graauw, T., 2001. Astron. Astrophys. 370, 610–622]. Mid-IR emission features provided an estimate of C 12 / C 13 = 91.8 −7.8 +8.4 , which is consistent with both the terrestrial ratio and jovian ratio, suggesting that carbon was accreted from a shared reservoir for all of the planets.

We present the first spectra of Neptune taken with the Spitzer Space Telescope, highlighting the high-sensitivity, moderate-resolution 10–20 μm (500–1000 cm^(−1)) spectra. We report the discovery of methylacetylene (CH_3C_2H) and diacetylene (C_4H_2) with derived 0.1-mbar volume mixing ratios of (1.2±0.1)×10^(−10) and (3 ±1)×10^(−12) respectively.

The J = 3–2 rotational line of CO in Neptune has been measured using the heterodyne receiver B3 at the JCMT. The spectral resolution was 1.25 MHz and 25 tunings were used to cover a frequency range of almost 20 GHz. The measured line shape, encompassing both the broad absorption feature arising in the lower atmosphere and a narrow emission core from the upper stratosphere, indicates that the CO mole ratio is not uniform with altitude, with best-fit values of 2.2 −0.4 +0.6 × 10 −6 in the upper stratosphere and 0.6 ± 0.4 × 10 −6 in the lower stratosphere and troposphere. The higher stratospheric abundance indicates that a dual, internal and external, origin of CO is most likely.

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° S planetographic latitude) to 7.7 years (troposphere, 97% confidence at 6° 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° N to 20° S latitude over the 1994–2000 time period. Oscillations with a period of 4.5 years are found near 7°–8° 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° S.

Jupiter's remaining White Oval changed color in late 2005 and became noticeably red in early 2006, as reported by amateur observers. We present wind and color analyses from high spatial resolution images taken with the Hubble Space Telescope Advanced Camera for Surveys in April 2006. These images suggest that the recent color change was tied to a strengthening of this storm, as implied by increased vorticity, causing it to become more like the Great Red Spot. From a historical perspective, the current activity may be consistent with the generation of new anticyclones at this latitude in the coming months and years.

Ethane (C 2 H 6 ), methylacetylene (CH 3 C 2 H or C 3 H 4 ) and diacetylene (C 4 H 2 ) have been discovered in Spitzer 10–20 μm spectra of Uranus, with 0.1-mbar volume mixing ratios of ( 1.0 ± 0.1 ) × 10 −8 , ( 2.5 ± 0.3 ) × 10 −10 , and ( 1.6 ± 0.2 ) × 10 −10 , respectively. These hydrocarbons complement previously detected methane (CH 4 ) and acetylene (C 2 H 2 ). Carbon dioxide (CO 2 ) was also detected at the 7 - σ level with a 0.1-mbar volume mixing ratio of ( 4 ± 0.5 ) × 10 −11 . Although the reactions producing hydrocarbons in the atmospheres of giant planets start from radicals, the methyl radical (CH 3 ) was not found in the spectra, implying much lower abundances than in the atmospheres of Saturn or Neptune where it has been detected. This finding underlines the fact that Uranus' atmosphere occupies a special position among the giant planets, and our results shed light on the chemical reactions happening in the absence of a substantial internal energy source.

Retrievals run on Cassini Composite Infrared Spectrometer data obtained during the distant Jupiter flyby have been used to generate global temperature maps of the planet in the troposphere and stratosphere. Similar retrievals were performed on Voyager 1 IRIS data and have provided the first detailed IRIS map of the stratosphere. In both data sets, high latitude troposphere temperatures are presented for the first time, and the meridional gradients indicate the presence of circumpolar jets. Thermal winds were calculated for each data set and show strong vertical shears in the zonal winds at low latitudes. 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). 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, Friedson 1999). 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 time scales. 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.

Neptune was observed by the Infrared Space Observatory (ISO) Long-Wavelength Spectrometer (LWS) between 46 and 185 μm. At wavelengths between 50 and 110 μm the accuracy of these measurements is ⩽0.3 K. Observations of this planet made by the ISO Short-Wavelength Spectrometer between 28 and 44 μm were combined with the LWS data to determine a disk-averaged temperature profile and derive several physical quantities. The combined spectra are matched best by a He/(H2+He) mass ratio of 26.4+2.6−3.5%, reflecting a He molar fraction of 14.9+1.7−2.2%, assuming the molar fraction of CH4 to be 2% in the troposphere. This He abundance is consistent with one derived from analysis of joint Voyager-2 IRIS and radio occultation experiment data, a technique whose accuracy has recently been called into question. For a disk average, the para-H2 fraction is found to be no more than ∼1.5% different from its equilibrium value, and the N2 mixing ratio is probably less than 0.7%. The composite spectrum is best fit by invoking a CH4 ice condensate cloud. Using a Mie approximation to particle scattering and absorption, best-fit particle sizes lie between 15 and 40 μm. The composite spectra are relatively insensitive to the vertical distribution of the cloud, but the particle scale height must be greater than 5% of the gas scale height. The best models are consistent with an effective temperature for Neptune that is 59.5±0.6 K, a value slightly lower than derived by the Voyager IRIS experiment—possibly Neptune's mid- and far-infrared emission has changed during the seven years that lie between its encounter with Voyager 2 and the first spectra taken of this planet with ISO. The model spectra are also ostensibly lower than ground-based observations in the spectral range of 17–24 μm, but this discrepancy can be relieved by perturbing the temperature of the lower stratosphere where the LWS spectrum is not particularly sensitive, combined with the uncertainty in the absolute calibration of the ground-based measurements.

Imaging and spectroscopy of Neptune's thermal infrared emission is used to assess seasonal changes in Neptune's zonal mean temperatures between Voyager-2 observations (1989, heliocentric longitude Ls=236) and southern summer solstice (2005, Ls=270). Our aim was to analyse imaging and spectroscopy from multiple different sources using a single self-consistent radiative-transfer model to assess the magnitude of seasonal variability. Globally-averaged stratospheric temperatures measured from methane emission tend towards a quasi-isothermal structure (158-164 K) above the 0.1-mbar level, and are found to be consistent with spacecraft observations of AKARI. This remarkable consistency, despite very different observing conditions, suggests that stratospheric temporal variability, if present, is $\pm$5 K at 1 mbar and $\pm$3 K at 0.1 mbar during this solstice period. Conversely, ethane emission is highly variable, with abundance determinations varying by more than a factor of two. The retrieved C2H6 abundances are extremely sensitive to the details of the T(p) derivation. Stratospheric temperatures and ethane are found to be latitudinally uniform away from the south pole (assuming a latitudinally-uniform distribution of stratospheric methane). At low and midlatitudes, comparisons of synthetic Voyager-era images with solstice-era observations suggest that tropospheric zonal temperatures are unchanged since the Voyager 2 encounter, with cool mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25-50 {\mu}m mapping of tropospheric temperatures and para-hydrogen disequilibrium suggests a symmetric meridional circulation with cold air rising at mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the equator and poles (super-equilibrium para-H2 conditions). The most significant atmospheric changes are associated with the polar vortex (absent in 1989)., Comment: 35 pages, 19 figures. Accepted for publication in Icarus

We used the InfraRed Imaging Spectrometer (IRIS) on the Anglo-Australian Telescope to monitor the impacts of Comet Shoemaker-Levy 9 with Jupiter.

New 5.2-μm thermal images of Saturn's clouds reveal a strong axisymmetric banded structure centered at 45°S with discrete cold spots about 30,000–50,000 km long that: (i) lower the ∼180-K brightness temperature by 8–10 K; (ii) rotate at a rate that is consistent with cloud-tracked zonal winds; and (iii) exhibit no correlation with structures seen in reflected sunlight. They are explained by variations of optical thickness of clouds just below the 1-bar level.

On 13–14 August 1996, we carried out the first coordinated contemporaneous imaging of Neptune, using the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 and the NASA Infrared Telescope Facility (IRTF) NSFCAM InSb camera to obtain high spatial resolution absolutely calibrated imagery at wavelengths from 0.2 to 2.5 μm. We used nine HST orbits to provide unique dynamical coverage of a single rotation of Neptune. During three orbits we obtained virtually simultaneous groundbased images. These data provide an extended range of wavelengths that sample the Rayleigh scattering regime, both strong and weak methane bands, and strong near-infrared hydrogen collision-induced opacity bands, from which strong constraints can be obtained on the properties of Neptune's cloud features. We developed very precise navigation techniques, which were required to achieve colocation of the observations from these different observatories. Technique advances include compensating for limb profile distortions by bright cloud features in HST images and dealing with a nearly invisible limb in the near-IR groundbased images. We achieved RMS center-finding accuracy of 0.003′′–0.006′′ (0.05–0.1 pixels) for HST navigations. To obtain the subpixel navigation accuracy of the groundbased images, we determined NSFCAM pixel scale versus wavelength and as a function of location on the detector, establishing a distortion correction equation for NSFCAM imaging. This permitted use of a navigation method based on offsetting from Triton, with which we achieved IRTF center-finding accuracy of 0.02′′ (0.1 pixel) RMS, and 0.2–0.3 pixels absolute. We developed a novel differential deconvolution method for significantly reducing deconvolution artifacts within the planetary disk and improving convergence properties for planetary cloud features, resulting in by far the most detailed groundbased images of Neptune yet obtained without speckle imaging or adaptive optics.

A series of far infrared (FIR) spectra of Mars between 43 and 196 μm was taken with the Long Wavelength Spectrometer (LWS) on board the European Space Agency's Infrared Space Observatory (ISO). Analysis of these medium-resolution data reveals a rotational modulation of the disk-averaged FIR brightness temperature. The observed variability of ±1.5% in the LWS wavelength range compares favorably with the predictions of a thermophysical model of the martian surface. A surface emissivity of ∼0.90 gives good agreement between the measured and the modeled brightness temperatures and leads to an improved estimate of the LWS photometric calibration uncertainty.

During the first six orbits of the Galileo spacecraft's prime mission, the Solid State Imaging (SSI) system acquired multispectral image mosaics of Jupiter's Great Red Spot, an equatorial belt/zone boundary, a “5-μm hot spot” similar to the Galileo Probe entry site, and two of the classic White Ovals. We present mosaics of each region, approximating their appearance at visible wavelengths and showing cloud height and opacity variations. The local wind field is derived by tracking cloud motions between multiple observations of each region with time separations of roughly 1 and 10 hr. Vertical cloud structure is derived in a companion paper by Banfieldet al. (Icarus135, 230–250). Galileo's brief, high-resolution observations complement Earth-based and Voyager studies and offer local meteorological context for the Galileo Probe results. Our results show that the dynamics of the zonal jets and large vortices have changed little since Voyager, with a few exceptions. We detect a cyclonic current within the center of the predominantly anticyclonic Great Red Spot. The zonal velocity difference between 0° S and 6° S has increased by 20 m sec^(−1). We measure a strong northeast flow approaching the hot spot. This flow indicates either massive horizontal convergence or the presence of a large anticyclonic vortex southeast of the hot spot. The current compact arrangement of two White Ovals and a cyclonic structure greatly perturbs the zonal jets in that region.

We present high-resolution 8–14 μm observations of Shoemaker–Levy 9 sites conducted on July 20, 30, and 31 1994 UT at the NASA Infrared Telescope Facility. Stratospheric heating was detected from strong enhancements of methane emission near 8.1 μm over areas at least 15,000 km wide around the K site observed 23 hr after impact and around the L site 11 hr after impact. The intensity distribution between strong and weaker CH4lines implies that the stratospheric heating was primarily confined to pressures less than 500 μbar. The L site temperature increased by 80 ± 10 K at 5 μbar, but did not exceed 20 K around 1 mbar or 10 K around 10 mbar. The older K site was still 30 ± 5 K warmer than the surroundings at the 10-μbar level. The excess thermal energy stored in the upper jovian stratosphere was 3+3−1.5× 1026erg over the L site, and 2+2−1× 1026erg over the K site at the time of the observations. Comparison with numerical simulations indicates that a large fraction (>20%) of the kinetic energy of the L plume was transferred to the jovian atmosphere and not immediately radiated away. Acetylene line emission near 13.4 μm was enhanced over an area ∼18,000 km wide centered on the E site 2.6 days after impact. Radiative transfer models of this emission indicate temperatures 37 ± 7 K higher than nominal around 3 μbar. No such enhancement was seen in CH4spectral images, implying that the temperature perturbation did not significantly extend below the ∼20-μbar level. The H site observed simultaneously was 12 ± 5 K warmer than the surroundings 1.4 day after impact. C2H2lines were still slightly more intense over the K + W and Q1 sites on July 30 and 31, 8 to 10 days after impact. These observations can be interpreted either by temperature differences of about 13 and 10 K respectively in the 3-μbar region, or by an increase in the C2H2column density of 2.5–5 × 1017molecule cm−2. Emission from hydrogen cyanide lines around 13.4 μm was detected over all sites observed. The mass of HCN is about 2 × 1012g for the biggest plumes (K, L, G), 0.95 ± 0.5 × 1012g over the E site, and 0.45 ± 0.2 × 1012g over the H site. The total mass of HCN produced by all fragments is estimated to be 1.1 ± 0.4 × 1013g. A consistent interpretation of the different pieces of information available suggests that the H $cl10$plume was richer in dust than the E or A plume.

In recent years there has been significant progress in theab initiocomputation and modeling of the collision-induced absorption in H2–H2and H2–He pairs in the rotovibrational and purely rototranslational bands covering 0–6000 cm−1at temperatures from 40 to 300 K. Extensive experimental and theoretical results have been obtained in a number of laboratories regarding this absorption as a function of frequency and temperature. This report summarizes the most advanced literature on this subject and presents a number of new results. Moreover, this report is designed to facilitate the utilization of this knowledge for the study of planetary atmospheres, and for future research of the H2–H2and H2–He infrared spectra. The theoretical absorption coefficients arising from free-free transitions in collisional pairs are available in the form of Fortranprograms which permit rapid and reliable evaluation of spectral intensities even for frequencies and temperatures at which laboratory measurements do not exist. The various approximations affecting the accuracy of the theory applied here are discussed in some detail. The theoretical spectra closely duplicate the existing laboratory measurements of collision-induced absorption, whose accuracy is discussed; only for the case of the fundamental band of H2–He are there small discrepancies from recent measurements which exceed somewhat the combined uncertainties of theory and measurement. The simple analytical functions on which these computer programs are based have also been compared with the quantum mechanical computations of the spectra and very close agreement has been observed. Notes regarding the use of the computer programs and sample outputs are given to serve as a test for their applications.

Infrared spectra of Jupiter's atmosphere were obtained with the infrared spectrometer (IRS) on the 1.5-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) during the first 2 days of the impacts of the fragments of Comet Shoemaker–Levy 9 (1993e). We monitored 3.51 ± 0.17 μm radiation from the impact areas, undisturbed areas, and auroral regions of Jupiter after the A and E impacts. The strong emission of a portion of the P-branch of the ν3band of CH4was detected on the A impact area 4 hr after the impact. H+3emissions are found to be decreased at the A and E impact sites after 4 hr and 10 hr 50 min of the impacts, respectively, compared with undisturbed areas at the same latitude. The temperatures of the southern H+3aurora were normal within the first several hours following the A and E impacts.

The impact of fragments of Comet Shoemaker-Levy 9 on Jupiter and the resulting vapor plume expansion are investigated by conducting three-dimensional numerical simulations using the smoothed particle hydrodynamics (SPH) method. An icy body, representing the cometary fragments, with a velocity of 60 km/sec and a diameter of 2 km can penetrate to 350 km below the 1-bar pressure level in the atmosphere. Most of the initial kinetic energy of the fragment is transferred to the atmosphere between 50 km and 300 km below the 1-bar pressure level. The shock-heated atmospheric gas in the wake is totally dissociated and partially ionized. Scaling our SPH results to other sizes indicates that fragments larger than ∼100 m in diameter can penetrate to below the visible cloud decks. The energy deposited in the atmosphere is explosively released in the upward expansion of the resulting plume. The plume preferentially expands upward rather than horizontally due to the density gradient of the ambient atmosphere. It rises ≥10^2 km in ∼10^2 sec. Eventually the total atmospheric mass ejected to above 1 bar is ≥40 times the initial mass of the impactor. The plume temperature at a radius ∼10^3 km is >10^3 K for 10^3 sec for a 2-km fragment. We predict that impact-induced plumes will be observable with the remote sensing instruments of the Galileo spacecraft. As the impact site rotates into the view of Earth some 20 min after the impact, the plume expansion will be observable using the Hubble Space Telescope and from visible and infrared instruments on groundbased telescopes. The rising plume reaches ∼3000 km altitude in ∼10 min and will be visible from Earth.

We present new photometric measurements of Uranus and Neptune between 0.35 and 2.0 mm. Together with our previous results (Orton et al., 1986, Icarus 67, 289-304), these data have allowed us to determine their near-millimeter brightness temperatures with improved accuracy. Both planets exhibit smoothly varying continuum spectra in this wavelength region, with no evidence of strong unresolved spectral structure which could be attributed to particular molecular transitions. The possible depression in the Uranian spectrum at 1.3 mm noted by Orton et al. is not confirmed by the new measurements. Combining the two data sets, and using Mars as the primary flux standard, we derive the following empirical fit to the Uranian temperature spectrum, TU(λ), in the 0.35-3.3-mm region:TU = ao + a1 [Log10(λ)] + a2 [Log10(λ)]2 + a3 [Log10(λ)]3K, withao = -795.694 a1 = 845.179 a2 = -288.946 a3 = 35.200λ = wavelengthinmicrometers. We have also measured very accurately the surface brightness ratio of Neptune with respect to Uranus over the same wavelength range. The ratio is remarkably constant, implying that the tropospheres of these planets are very similar in the 1-4-bar regions. The observations are consistent with a wavelength-independent Neptune: Uranus brightness ratio of 0.94, although the possibility of a slightly lower value near 0.8 mm, due to CO absorption of Neptune, cannot be ruled out. The neptunian brightness temperature, TN(λ), between 0.35 and 3.3 mm is given byTN = ao + [Log10(λ)] + a2 [Log10(λ)]2 + a3 [Log10(λ)]3K, withao = -598.901 a1 = 655.681 a2 = -229.545 a3 = 28.994 λ = wavelengthinmicrometers. We estimate the internal errors in temperatures derived from these fits to be less than 2 K, and the absolute calibration error arising from uncertainty in the martian temperature to be 5%.

NASA-IRTF observations of Neptune's disk-averaged spectrum are presently used, in conjunction with a lower-resolution spectrum, to furnish a more reliable absolute intensity calibration of portions of Neptune's disk-averaged spectrum. The temperature profile adopted is consistent with the size and shape of the H2 J = 3-1 quadrupole feature detected in the emission. High-resolution measurements of (C-13C-12)H6 and (C-12)2H6 imply C-12/C-13 of 78 +/- 26; this is consistent with solar and telluric values.

Past observations of Neptune's 7- to 14-μm spectrum showed emission from methane and ethane, and suggested variation in the strength of the ethane emission. We demonstrate that the ratio of ethane emission to methane emission increased between 1985 and 1991 by a factor of 1.47 ± 0.11. The data indicate that the 12.2-μm ethane feature, rather than the 7.7-μm methane feature, is responsible for most of the change. The observed variation is likely caused by either a nonuniform increase in the stratospheric temperature or more probably an increase in the ethane concentration by 15% or more.

An independent measure of the absolute brightness of the disk-averaged spectrum measured by Orton et al. (1987) is attempted via observations of Uranus and Neptune at discrete wavelengths between 8.17 and 13.0 microns. These observations are found to be consistent with the suggested upward recalibrations of the Uranus and Neptune spectra by factors of 1.6 and 1.12, respectively. Both graphic and tabular results are presented.

International audience; We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft during the Titan flybys T0-T10 (July 2004-January 2006). The spectra characterize various regions on Titan from 70° S to 70° N with a variety of emission angles. We study the molecular signatures observed in the mid-infrared CIRS detector arrays (FP3 and FP4, covering roughly the 600-1500 cm -1 spectral range with apodized resolutions of 2.54 or 0.53 cm -1). The composite spectrum shows several molecular signatures: hydrocarbons, nitriles and CO 2. A firm detection of benzene (C 6H 6) is provided by CIRS at levels of about 3.5×10 around 70° N. We have used temperature profiles retrieved from the inversion of the emission observed in the methane nu band at 1304 cm -1 and a line-by-line radiative transfer code to infer the abundances of the trace constituents and some of their isotopes in Titan's stratosphere. No longitudinal variations were found for these gases. Little or no change is observed generally in their abundances from the south to the equator. On the other hand, meridional variations retrieved for these trace constituents from the equator to the North ranged from almost zero (no or very little meridional variations) for C 2H 2, C 2H 6, C 3H 8, C 2H 4 and CO 2 to a significant enhancement at high northern (early winter) latitudes for HCN, HC 3N, C 4H 2, C 3H 4 and C 6H 6. For the more important increases in the northern latitudes, the transition occurs roughly between 30 and 50 degrees north latitude, depending on the molecule. Note however that the very high-northern latitude results from tours TB-T10 bear large uncertainties due to few available data and problems with latitude smearing effects. The observed variations are consistent with some, but not all, of the predictions from dynamical-photochemical models. Constraints are set on the vertical distribution of C 2H 2, found to be compatible with 2-D equatorial predictions by global circulation models. The D/H ratio in the methane on Titan has been determined from the CH 3D band at 1156 cm -1 and found to be 1.17-0.28+0.23×10. Implications of this deuterium enrichment, with respect to the protosolar abundance on the origin of Titan, are discussed. We compare our results with values retrieved by Voyager IRIS observations taken in 1980, as well as with more recent (1997) disk-averaged Infrared Space Observatory (ISO) results and with the latest Cassini-Huygens inferences from other instruments in an attempt to better comprehend the physical phenomena on Titan.

Far-infrared Fourier-transform spectrometer measurements of the 1-0 and 3-2 PH3 transitions in Saturn's disk near 267 and 800 GHz (8.9 and 26.7/cm), respectively, were analyzed simultaneously to derive a global mean profile for the PH3 vertical mixing ratio between 100 and 600 mbar total pressure. The far-infrared spectrum is relatively free from spectral interlopers, suffers minimal absorption or scattering by atmospheric particulates, and contains intrinsically weak PH3 lines that are sensitive to a range of atmospheric depths. The combined spectra are inconsistent with a uniform tropospheric mixing ratio, even with a stratospheric cut-off. They are consistent with a volume mixing ratio of PH3 that drops from 1.2 x 10(exp -5) at 645 mbar pressure to a value of 4.1 x 10(exp -7) at 150 mbar pressure, a decrease that is linear is log abundance vs log pressure. The mixing ratio could drop even more quickly at atmospheric pressures below 150 mbar and still be consistent with the data. The mixing ratio may well remain constant with depth for pressures above 630 mbar. The maximum PH3 mixing ratio in this model is consistent with a [P]/[H] ratio in the deep atmosphere that is about a factor of 10 higher than solar composition. Such a model is consistent with rapid mixing up to the radiative-convective boundary and transport by, for example, vertical waves just above this boundary. In the best fitting model, the eddy diffusion coefficient is approximately 10(exp 4) sq cm near 630 mbar, and it must increase with altitude. The predominant PH3 loss mechanisms are direct photolysis by UV radiation and scavenging by H atoms produced by the photolysis.

The presence of a temperature inversion in the lower stratospheres of both Uranus and Neptune is confirmed by the 20-micron photometric data presented. It is found that the brightness temperature difference between 17.8 and 19.6 microns is 0.8 + or - 0.5 K for Uranus and 1.8 + or - 0.6 K for Neptune, implying that the temperature inversions of both planets are weaker than previously thought. Comparisons with model atmospheres suggested by Appleby (1980) imply that these temperature inversions may be understood as a consequence of heating through CH4 and aerosol absorption of sunlight. The stratospheric CH4 mixing ratio of Neptune must, however, be higher than that at the temperature minimum.

Spectra from the Voyager 1 IRIS experiment confirm the existence of enhanced infrared emission near Jupiter's north magnetic pole in March 1979. The spectral characteristics of the enhanced emission are consistent with a Planck source function. A temperature-pressure profile is derived for the region near the north magnetic pole, from which quantitative abundance estimates of minor species are made. Some species previously detected on Jupiter, including CH3D, C2H2, and C2H6, have been observed again near the pole. Newly discovered species, not previously observed on Jupiter, include C2H4, C3H4, and C6H6. All of these species except CH3D appear to have enhanced abundances at the north polar region with respect to midlatitudes. Upper limits are determined for C4H2 and C3H8. The quantitative results are compared with model calculations based on ultraviolet results from the IUE satellite. The plausibility of the C6H6 identification is discussed in terms of the literature on C2H2 polymerization. The relation of C6H6 to cuprene is also discussed.

It is possible for large particles of NH3 ice to explain two phenomena associated with observations of thermal infrared emission from the atmosphere of Saturn: (1) the depression of thermal brightness near the equator, which is coincident with a visibly bright zone-like region, and (2) some disagreements between infrared and radio occultation results. Particles of NH3 ice can provide the requisite opacity to explain the contrast between the equatorial region and the brighter area near 15°S for Pioneer Saturn Infrared Radiometer 45-μm channel data. NH3 ice particle clouds can also reconcile the 45-μm brightness of both regions (near the equator and near 15°S) with the mean temperatures structure of the Voyager 2 radio occultation results. A cloud model with ice particles distributed in equal ratio with gas particles up to the 100-mbar pressure level best fits the equatorial data; a thinner cloud or one which does not extend higher than the 400-mbar limit of the convective region best matches data for the 15°S region. At 20 μm, however, the radio occultation temperature structure predicts brightnesses which are lower than those observed for both regions, and it could indicate the possibility that another source of opacity which is latitudinally variable exists in the stratosphere.

The thermal infrared maps of Venus published by Murray, Wildey, and Westphal (1963) and Westphal, Wildey, and Murray (1965) have been analyzed systematically in order to separate the observed intensity into a limb-darkening component and a solar-associated component representing fixed patterns of intensity corotating with the earth and sun, respectively. Interesting new results are obtained for the solar-associated component. Regions near the subsolar point and the poles are not covered in the original maps or in the analysis. The solar-associated pattern of intensity is very nearly symmetric about the equator. In both northern and southern hemispheres, an intensity minimum seems to occur near the morning terminator at middle to high latitudes, slightly beyond the limit of the maps. An intensity maximum occurs on the equator slightly to the east of the antisolar point. Three broad ridges of relatively high intensity radiate away from this point, one pointing to the west along the equator, the others pointing to the northeast and southeast, respectively. The eastward tilt of the latter two ridges may indicate that horizontal exchange is important in maintaining the equatorial maximum of zonal momentum which is associated with the 4-day circulation of the Venus atmosphere.

Observational determinations of the absolute spectral reflectivities of visually distinct regions of Jupiter are presented. The observations cover the 3390–8400 A region at 10 A resolution, and they are compared with observations using 150–200 A filters in the 3400–6400 A range. The effective reflectivities for several regions (on the meridian) in the 3400–8400 A range are: South Tropical Zone, 0.76±0.05; North Tropical Zone, 0.68±0.08; South Equatorial Belt, 0.63±0.08; North Equatorial Belt, 0.62±0.04; and the Great Red Spot, 0.64±0.09. Reflectivities near the limb are also observed. The appropriate blue and red reflectivities are tabulated in support of the Pioneer 10 and 11 imaging photopolarimeter experiments. For the regions listed above, equivalent widths of molecular bands vary as: CH 4 (6190 A), 14–16 A; CH 4 (7250 A), 77–86 A; and NH 3 (7900 A), 87–95 A. Significant differences from the results of C. B. Pilcher, R. G. Prinn, and T. B. McCord (“Spectroscopy of Jupiter: 3200 to 11200 A,” J. Atmos. Sci. 30 , 302–307.)

We examine the effects of NH 3 ice particle clouds in the atmosphere of Jupiter on outgoing thermal radiances. The cloud models are characterized by a number density at the cloud base, by the ratio of the scale height of the vertical distribution of particles ( H p ) to the gas scale height ( H g ), and by an effective particle radius. NH 3 ice particle-scattering properties are scaled from laboratory measurements. The number density for the various particle radius and scale height models is inferred from the observed disk average radiance at 246 cm −1 , and preliminary lower limits on particle sizes are inferred from the lack of apparent NH 3 absorption features in the observed spectral radiances as well as the observed minimum flux near 2100 cm −1 . We find lower limits on the particle size of 3 μm if H p / H g = 0.15, or 10 μ mif H p / H g = 0.50 or 0.05. NH 3 ice particles are relatively dark near the far-infrared and 8.5-μm atmospheric windows, and the outgoing thermal radiances are not very sensitive to various assumptions about the particle-scattering function as opposed to radiances at 5 μm, where particles are relatively brighter. We examined observations in these three different spectral window regions which provide, in principle, complementary constraints on cloud parameters. Characterization of the cloud scale height is difficult, but a promising approach is the examination of radiances and their center-to-limb variation in spectral regions where there is significant opacity provided by gases of known vertical distribution. A blackbody cloud top model can reduce systematic errors due to clouds in temperature sounding to the level of 1K or less. The NH 3 clouds provide a substantial influence on the internal infrared flux field near the 600-mbar level.

Observations of Jovian limb structure at 8.11 and 8.45 microns are reported. These are used along with other limb structure and spectral data in the 8-14 micron region to derive a model of the thermal and cloud structure within the 1.0-0.01 bar pressure regime. The temperature is about 165 K at 1.00 bar, 108 K at 0.10 bar, and 143 K at 0.03 bar. In zones, an optically opaque cloud of NH3 exists near the 143 K (0.60 bar) level. A partly transparent haze of solid NH3 particles overlies the cloud. Belts are free of the cloud and have a much lower abundance of NH3 haze than the zones. The data are consistent with an NH3 gas abundance defined by saturation equilibrium, with a mixing ratio of 0.00015 deep in the atmosphere, and with a CH4 mixing ratio of 0.002, about three times the currently accepted value.

An effort has been made to ascertain how particle shape and composition affect the strength and shape of resonant absorption features at 9.4 and 26 microns. A shifting of the peak of the resonance relative to that for spherical particles is noted in the computational results obtained for the extinction cross-sections of 0.5- and 1-micron, volume-equivalent radius tetrahedral NH3 ice crystals that either possessed or lacked foreign cores. It it judged unlikely that small, (less than 5-micron) NH3 particles could be the principal component of the haze in the 300-500 mbar region of Jupiter.

Temperature profiles for low latitude regions of Jupiter in the 1.0-0.1 bar pressure regime are recovered from Pioneer 10 infrared radiometer data. The temperature near 0.1 bar is 108-117 K, depending on the overlying thermal structure assumed. For the South Equatorial Belt (SEB), the temperature at 1.0 bar is 170 K, assuming an adiabatic lapse rate in the deep atmosphere. The South Tropical Zone temperature at this level is 155 K if pure gaseous absorption is assumed. The temperature is much closer to that in the SEB, assuming the presence of an optically opaque cloud near the 0.6 atm (145 K) level. Such a cloud presence in the STrZ may be correlated with the visible and 5 micron appearance of the planet and with NH3 saturation just below this position. The molar fraction of H2 most consistent with the data is 0.91 + or - 0.08. The effective temperatures of the SEB and STrZ are 127.6 and 124.2 K, respectively. A discrepancy with the preliminary neutral atmosphere inversion of Pioneer 10 radio occultation data remains unexplained.

All of the data acquired at Jupiter by the Infrared Radiometers on board Pioneers 10 and 11 are presented in the form of images with geometric control. The images are compared with 5-μm and visible images taken in the same time frame. The association of dark (blue or brown) and light (white or red) areas with warm and cool areas (at 5, 20, and 45 μm) respectively, extends to nearly all features observed on the planet. Where the normal association of light and dark visible markings with the zonal velocity breaks down (e.g., at the latitude of the South Equatorial Belt during the Pioneer encounters), the infrared emission seems to follow the visible cloud structure rather than the zonal velocity structure. Exceptions to the general rule involve 20-μm radiation, which reflects conditions in the altitude range 0.1–0.3 bar. For example, a comparison between Pioneer 10 and 11 images suggests that the South Equatorial Belt became brighter at 20 μm, but remained constant at other wavelengths between the two encounters.

We report narrowband photometry of the Jovian disk in 10 passbands covering the range from 0.35 to 3.3 mm wavelength. Absolute calibration was referenced to Mars. The derived brightness temperature spectrum is analyzed in the context of existing contraints on the atmospheric temperature structure and composition from ground-based studies at shorter wavelengths and from various spacecraft measurements. Our results for wavelengths between 0.35 and 0.45 mm suggest that the radiances can be matched by models which include NH3 ice particles which are between 30 and 100 μm in size, regardless of the scale height characterizing the cloud. It is difficult however, to model the relatively cool observations longward of 0.7 mm unless additional absorbers are assumed in the atmosphere or a different NH3 lineshape is assumed. If the absolute calibration scale were increased by 5%, the results would be fit by a clear atmosphere (or a small particle cloud) model, with no need to invoke additional absorption in the Jovian atmosphere.

North-to-south scans of Jupiter at 7.8-micron wavelength in early 1981 confirm polar brightening events that correlate with LCM (III), such that a polar limb is bright when the corresponding magnetic pole is tilted earthward. The correlation with magnetic features of the planet suggests that the energy source for the brightenings is magnetospheric particles incident upon the polar regions of the atmosphere. The northern polar events are more prominent and more regular than the southern ones. The polar emission may be indirectly related to the ultraviolet absorber observed near the poles by Voyager 2.

We have made narrowband photometric measurements of Uranus and Neptune covering the wavelength range from 0.35 to 3.3 mm. The observations provide accurate comparative radiometry of these planets. Absolute calibration was referenced to Mars, and to Jupiter as a secondary standard. The results establish Uranus and Neptune as reliable secondary calibrators in their own right. We have combined our observations with other measurements made in the period 1978 through 1984 in the spectral range of 17 μm through 3 mm to form models for atmospheric temperature structure in the vertical range from 100 mbar to 8 bar. The simplest models imply that the tropospheres of both planets are consistent with “frozen” equilibrium H2 and a mixing ratio of CH4 of about 2% by volume in the deep atmosphere. There is some evidence in the Uranus data which implies the presence of discrete spectral lines. These could be due to CH4 pure rotational or dimer transitions or to minor constituents such as CO, which remain uncondensed even at the cold temperatures in the atmosphere of Uranus.

The mean thermal structure of the Jovian atmosphere near the temperature minimum (0.1 bar) is recovered by inversion of thermal radiance data. Improvements over previous studies of this type are made in two respects. (1) Care is taken to select data sources which are on a consistent calibration scale and from a frequency region which minimizes the variance in the recovered temperature. (2) The accuracy in the temperature recovery vs the vertical resolution capability is studied quantitatively. The contributions of various sources of systematic error, which generate significant uncertainty in the recovered thermal structure, are assessed. Sources of systematic error include assumptions about the stratospheric NLTE source function, the extent of cloud cover, the methane mixing ratio, and the calibration scale. Future investigations are outlined which would reduce such uncertainties and provide consistency with a wider range of data on the Jovian upper atmosphere.

Radiometric measurement of Uranus and Neptune near 21 and 32 μm have been made with filters with widths of 8 and 5 μm, respectively. The observations at 21 μm, made on 1985 June 19 at the NASA Infrared telescope facility at Mauna Kea, Hawaii, were calibrated against α Boo and corresponded to brightness temperatures of 54.1 ± 0.3 K for Uranus and 58.1 ± 0.3 K for Neptune. The observations at 32 μm were made on three nights: 1983 May 1 and 1984 May 30 and 31, also at the NASA IRTF. Calibrated against the Jovian satellites Callisto (J4) and Ganymede (J3), these measurements corresponded to brightness temperatures of 51.8 ± 1.5 K for Uranus and 55.6 ± 1.2 K for Neptune. The observations are consistent with higher-resolution studies and confirm the general decrease of brightness temperatures going from about 20 to 30 μm.