17 results on '"Romani, P.N."'
Search Results
2. On the HCN and CO.sub.2 abundance and distribution in Jupiter's stratosphere
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Lellouch, E., Bezard, B., Strobel, D.F., Bjoraker, G.L., Flasar, F.M., and Romani, P.N.
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Jupiter (Planet) -- Properties ,Stratosphere -- Composition ,Atmospheric carbon dioxide -- Distribution ,Planets -- Atmosphere ,Planets -- Properties ,Planets -- Composition ,Company distribution practices ,Astronomy ,Earth sciences - Abstract
To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.05.018 Byline: E. Lellouch (a), B. Bezard (a), D.F. Strobel (b), G.L. Bjoraker (c), F.M. Flasar (c), P.N. Romani (c) Keywords: Jupiter; atmosphere; Atmospheres; dynamics; Atmospheres; composition Abstract: Observations of Jupiter by Cassini/CIRS, acquired during the December 2000 flyby, provide the latitudinal distribution of HCN and CO.sub.2 in Jupiter's stratosphere with unprecedented spatial resolution and coverage. Following up on a preliminary study by Kunde et al. [Kunde, V.G., and 41 colleagues, 2004. Science 305, 1582-1587], the analysis of these observations leads to two unexpected results (i) the total HCN mass in Jupiter's stratosphere in 2000 was (6.0[+ or -]1.5)x10.sup.13g, i.e., at least three times larger than measured immediately after the Shoemaker-Levy 9 (SL9) impacts in July 1994 and (ii) the latitudinal distributions of HCN and CO.sub.2 are strikingly different: while HCN exhibits a maximum at 45[degrees] S and a sharp decrease towards high Southern latitudes, the CO.sub.2 column densities peak over the South Pole. The total CO.sub.2 mass is (2.9[+ or -]1.2)x10.sup.13g. A possible cause for the HCN mass increase is its production from the photolysis of NH.sub.3, although a problem remains because, while millimeter-wave observations clearly indicate that HCN is currently restricted to submillibar ([approximately equal to]0.3mbar) levels, immediate post-impact infrared observations have suggested that most of the ammonia was present in the lower stratosphere near 20 mbar. HCN appears to be a good atmospheric tracer, with negligible chemical losses. Based on 1-dimensional (latitude) transport models, the HCN distribution is best interpreted as resulting from the combination of a sharp decrease (over an order of magnitude in K.sub.yy) of wave-induced eddy mixing poleward of 40[degrees] and an equatorward transport with [approximately equal to]7cms.sup.-1 velocity. The CO.sub.2 distribution was investigated by coupling the transport model with an elementary chemical model, in which CO.sub.2 is produced from the conversion of water originating either from SL9 or from auroral input. The auroral source does not appear adequate to reproduce the CO.sub.2 peak over the South Pole, as required fluxes are unrealistically high and the shape of the CO.sub.2 bulge is not properly matched. In contrast, the CO.sub.2 distribution can be fit by invoking poleward transport with a [approximately equal to]30cms.sup.-1 velocity and vigorous eddy mixing (K.sub.yy=2x10.sup.11cm.sup.2s.sup.-1). While the vertical distribution of CO.sub.2 is not measured, the combined HCN and CO.sub.2 results imply that the two species reside at different stratospheric levels. Comparing with the circulation regimes predicted by earlier radiative-dynamical models of Jupiter's stratosphere, and with inferences from the ethane and acetylene stratospheric latitudinal distribution, we suggest that CO.sub.2 lies in the middle stratosphere near or below the 5-mbar level. Author Affiliation: (a) Observatoire de Paris, F-92195 Meudon, France (b) The Johns Hopkins University, Baltimore, MD 21218, USA (c) NASA/GFSC, Code 693, Greenbelt, MD 20771, USA Article History: Received 14 November 2005; Revised 11 May 2006
- Published
- 2006
3. Titan's atmospheric temperatures, winds, and composition
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Flasar, F.M., Achterberg, R.K., Conrath, B.J., Gierasch, P.J., Kunde, V.G., Nixon, C.A., Bjoraker, G.L., Jennings, D.E., Romani, P.N., Simon-Miller, A.A., Bezard, B., Coustenis, A., Irwin, P.G.J., Teanby, N.A., Brasunas, J., Pearl, J.C., Segura, M.E., Carlson, R.C., Mamoutkine, A., Schinder, P.J., Barucci, A., Courtin, R., Fouchet, T., Gautier, D., Lellouch, E., Marten, A., Prange, R., Vinatier, S., Strobel, D.F., Calcutt, S.B., Read, P.L., Taylor, F.W., Bowles, N., Samuelson, R.E., Orton, G.S., Spilker, L.J., Owen, T.C., Spencer, J.R., Showalter, M.R., Ferrari, C., Abbas, M.M., Raulin, F., Edgington, S., Ade, P., and Wishnow, E.H.
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Cassini (Space probe) -- Usage ,Infrared spectroscopy -- Usage -- Research -- Analysis ,Atmosphere -- Research -- Analysis -- Observations -- Usage ,Earth -- Atmosphere ,Titan (Satellite) -- Research -- Analysis -- Observations -- Usage ,Science and technology - Abstract
Temperatures obtained from early Cassini infrared observations of Titan show a stratopause at an altitude of 310 kilometers (and 186 kelvin at 15°S). Stratospheric temperatures are coldest in the winter northern hemisphere, with zonal winds reaching 160 meters per second. The concentrations of several stratospheric organic compounds are enhanced at mid- and high northern latitudes, and the strong zonal winds may inhibit mixing between these latitudes and the rest of Titan. Above the south pole, temperatures in the stratosphere are 4 to 5 kelvin cooler than at the equator. The stratospheric mole fractions of methane and carbon monoxide are (1.6 ± 0.5) x [10.sup.-2] and (4.5 ± 1.5) x [10.sup.-5] respectively., Unlike other moons in the solar system, Titan has a substantial atmosphere and offers an interesting comparison with Earth and the other planets. Its pressure at the surface is 1.5 [...]
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- 2005
4. Temperatures, winds, and composition in the Saturnian system
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Flasar, F.M., Achterberg, R.K., Conrath, B.J., Pearl, J.C., Bjoraker, G.L., Jennings, D.E., Romani, P.N., Simon-Miller, A.A., Kunde, V.G., Nixon, C.A., Bezard, B., Orton, G.S., Spilker, L.J., Spencer, J.R., Irwin, P.G.J., Teanby, N.A., Owen, T.C., Brasunas, J., Segura, M.E., Carlson, R.C., Mamoutkine, A., Gierasch, P.J., Schinder, P.J., Showalter, M.R., Ferrari, C., Barucci, A., Courtin, R., Coustenis, A., Fouchet, T., Gautier, D., Lellouch, E., Marten, A., Prange, R., Strobel, D.F., Calcutt, S.B., Read, P.L., Taylor, F.W., Bowles, N., Samuelson, R.E., Abbas, M.M., Raulin, F., Ade, P., Edgington, S., Pilorz, S., Wallis, B., and Wishnow, E.H.
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Cassini (Space probe) -- Observations ,Planetary meteorology ,Planets -- Atmosphere ,Saturn (Planet) -- Observations ,Science and technology - Abstract
Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites., Cassini observations of Saturn provide a detailed comparison with Jupiter, successfully studied by Galileo, which will sharpen our ideas about the formation of planetary systems. Each giant, fluid planet has [...]
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- 2005
5. Jupiter's atmospheric composition from the Cassini thermal infrared spectroscopy experiment
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Kunde, V.G., Flasar, F.M., Jennings, D.E., Bezard, B., Strobel, D.F., Conrath, B.J., Nixon, C.A., Bjoraker, G.L., Romani, P.N., Achterberg, R.K., Simon-Miller, A.A., Irwin, P., Brasunas, J.C., Pearl, J.C., Smith, M.D., Orton, G.S., Gierasch, P.J., Spilker, L.J., Carlson, R.C., Mamoutkine, A.A., Calcutt, S.B., Read, P.L., Taylor, F.W., Fouchet, T., Parrish, P., Barucci, A., Courtin, R., Coustenis, A., Gautier, D., Lellouch, E., Marten, A., Prange, R., Biraud, Y., Ferrari, C., Owen, T.C., Abbas, M.M., Samuelson, R.E., Raulin, F., Ade, P., Cesarsky, C.J., Grossman, K.U., and Coradini, A.
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Cassini (Space probe) -- Observations ,Jupiter (Planet) -- Atmosphere -- Chemical properties -- Observations ,Science and technology ,Observations ,Chemical properties - Abstract
The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of acetylene and ethane, the latter a tracer of atmospheric motion; observations of unexpected spatial distributions of carbon dioxide and hydrogen cyanide, both considered to be products of comet Shoemaker-Levy 9 impacts; characterization of the morphology of the auroral infrared hot spot acetylene emission; and a new evaluation of the energetics of the northern auroral infrared hot spot., Jupiter serves as an analog for the numerous extrasolar planets that have been detected; the formation and evolution of these are not well understood. The primary paradigm is Jupiter, which [...]
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- 2004
6. Titan Surface Temperatures as Measured by Cassini CIRS
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Jennings, Donald E, Flasar, F.M, Kunde, V.G, Nixon, C.A, Romani, P.N, Samuelson, R.E, Coustenis, A, and Courtin, R
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Astronomy - Abstract
Thermal radiation from the surface of Titan reaches space through a spectral window of low opacity at 19-microns wavelength. This radiance gives a measure of the brightness temperature of the surface. Composite Infrared Spectrometer' (CIRS) observations from Cassini during its first four years at Saturn have permitted latitude mapping of zonally averaged surface temperatures. The measurements are corrected for atmospheric opacity using the dependence of radiance on emission angle. With the more complete latitude coverage and much larger dataset of CIRS we have improved upon the original results from Voyager IRIS. CIRS measures the equatorial surface brightness temperature to be 93.7+/-0.6 K, the same as the temperature measured at the Huygens landing site. The surface brightness temperature decreases by 2 K toward the south pole and by 3 K toward the north pole. The drop in surface temperature between equator and north pole implies a 50% decrease in methane saturation vapor pressure and relative humidity; this may help explain the large northern lakes. The H2 mole fraction is derived as a by-product of our analysis and agrees with previous results. Evidence of seasonal variation in surface and atmospheric temperatures is emerging from CIRS measurements over the Cassini mission.
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- 2009
7. Titan Surface Temperatures from Cassini CIRS
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Jennings, Donald E, Flasar, F.M, Kundle, V.G, Samuelson, R.E, Pearl, J.C, Nixon, C.A, Carlson, R.C, Mamoutkine, A.A, Brasunas, J.C, Guandique, E, Achterberg, R.K, Bjoraker, M.H, Romani, P.N, Segura, M.E, Albright, S.A, Elliott, M.H, Tingley, J.S, Calcutt, S, Coustenis, A, Bezard, B, and Courtin, R
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Lunar And Planetary Science And Exploration - Abstract
Thermal radiation from the surface of Titan reaches space through a spectral window at 19-microns wavelength. After removing the effects of the atmosphere, measurement of this radiance gives the brightness temperature of the surface. The Composite Infrared Spectrometer (CIRS) has made such measurements during the Cassini prime mission. These observations cover a wide range of emission angles, thereby constraining the contributions from atmospheric radiance and opacity. With the more complete latitude coverage and much larger dataset, we have been able to improve upon the original results from Voyager IRIS. CIRS measures an equatorial surface brightness temperature, averaged over longitude, of 93.7 +/- 0.6 K. This agrees with the HASI temperature at the Huygens landing site. The latitude dependence of surface brightness temperature exhibits an approximately 2 K decrease toward the South Pole and 3 K decrease toward the North Pole. The lower surface temperatures seen at high latitudes are consistent with conditions expected for lake formation.
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- 2008
8. Evolution of the stratospheric temperature and chemical composition over one titanian year
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Coustenis, A. Bampasidis, G. Achterberg, R.K. Lavvas, P. Jennings, D.E. Nixon, C.A. Teanby, N.A. Vinatier, S. Flasar, F.M. Carlson, R.C. Orton, G. Romani, P.N. Guandique, E.A. Stamogiorgos, S.
- Abstract
Since the Voyager 1 (V1) flyby in 1980, Titan's exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titanian year or 29.5 Earth years had elapsed in 2010 May). In this study, we search for temporal variations affecting Titan's atmospheric thermal and chemical structure within that year. We process Cassini/CIRS data taken during the Titan flybys from 2006-2013 and find a rather uneventful equatorial evolution. Conversely, at northern latitudes, we found enhanced abundances around the period of the northern spring equinox in mid-2009, which subsequently decreased (from 2010 to 2012), returning to values similar to those found in the V1 epoch, one Titanian year before. In the southern latitudes, since 2012, we see a trend for an increase of several trace gases (C4H2, C 3H4, and HCN), indicative of a seasonal atmospheric reversal setting in. When we compare the CIRS 2010 and the 1980 V1/IRIS spectra (reanalyzed here), we find limited inter-annual variations. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50°N to 50°S, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by general circulation and photochemical models. Exceptions concern the most complex hydrocarbons (C 4H2 and C3H4). We also consider data from ground-based and Earth-orbiting observatories (such as from the Infrared Space Observatory, revisited here) and discuss possible atmospheric composition trends during a Titanian year. © 2013. The American Astronomical Society. All rights reserved..
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- 2013
9. Thermal and chemical structure variations in Titan's stratosphere during the Cassini mission
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Bampasidis, G. Coustenis, A. Achterberg, R.K. Vinatier, S. Lavvas, P. Nixon, C.A. Jennings, D.E. Teanby, N.A. Flasar, F.M. Carlson, R.C. Moussas, X. Preka-Papadema, P. Romani, P.N. Guandique, E.A. Stamogiorgos, S.
- Abstract
We have developed a line-by-line Atmospheric Radiative Transfer for Titan code that includes the most recent laboratory spectroscopic data and haze descriptions relative to Titan's stratosphere. We use this code to model Cassini Composite Infrared Spectrometer data taken during the numerous Titan flybys from 2006 to 2012 at surface-intercepting geometry in the 600-1500 cm -1 range for latitudes from 50°S to 50°N. We report variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titan's stratosphere varies significantly with latitude during the 6 years investigated here, with increased mixing ratios toward the northern latitudes. In particular, we monitor and quantify the amplitude of a maximum enhancement of several gases observed at northern latitudes up to 50°N around mid-2009, at the time of the NSE. We find that this rise is followed by a rapid decrease in chemical inventory in 2010 probably due to a weakening north polar vortex with reduced lateral mixing across the vortex boundary. © 2012. The American Astronomical Society. All rights reserved..
- Published
- 2012
10. Titan trace gaseous composition from CIRS at the end of the Cassini-Huygens prime mission
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Coustenis, A. Jennings, D.E. Nixon, C.A. Achterberg, R.K. Lavvas, P. Vinatier, S. Teanby, N.A. Bjoraker, G.L. Carlson, R.C. Piani, L. Bampasidis, G. Flasar, F.M. Romani, P.N.
- Abstract
This paper reports on the results from an extensive study of all nadir-looking spectra acquired by Cassini/CIRS during the 44 flybys performed in the course of the nominal mission (2004-2008). With respect to the previous study (Coustenis, A., and 24 colleagues [2007]. Icarus 189, 35-62, on flybys TB-T10) we present here a significantly richer dataset with, in particular, more data at high northern and southern latitudes so that the abundances inferred here at these regions are more reliable. Our enhanced high-resolution dataset allows us to infer more precisely the chemical composition of Titan all over the disk. We also include improved spectroscopic data for some molecules and updated temperature profiles. The latitudinal distributions of all of the gaseous species are inferred. We furthermore test vertical distributions essentially for acetylene (C2H2) from CIRS limb-inferred data and from current General Circulation Models for Titan and compare our results on all the gaseous abundances with predictions from 1-D photochemical-radiative models to check the reliability of the chemical reactions and pathways. © 2009 Elsevier Inc.
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- 2010
11. Titan trace gaseous composition from CIRS at the end of the Cassini–Huygens prime mission
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Coustenis, A., primary, Jennings, D.E., additional, Nixon, C.A., additional, Achterberg, R.K., additional, Lavvas, P., additional, Vinatier, S., additional, Teanby, N.A., additional, Bjoraker, G.L., additional, Carlson, R.C., additional, Piani, L., additional, Bampasidis, G., additional, Flasar, F.M., additional, and Romani, P.N., additional
- Published
- 2010
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12. The 12C/13C isotopic ratio in Titan hydrocarbons from Cassini/CIRS infrared spectra
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Nixon, C.A., primary, Achterberg, R.K., additional, Vinatier, S., additional, Bézard, B., additional, Coustenis, A., additional, Irwin, P.G.J., additional, Teanby, N.A., additional, de Kok, R., additional, Romani, P.N., additional, Jennings, D.E., additional, Bjoraker, G.L., additional, and Flasar, F.M., additional
- Published
- 2008
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13. An intense stratospheric jet on Jupiter.
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Flasar, F.M., Kunde, V.G., Achterberg, R.K., Conrath, B.J., Simon-Miller, A.A., Nixon, C.A., Gierasch, P.J., Romani, P.N., Bézard, B., Irwin, P., Bjoraker, G.L., Brasunas, J.C., Jennings, D.E., Pearl, J.C., Smith, M.D., Orton, G.S., Spilker, L.J., Carlson, R., and Calcutt, S.B.
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STRATOSPHERE ,ATMOSPHERE of Jupiter ,ATMOSPHERE ,JUPITER (Planet) ,GLOBAL temperature changes ,EARTH (Planet) - Abstract
The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of ~140?m?s
-1 , whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere. [ABSTRACT FROM AUTHOR]- Published
- 2004
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14. Methane photochemistry and haze production on Neptune
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Romani, P.N., primary and Atreya, S.K., additional
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- 1988
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15. The 12C/13C isotopic ratio in Titan hydrocarbons from Cassini/CIRS infrared spectra
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Nixon, C.A., Achterberg, R.K., Vinatier, S., Bézard, B., Coustenis, A., Irwin, P.G.J., Teanby, N.A., de Kok, R., Romani, P.N., Jennings, D.E., Bjoraker, G.L., and Flasar, F.M.
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INFRARED spectra , *ATMOSPHERE , *METEOROLOGY , *EARTH (Planet) - Abstract
Abstract: We have analyzed infrared spectra of Titan recorded by the Cassini Composite Infrared Spectrometer (CIRS) to measure the isotopic ratio 12C/13C in each of three chemical species in Titan''s stratosphere: CH4, C2H2 and C2H6. This is the first measurement of 12C/13C in any C2 molecule on Titan, and the first measurement of 12CH4/13CH4 (non-deuterated) on Titan by remote sensing. Our spectra cover five widely-spaced latitudes, 65° S to 71° N and we have searched for both latitude variability of 12C/13C within a given species, and also for differences between the 12C/13C in the three gases. For CH4 alone, we find (1-σ), essentially in agreement with the 12CH4/13CH4 measured by the Huygens Gas Chromatograph/Mass Spectrometer instrument (GCMS) [Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779–784]: , and also with measured values in H13CN and 13CH3D by CIRS at lower precision [Bézard, B., Nixon, C., Kleiner, I., Jennings, D., 2007. Icarus 191, 397–400; Vinatier, S., Bézard, B., Nixon, C., 2007. Icarus 191, 712–721]. For the C2 species, we find in C2H2 and in C2H6, a possible trend of increasingly value with molecular mass, although these values are both compatible with the Huygens GCMS value to within error bars. There are no convincing trends in latitude. Combining all fifteen measurements, we obtain a value of , also compatible with GCMS. Therefore, the evidence is mounting that 12C/13C is some 8% lower on Titan than on the Earth (88.9, inorganic standard), and lower than typical for the outer planets ( [Sada, P.V., McCabe, G.H., Bjoraker, G.L., Jennings, D.E., Reuter, D.C., 1996. Astrophys. J. 472, 903–907]). There is no current model for this enrichment, and we discuss several mechanisms that may be at work. [Copyright &y& Elsevier]
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- 2008
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16. Meridional variations of C2H2 and C2H6 in Jupiter's atmosphere from Cassini CIRS infrared spectra
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Nixon, C.A., Achterberg, R.K., Conrath, B.J., Irwin, P.G.J., Teanby, N.A., Fouchet, T., Parrish, P.D., Romani, P.N., Abbas, M., LeClair, A., Strobel, D., Simon-Miller, A.A., Jennings, D.J., Flasar, F.M., and Kunde, V.G.
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ATMOSPHERE , *STRATOSPHERE , *ATMOSPHERIC temperature , *SPECTRUM analysis - Abstract
Abstract: Hydrocarbons such as acetylene (C2H2) and ethane (C2H6) are important tracers in Jupiter''s atmosphere, constraining our models of the chemical and dynamical processes. However, our knowledge of the vertical and meridional variations of their abundances has remained sparse. During the flyby of the Cassini spacecraft in December 2000, the Composite Infrared Spectrometer (CIRS) instrument was used to map the spatial variation of emissions from 10 to 1400 cm−1 (1000–7 μm). In this paper we analyze a zonally averaged set of CIRS spectra taken at the highest (0.48 cm−1) resolution, firstly to infer atmospheric temperatures in the stratosphere at 0.5–20 mbar via the band of CH4, and in the troposphere at 150–400 mbar, via the H2 absorption at 600–800 cm−1. Stratospheric temperatures at 5 mbar are generally warmer in the north than the south by 7–8 K, while tropospheric temperatures show no such asymmetry. Both latitudinal temperature profiles however do show a pattern of maxima and minima which are largely anti-correlated between the two levels. We then use the derived temperature profiles to infer the vertical abundances of C2H2 and C2H6 by modeling tropospheric absorption (∼200 mbar) and stratospheric emission (∼5 mbar) in the C2H2 and C2H6 bands, and also emission of the acetylene hotband (∼0.1 mbar). Acetylene shows a distinct north–south asymmetry in the stratosphere, with 5 mbar abundances greatest close to 20° N and decreasing from there towards both poles by a factor of ∼4. At 200 mbar in contrast, acetylene is nearly flat at a level of . Additionally, the abundance gradient of C2H2 between 10 and 0.1 mbar is derived, based on interpolated temperatures at 0.1 mbar, and is found to be positive and uniform with latitude to within errors. Ethane at both 5 and 200 mbar shows increasing VMR towards polar regions of ∼1.75 towards 70° N and ∼2.0 towards 70° S. An explanation for the meridional trends is proposed in terms of a combination of photochemistry and dynamics. Poleward, the decreasing UV flux is predicted to decrease the abundances of C2H2 and C2H6 by factors of 2.7 and 3.5, respectively, at latitude 70°. However, the lifetime of C2H6 in the stratosphere ( at 5 mbar) is much longer than the dynamical timescale for meridional mixing inferred from Comet SL-9 debris (), and therefore the rising abundance towards high latitudes likely indicates that meridional mixing dominates over photochemical effects. For C2H2, the opposite occurs, with the relatively short photochemical lifetime (), compared to meridional mixing times, ensuring that the expected photochemical trends are visible. [Copyright &y& Elsevier]
- Published
- 2007
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17. On the HCN and CO2 abundance and distribution in Jupiter's stratosphere
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Lellouch, E., Bézard, B., Strobel, D.F., Bjoraker, G.L., Flasar, F.M., and Romani, P.N.
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ATMOSPHERE , *STRATOSPHERE , *CHEMOSPHERE , *LATITUDE - Abstract
Abstract: Observations of Jupiter by Cassini/CIRS, acquired during the December 2000 flyby, provide the latitudinal distribution of HCN and CO2 in Jupiter''s stratosphere with unprecedented spatial resolution and coverage. Following up on a preliminary study by Kunde et al. [Kunde, V.G., and 41 colleagues, 2004. Science 305, 1582–1587], the analysis of these observations leads to two unexpected results (i) the total HCN mass in Jupiter''s stratosphere in 2000 was , i.e., at least three times larger than measured immediately after the Shoemaker–Levy 9 (SL9) impacts in July 1994 and (ii) the latitudinal distributions of HCN and CO2 are strikingly different: while HCN exhibits a maximum at 45° S and a sharp decrease towards high Southern latitudes, the CO2 column densities peak over the South Pole. The total CO2 mass is . A possible cause for the HCN mass increase is its production from the photolysis of NH3, although a problem remains because, while millimeter-wave observations clearly indicate that HCN is currently restricted to submillibar () levels, immediate post-impact infrared observations have suggested that most of the ammonia was present in the lower stratosphere near 20 mbar. HCN appears to be a good atmospheric tracer, with negligible chemical losses. Based on 1-dimensional (latitude) transport models, the HCN distribution is best interpreted as resulting from the combination of a sharp decrease (over an order of magnitude in ) of wave-induced eddy mixing poleward of 40° and an equatorward transport with velocity. The CO2 distribution was investigated by coupling the transport model with an elementary chemical model, in which CO2 is produced from the conversion of water originating either from SL9 or from auroral input. The auroral source does not appear adequate to reproduce the CO2 peak over the South Pole, as required fluxes are unrealistically high and the shape of the CO2 bulge is not properly matched. In contrast, the CO2 distribution can be fit by invoking poleward transport with a velocity and vigorous eddy mixing (). While the vertical distribution of CO2 is not measured, the combined HCN and CO2 results imply that the two species reside at different stratospheric levels. Comparing with the circulation regimes predicted by earlier radiative-dynamical models of Jupiter''s stratosphere, and with inferences from the ethane and acetylene stratospheric latitudinal distribution, we suggest that CO2 lies in the middle stratosphere near or below the 5-mbar level. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
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