Thermal spectroscopy of Neptune: The stratospheric temperature, hydrocarbon abundances, and isotopic ratios

Orton, Glenn S.; Lacy, J. H.; Achtermann, J. M.; Parmar, P. S.; Blass, W. E.

doi:10.1016/0019-1035(92)90117-p

Cited by 55 publications

(34 citation statements)

References 55 publications

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“…10). Nevertheless, it is consistent with other infrared spectroscopic measurements of the C 2 H 6 emission from heterodyne techniques (1.9 × 10 −6 with a factor of four uncertainty, Kostiuk et al 1992), echelle spectroscopy (1.0 +0.2 −0.8 × 10 −6 , Orton et al 1992) and Voyager/IRIS (1.5 +2.5 −0.5 × 10 −6 , Bézard et al 1991). Furthermore, the close correspondence between the photochemical model and the AKARI result in Fig.…”

Section: Atmospheric Compositionsupporting

confidence: 90%

“…This result is consistent with the modelling of visible CH 4 absorption spectra by Baines & Hammel (1994), who found stratospheric abundance in the range 0.2−17.0 × 10 −4 , with an optimum value of 3.5×10 −4 . Furthermore, the ranges of CH 4 mole fractions quoted by Orton et al (1992) (1.9−26.1 × 10 −4 ) and Orton et al (2007) (7.5−15.0 × 10 −4 ) encompass the AKARI results at mbar pressures. Most importantly, the optimum value for CH 4 is consistent within the errors with the stratospheric abundance of 7.5 × 10 −4 used in the photochemical modeling of Moses et al (2005), discussed below.…”

Section: Atmospheric Compositionsupporting

confidence: 55%

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Neptune's atmospheric composition from AKARI infrared spectroscopy

Fletcher

Drossart

Burgdorf

et al. 2010

A&A

115

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Aims. Disk-averaged infrared spectra of Neptune between 1.8 and 13 μm, obtained by the AKARI infrared camera (IRC) in May 2007, have been analysed to (a) determine the globally-averaged stratospheric temperature structure; (b) derive the abundances of stratospheric hydrocarbons; and (c) detect fluorescent emission from CO at 4.7 μm. Methods. Mid-infrared spectra (SG1 and SG2 channels of AKARI/IRC), with spectral resolutions of 47 and 34 respectively, were modelled using a line-by-line radiative transfer code to determine the temperature structure between 1-1000 μbar and the abundances of CH 4 , CH 3 D and higher-order hydrocarbons. A full non-LTE radiative model was then used to determine the best fitting CO profile to reproduce the fluorescent emission observed at 4.7 μm in the NG channel (with a spectral resolution of 135). Results. The globally-averaged stratospheric temperature structure is quasi-isothermal between 1-1000 μbar, which suggests little variation in global stratospheric conditions since studies by the Infrared Space Observatory a decade earlier. The derived CH 4 mole fraction of (9.0 ± 3.0) × 10 −4 at 50 mbar, decreasing to (0.9 ± 0.3) × 10 −4 at 1 μbar, is larger than that expected if the tropopause at 56 K acts as an efficient cold trap, but consistent with the hypothesis that CH 4 leaking through the warm south polar tropopause (62-66 K) is globally redistributed by stratospheric motion. The ratio of D/H in CH 4 of 3.0 ± 1.0 × 10 −4 supports the conclusion that Neptune is enriched in deuterium relative to the other giant planets. We determine a mole fraction of ethane of (8.5 ± 2.1) × 10 −7 at 0.3 mbar, consistent with previous studies, and a mole fraction of ethylene of 5.0 +1.8 −2.1 × 10 −7 at 2.8 μbar. An emission peak at 4.7 μm is interpreted as a fluorescent emission of CO, and requires a vertical distribution with both external and internal sources of CO. Finally, comparisons to previous L-band studies indicate significant variability of Neptune's flux densities in the 3.5-4.1 μm range, related to changes in solar energy deposition.

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Section: Atmospheric Compositionsupporting

confidence: 90%

Section: Atmospheric Compositionsupporting

confidence: 55%

Neptune's atmospheric composition from AKARI infrared spectroscopy

Fletcher

Drossart

Burgdorf

et al. 2010

A&A

115

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“…Mid-infrared wavelengths are dominated by the collision-induced opacity of H 2 and He, along with the collection of hydrocarbons resulting from a chain of photochemical reactions initiated by UV photolysis of methane (e.g., Orton et al, 1987;Moses et al, 2005). Ethane at 12 µm was first observed by Gillett and Rieke (1977), and together with methane at 7.7 µm dominates the N-band (7-13 µm) spectrum of Neptune (Orton et al, 1992). Photometric imaging or spectroscopy is sensitive to emission from the stratosphere (0.1 mbar) down to the upper troposphere (200 mbar), and the measurement of a broad thermal-IR wavelength range allows us to disentangle the various contributions (temperatures, composition, aerosols) to the upwelling radiance.…”

Section: Introductionmentioning

confidence: 99%

Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007

Fletcher

Pater²,

Orton

et al. 2014

Icarus

Self Cite

108

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• ). 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 < ±5 K at 1 mbar and < ±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 (from 500 to 1200 ppb at 1 mbar). The retrieved C 2 H 6 abundances are extremely sensitive to the details of the T (p) derivation, although the underlying cause of the variable ethane emission remains unidentified. Stratospheric temperatures and ethane are found to be latitudinally uniform away from the south pole (assuming a latitudinally-uniform distribution of stratospheric methane), with no large seasonal hemispheric asymmetries evident at solstice. At low and mid-latitudes, 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 µm mapping of tropospheric temperatures and para-hydrogen disequilibrium (a tracer for vertical motions) suggests a symmetric meridional circulation with cold air rising at mid-latitudes (sub-equilibrium para-H 2 conditions) and warm air sinking at the equator and poles (super-equilibrium para-H 2 conditions). The most significant atmospheric changes have occurred at high southern latitudes, where zonal temperatures retrieved from 2003 images suggest a polar enhancement of 7-8 K above the tropopause, and an increase of 5-6 K throughout the 70 − 90• S region between 0.1 and 200 mbar. Such a large perturbation, if present in 1989, would have been detectable by Voyager/IRIS in a single scan despite its long-wavelength sensitivity, and we conclude that Neptune's south polar cyclonic vortex increased in strength significantly from Voyager to solstice.

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“…9 and 10. These coefficients have been calculated using the semi-classical model of Robert and Bonamy [22] under the assumption that CH 3 …”

Section: Comparison Of Measured Air-broadening Coefficients With Theomentioning

confidence: 99%

“…Laboratory spectroscopic studies of the vibrational bands of CH 3 of CH 3 D have been published [11][12][13]. Devi et al [14] measured N 2 -and air-broadening coefficients for 24 lines and self-broadening coefficients for 2 lines in the ν 6 band at room temperature.…”

Section: Introductionmentioning

confidence: 99%

Experimental air-broadened line parameters in the\bm{ u}\textsubscript band of CH\textsubscriptD

Predoi‐Cross

Brawley-Tremblay²,

Povey³

et al. 2007

Can. J. Phys.

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In this study we report the first experimental measurements of air-broadening and air-induced This paper is a continuation of our study of spectroscopic line parameters in the ν 2 band of CH 3 D [8][9][10] EXPERIMENTAL DETAILSThe seventeen pure gas and air-broadened absorption spectra used in this work were recorded at an unapodized resolution of 0.0056 cm -1 using the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory (NSO) on Kitt Peak, Arizona. The experimental conditions for the self-broadened spectra have been reported in Ref.8. In Table 1 we present only the experimental conditions for the air-broadened spectra used in this study.Three absorption cells with path lengths of 10.2, 25 and 150 cm were used in the experiments.The spectra covering the 2048-2318 cm -1 were simultaneously fit using a multispectrum nonlinear least-squares procedure [23]. Using this analysis tool we were able to combine spectra 5 recorded with low pressures of 98% pure CH 3 D, self-broadened spectra and lean mixtures (~1%)of CH 3 D in air in a single non-linear least-squares solution. This methodology avoids having to give highly accurate input values for line intensities, self-broadening and self-induced pressure shifts. Instead, these parameters are determined from the pure gas spectra during the multispectrum fit. The experimental setup and data reduction methods were described in detail in our study to self-broadening and self-induced pressure shifts of CH RESULTS AND DISCUSSIONThe CH 3 D absorption spectra were analyzed using a multispectrum analysis software The air-broadening coefficients and air-pressure induced shift coefficients for CH 3 D transitions in the ν 2 band retrieved from our multispectrum analysis are presented in Table 2. The errors quoted in parentheses represent two standard deviation uncertainties in the measured quantities in units of the last quoted digit. These errors represent twice the uncertainties as obtained from the multispectrum least-squares fits. By reporting twice the standard deviation uncertainties we hope to take into account any systematic errors arising from other sources such as calibration standards, pressure and temperature determinations and mixing ratio uncertainties are difficult to asses.The air-broadening coefficients are given in units of cm −1 atm −1 at 296 K. For each transition we list the line center positions retrieved from the fits (in cm −1 ) and the transitions quantum numbers. In our analysis we have not applied any temperature corrections to the measured pressure-shift coefficients. Hence, the pressure-shift coefficients listed in Table 2 7 correspond to values at the mean temperature (298 ± 2 K) at which the spectra were recorded. A small temperature correction was applied to the air-broadening coefficients using the temperature dependence coefficients reported in the HITRAN database. We present our results arranged in groups of Q P-, Q Q-, and Q R-branches. Within each branch, the results are arranged separately for the A-an...

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Thermal spectroscopy of Neptune: The stratospheric temperature, hydrocarbon abundances, and isotopic ratios

Cited by 55 publications

References 55 publications

Neptune's atmospheric composition from AKARI infrared spectroscopy

Neptune's atmospheric composition from AKARI infrared spectroscopy

Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007

Experimental air-broadened line parameters in the\bm{ u}\textsubscript band of CH\textsubscriptD

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