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One of the difficulties in modeling Venus’ nightside atmospheric windows is the need to apply CO 2 continuum opacity due to collision-induced CO 2 bands and/or extreme far wings of strong allowed CO 2 bands. Characterizing the CO 2 continuum absorption at near-IR wavelengths as well as searching for a possible vertical gradient of minor species near the surface require observations over different surface elevations. The largest change in altitude occurs during a passage above Maxwell Montes at high northern latitudes. In 2011, 2012 and 2013 the SPICAV instrument aboard the Venus Express satellite performed three sets of observations over Maxwell Montes with variation of surface altitude from −2 to 9 km in the 1.10, 1.18 and 1.28-μm windows. The retrieved CO 2 continuum absorption for the 1.10- and 1.18-μm windows varies from 0.29 to 0.66×10 −9 cm −1 amagat −2 and from 0.30 to 0.78×10 −9 cm −1 amagat −2 , respectively, depending on the assumed input parameters. The retrieval is sensitive to possible variations of the surface emissivity. Our values fall between the results of Bézard et al., (2009, 2011) based on VIRTIS-M observations and laboratory measurements by Snels et al. (2014) . We can also conclude that the continuum absorption at 1.28 μm can be constrained below 2.0×10 −9 cm −1 amagat −2 . Based on the 1.18 μm window the constant H 2 O mixing ratio varying from 25.7 +1.4 –1.2 ppm to 29.4 +1.6 –1.4 ppm has been retrieved assuming the surface emissivity of 0.95 and 0.6, respectively. No firm conclusion from SPICAV data about the vertical gradient of water vapor content at 10–20 km altitude could be drawn because of low signal-to-noise ratio and uncertainties in the surface emissivity. [ABSTRACT FROM AUTHOR]

In July 1994, the Shoemaker–Levy 9 (SL9) impacts introduced hydrogen cyanide (HCN) to Jupiter at a well confined latitude band around -44°, over a range of specific longitudes corresponding to each of the 21 fragments (Bézard et al. 1997, Icarus 125, 94–120). This newcomer to Jupiter''s stratosphere traces jovian dynamics. HCN rapidly mixed with longitude, so that observations recorded later than several months after impact witnessed primarily the meridional transport of HCN north and south of the impact latitude band. We report spatially resolved spectroscopy of HCN emission 10 months and 6 years following the impacts. We detect a total mass of HCN in Jupiter''s stratosphere of 1.5±0.7×1013 g in 1995 and 1.7±0.4×1013 g in 2000, comparable to that observed several days following the impacts (Bézard et al. 1997, Icarus 125, 94–120). In 1995, 10 months after impact, HCN spread to -30° and -65° latitude (half column masses), consistent with a horizontal eddy diffusion coefficient of Kyy=2–3×1010 cm2 s-1. Six years following impact HCN is observed in the northern hemisphere, while still being concentrated at 44° south latitude. Our meridional distribution of HCN suggests that mixing occurred rapidly north of the equator, with Kyy=2–5×1011 cm2 s-1, consistent with the findings of Moreno et al. (2003, Planet. Space Sci. 51, 591–611) and Lellouch et al. (2002, Icarus 159, 112–131). These inferred eddy diffusion coefficients for Jupiter''s stratosphere at 0.1–0.5 mbar generally exceed those that characterize transport on Earth. The low abundance of HCN detected at high latitudes suggests that, like on Earth, polar regions are dynamically isolated from lower latitudes. [Copyright &y& Elsevier]

Abstract: In this paper we apply a recently released set of methane line parameters () to the modeling of Titan spectra in the 1.58μm window at both low and high spectral resolution. We first compare the methane absorption based on this new set of methane data to that calculated from the methane absorption coefficients derived in situ from DISR/Huygens () and from the band models of and . The band model clearly underestimates the absorption in the window at temperature–pressure conditions representative of Titan’s troposphere, while the band model gives an acceptable agreement in the whole window, overestimating the absorption by about 15% in the range 6300–6500cm−1. We also find that the transmittance of Titan’s atmosphere is in excellent agreement with that calculated from the coefficients after reducing them by about 7%. Synthetic spectra computed with spectral resolutions of 1.2cm−1 (R∼5400) and 0.35cm−1 (R∼18000) are then compared with two high-resolution Earth-based measurements of Titan’s albedo obtained in 1982 and 1993 (with KPNO/FTS and IRTF/CSHELL). The new set of methane line parameters leads to an excellent match of all the CH3D and CH4 absorption features in these spectra, and permits us to derive a ratio of CH3D/CH4=(4.5±1.0)×10−4 – hence a D/H ratio in methane for Titan of (1.13±0.25)×10−4 – and a CO mole fraction of 40±10ppm (from the KPNO/FTS dataset) and 51±7ppm (from the IRTF/CSHELL dataset). We also infer constraints on the far-wing lineshape of methane lines of the 2ν 3 band. We finally present two other examples of models of Titan’s spectrum using the new line parameters, one potentially useful for future higher-resolution (R=40,000) observations, another one applicable to the ongoing low-resolution (R∼100) observations by Cassini VIMS. We show that the aerosol model of produces too much intensity at low phase angle compared to a VIMS spectrum recorded near the Huygens site and we propose a slightly revised model that reproduces this observation. [Copyright &y& Elsevier]

Abstract: Measurements of the vertical and latitudinal variations of temperature and C2H2 and C2H6 abundances in the stratosphere of Saturn can be used as stringent constraints on seasonal climate models, photochemical models, and dynamics. The summertime photochemical loss timescale for C2H6 in Saturn''s middle and lower stratosphere ( years, depending on altitude and latitude) is much greater than the atmospheric transport timescale; ethane observations may therefore be used to trace stratospheric dynamics. The shorter chemical lifetime for C2H2 ( years depending on altitude and latitude) makes the acetylene abundance less sensitive to transport effects and more sensitive to insolation and seasonal effects. To obtain information on the temperature and hydrocarbon abundance distributions in Saturn''s stratosphere, high-resolution spectral observations were obtained on September 13–14, 2002 UT at NASA''s IRTF using the mid-infrared TEXES grating spectrograph. At the time of the observations, Saturn was at a , corresponding to Saturn''s southern summer solstice. The observed spectra exhibit a strong increase in the strength of methane emission at 1230 cm−1 with increasing southern latitude. Line-by-line radiative transfer calculations indicate that a temperature increase in the stratosphere of from the equator to the south pole between 10 and 0.01 mbar is implied. Similar observations of acetylene and ethane were also recorded. We find the 1.16 mbar mixing ratio of C2H2 at and planetocentric latitude to be and , respectively. The C2H2 mixing ratio at 0.12 mbar is found to be at planetocentric latitude and at planetocentric latitude. The 2.3 mbar mixing ratio of C2H6 inferred from the data is and at and planetocentric latitude, respectively. Further observations, creating a time baseline, will be required to completely resolve the question of how much the latitudinal variations of C2H2 and C2H6 are affected by seasonal forcing and/or stratospheric circulation. [Copyright &y& Elsevier]

Ultraviolet spectral imaging has been a powerful tool to investigate the cloud top of Venus, allowing for measurement of several minor gases (especially SO 2 , SO, O 3), of cloud top aerosol's microphysical properties and of atmospheric dynamics through tracking of the unevenly distributed UV absorber. After a brief review of recent UV instruments that orbited around Venus, we present the results of a state-of-the-art radiative transfer model from Marcq et al. (2020) to derive the spectral resolution and Signal-to-Noise ratio (SNR) required to derive abundances of these gases, retrieve optical properties of the aerosols beyond our current knowledge. This leads us to propose a two-channel UV hyperspectral push-broom imager called VeSUV (standing for Venusian Spectroscopy in UV) whose technical characteristics will improve on existing measurements by a factor of at least 2, and which is well suited to the integration into the payload of future low Venus orbit platforms such as the proposed EnVision mission to ESA M5 call. [ABSTRACT FROM AUTHOR]

Abstract: Insufficient knowledge of the near infrared spectrum of methane is an important limitation for the analysis of the spectra of Titan and of the outer planetary atmospheres in general. The work reported here is the result of a long-term project aiming to provide astronomers with a line by line list for precise calculations of the methane absorption in the near infrared region. We thus present here our best to date empirical line list between 5854 and 7919cm−1 (1.71–1.26μm) and apply it to Titan, demonstrating its capability to significantly improve planetary spectral analysis. In recent contributions, we have obtained empirical line lists at room temperature and at 80K (suitable for Titan conditions) from spectra recorded by (i) Differential Absorption Spectroscopy (DAS) in the high energy part of the tetradecad (5854–6195cm−1) and in the icosad (6717–7589cm−1) (ii) high sensitivity CW-Cavity Ring Down Spectroscopy (CRDS) in the 1.58μm and 1.28μm transparency windows (6165–6750cm−1 and 7541–7919cm−1, respectively). In this work, we construct the global line lists for methane in “natural” isotopic abundance, covering the entire spectral region from 5854 to 7919cm−1. These WKMC (for Wang, Kassi, Mondelain, Campargue) empirical lists include 42,988 and 46,320 lines at 80±3K and 296±3K, respectively and are assembled here with some important improvements: [(i)] New spectroscopic parameters for the 5854–6148cm−1 region at 80K which increase significantly the number of observations and lower state energy determinations. [(ii)] Transitions of 13CH4 and CH3D were systematically identified by comparison with DAS spectra of highly enriched 13CH4 and CH3D, recorded at the same temperatures. [(iii)] In the 1.58μm transparency window where CH3D lines contribute importantly to the methane spectrum at 80K, the set of CH3D lower state energy values was completed by using recent DAS results for pure CH3D. The “two temperature method” provided lower state energy values for about 24,000 transitions from the ratios of their line intensities at 80K and 296K. The clear propensity of the derived low J values of 12CH4 and 13CH4 to be integer illustrates the quality of the lower state energy values. The obtained data sets allow us to account for most of the temperature dependence of the absorption over the considered region. To illustrate the interest of the WKMC line lists for planetary applications, we perform simulations of Titan spectra at different resolutions taken from the ground with instruments such as the FTS at the CFHT and CRIRES at the VLT or by the DISR instrument on board the Huygens probe. The agreement between the simulations and the observations clearly demonstrates an important improvement with respect to previous works. [Copyright &y& Elsevier]