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In this paper we present the first night side distribution of SO 2 content in Venus’ upper mesosphere (altitudes from 85 to 105 km). The dataset is based on the SPICAV UV stellar occultation experiment which took place onboard ESA's Venus Express (VEX) orbiter in 2006–2014. The UV channel of SPICAV spectrometer detected absorption bands of SO 2 and CO 2 in the spectral range 180–300 nm with a resolution of 1–2 nm while stellar light was occulted by the mesosphere. Altitude profiles of sulfur dioxide's volume mixing ratio (VMR) could be retrieved in the upper part of the mesosphere covering the whole night side on Venus. In parallel, we have reprocessed the terminator UV solar occultations dataset ( Belyaev et al., 2012 . Icarus 217 , 740–751) in the same altitude range and extended its statistics until 2014. On average the SO 2 VMR increases with altitude from 10–30 ppb at 85 km to 100–300 ppb at 100 km in both regimes of occultation. The midnight SO 2 abundance appears to be 3–4 times higher than in the terminator region: 150–200 ppbv versus 50 pppv at altitude around 95 km. These new results were compared with the distribution of oxygen atoms, which are tracers of the global subsolar-antisolar (SS-AS) circulation at ∼100 km (the data provided by Soret et al., 2012 Icarus, 217, 849–855). The night time behavior looks similar for SO 2 molecules and O atoms with a correlation coefficient R corr = 0.73. Moreover, the retrieved SO 2 enrichment above 85 km appears to correlate with the density of H 2 SO 4 droplets ( Luginin et al., 2016 ; Icarus 277, 154–170). [ABSTRACT FROM AUTHOR]

Intensities of the spectral lines in the fundamental bands of D35Cl and DF were calculated using the semi-empirical dipole moment functions derived from the most accurate and precise measurements of intensities of the ro-vibrational lines of H35Cl and HF. Values obtained in this way for the deuterated species are superior to any available measured or calculated data to date. Our study of the D/H ratios in H2O, HCl, and HF on Venus is based on spatially-resolved high-resolution spectroscopy using the CSHELL spectrograph at NASA IRTF. Search for DF on Venus using its R5 (1-0) line at 3024.054cm−1 results in a DF mixing ratio of 0.23±0.11ppb that corresponds to (D/H)HF =420±200 times that in the Standard Mean Ocean Water (SMOW). H2O abundances on Venus were retrieved using lines at 3022.366 and 3025.761cm−1 that were observed at an exceptionally low overhead telluric water abundance of 0.3pr.mm. The measured H2O mixing ratios at 74km vary insignificantly between 55°S and 55°N with a mean value of 3.2ppm. When compared with simultaneous observations of HDO near 2722cm−1, this results in (D/H)H2O =95±15 times SMOW. Reanalysis of the observation of the D35Cl R4 (1-0) line at 2141.540cm−1 (Krasnopolsky, V.A. [2012b]. Icarus 219, 244–249) using the improved line strength and more thorough averaging of the spectra gives (D/H)HCl =190±50 times SMOW. The similarity of the measured (D/H)H2O =95±15 at 74km with 120±40 observed by De Bergh et al. (De Bergh, C., Bezard, B., Owen, T., Crisp, D., Maillard, J.P., Lutz, B.L. [1991]. Science 251, 547–549) below the clouds favors the constant (D/H)H2O from the surface to the mesosphere, in accord with the prediction by theory. D/H≈100 removes a difference of a factor of 2 between H2O abundances in the observations by Krasnopolsky (Krasnopolsky, V.A. [2010b]. Icarus 209, 314–322) and the Venus Express nadir observations (Cottini, V., Ignatiev, N.I., Piccioni, G., Drossart, P., Grassi, D., Markiewicz, W.J. [2012]. Icarus 217, 561–569). Equivalent widths of the HDO and H2O lines are similar in our observations; therefore some errors cancel out in their ratios. Photochemistry of HCl in the mesosphere tends to enrich D in HCl and deplete it in H2O. This may be an explanation of the twofold difference between the observed D/H in HCl and H2O. An alternative explanation is based on (D/H)H2O ≈200 observed in the mesosphere by Bjoraker et al. (Bjoraker, G.L., Larson, H.P., Mumma, M.J., Timmermann, R., Montani, J.L. [1992]. Bull. Am. Astron. Soc. 24, 995) and Fedorova et al. (Fedorova, A. et al. J. Geophys. Res. 113, E00B22). This means an effective exchange of D between H2O and HCl and almost equal D/H in both species. However, this requires a twofold increase in D/H from the lower atmosphere to the mesosphere. This increase is not supported by theory; furthermore, condensation processes usually deplete D/H above the clouds. Photochemistry of HF has not been studied; it proceeds mostly in the lower thermosphere, and D/H in HF may be very different from that in H2O. Overall, the observational data on D/H in all hydrogen-bearing species on Venus are helpful to solve the problem of deuterium fractionation on Venus. [ABSTRACT FROM AUTHOR]

Abstract: The infrared AOTF spectrometer is a part of the SPICAM experiment onboard the Mars-Express ESA mission. The instrument has a capability of solar occultations and operates in the spectral range of 1–1.7 μm with a spectral resolution of ∼3.5 cm−1. We report results from 24 orbits obtained during MY28 at 130°–160°, and the latitude range of 40°–55° N. For these orbits the atmospheric density from 1.43 μm CO2 band, water vapor mixing ratio based on 1.38 μm absorption, and aerosol opacities were retrieved simultaneously. The vertical resolution of measurements is better than 3.5 km. Aerosol vertical extinction profiles were obtained at 10 wavelengths in the altitude range from 10 to 60 km. The interpretation using Mie scattering theory with adopted refraction indices of dust and H2O ice allows to retrieve particle size () and number density (∼1 cm−3 at 15–30 km) profiles. The haze top is generally below 40 km, except the longitude range of 320°–50° E, where high-altitude clouds at 50–60 km were detected. Optical properties of these clouds are compatible with ice particles (effective radius , number density ) distributed with variance . The vertical optical depth of the clouds is below 0.001 at 1 μm. The atmospheric density profiles are retrieved from CO2 band in the altitude range of 10–90 km, and H2O mixing ratio is determined at 15–50 km. Unless a supersaturation of the water vapor occurs in the martian atmosphere, the H2O mixing ratio indicates ∼5 K warmer atmosphere at 25–45 km than predicted by models. [Copyright &y& Elsevier]