Vertical profiling of SO2 and SO above Venus’ clouds by SPICAV/SOIR solar occultations |
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| Authors: | Denis A Belyaev Franck Montmessin Jean-Loup Bertaux Arnaud Mahieux Anna A Fedorova Oleg I Korablev Emmanuel Marcq Yuk L Yung Xi Zhang |
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| Institution: | 1. LATMOS, CNRS/INSU/IPSL, Quartier des Garennes, 11 bd. d’Alembert, 78280 Guyancourt, France;2. Space Research Institute (IKI), 84/32 Profsoyuznaya Str., 117997 Moscow, Russia;3. Belgian Institute for Space Aeronomy, 3 Av. Circulaire, B-1180 Brussels, Belgium;4. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA;1. Cornell University, Dept of Astronomy, 318 Space Sciences Building, Ithaca, NY, 14853, USA;2. Observatoire de Paris, LESIA, 5 Place Jules Janssen, 92195 Meudon Cedex, France;3. University of Wisconsin-Madison, Space Science and Engineering Center, 1225 West Dayton Street, Madison, WI 53706, USA;4. Jet Propulsion Laboratory, M/S 183-501, 4800 Oak Grove Drive, Pasadena, CA 91109 USA |
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| Abstract: | New measurements of sulfur dioxide (SO2) and monoxide (SO) in the atmosphere of Venus by SPICAV/SOIR instrument onboard Venus Express orbiter provide ample statistics to study the behavior of these gases above Venus’ clouds. The instrument (a set of three spectrometers) is capable to sound atmospheric structure above the clouds in several observation modes (nadir, solar and stellar occultations) either in the UV or in the near IR spectral ranges. We present the results from solar occultations in the absorption ranges of SO2 (190–230 nm, and at 4 μm) and SO (190–230 nm). The dioxide was detected by the SOIR spectrometer at the altitudes of 65–80 km in the IR and by the SPICAV spectrometer at 85–105 km in the UV. The monoxide’s absorption was measured only by SPICAV at 85–105 km. We analyzed 39 sessions of solar occultation, where boresights of both spectrometers are oriented identically, to provide complete vertical profiling of SO2 of the Venus’ mesosphere (65–105 km). Here we report the first firm detection and measurements of two SO2 layers. In the lower layer SO2 mixing ratio is within 0.02–0.5 ppmv. The upper layer, also conceivable from microwave measurements by Sandor et al. (Sandor, B.J., Todd Clancy, R., Moriarty-Schieven, G., Mills, F.P. 2010]. Icarus 208, 49–60) is characterized by SO2 increasing with the altitude from 0.05 to 2 ppmv, and the SO2]/SO] ratio varying from 1 to 5. The presence of the high-altitude SOx species could be explained by H2SO4 photodissociation under somewhat warmer temperature conditions in Venus mesosphere. At 90–100 km the content of the sulfur dioxide correlates with temperature increasing from 0.1 ppmv at 165–170 K to 0.5–1 ppmv at 190–192 K. It supports the hypothesis of SO2 production by the evaporation of H2SO4 from droplets and its subsequent photolysis at around 100 km. |
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