New wind measurements in Venus’ lower mesosphere from visible spectroscopy |
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| Institution: | 1. LESIA, Observatoire de Paris, UMR CNRS 8109, F-92195 Meudon cedex, France;2. Laboratoire de Spectrométrie Physique, UMR CNRS 5588, Université Joseph Fourier, F-38041 Grenoble cedex 9, France;1. Dpto. Física Aplicada I, Escuela de Ingeniería de Bilbao, UPV/EHU, 48013, Bilbao, Spain;2. Sistemen Ingeniaritza eta Automatika Saila, Bilboko Ingeniaritza Eskola UPV/EHU, 48013, Bilbao, Spain;3. LESIA, Observatoire de Paris, CNRS, PSL Research University, UMPC, Université Denis Diderot, 5 Place Jules Janssen, Meudon, France;4. DIO, Observartoire de Paris, CNRS, PSL Research University, 61 Av. de l''Observatoire, Paris, France;1. Planetary Aeronomy, Belgian Institute for Space Aeronomy, 3 av. Circulaire, 1180 Brussels, Belgium;2. Fonds National de la Recherche Scientifique, 5 rue d?Egmont, 1000 Brussels, Belgium;3. LATMOS, 11 Bd d?Alembert, 78280 Guyancourt, France;1. LESIA-Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France;2. CAAUL-Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Ed. Leste, Tapada da Ajuda, 1349-018 Lisboa, Portugal;3. Université de Versailles-Saint-Quentin – EA2449 – 47, Boulevard Vauban, 78047 Guyancourt Cedex, France;4. Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal;5. Instituto de Astrofísica de Andalucía, (CSIC), Glorieta de la Astronomía, 18008 Granada, Spain;1. Université Versailles St-Quentin; Sorbonne Universités, UPMC Univ. Paris 06; CNRS/INSU, LATMOS-IPSL, 11 bd d’Alembert 78280 Guyancourt, France;2. Sorbonne Universités, UPMC Univ. Paris 06; CNRS/INSU, LMD-IPSL, 4 Place Jussieu, 75252 Paris Cedex 05, France;3. Sorbonne Universités, UPMC Univ. Paris 06; Université Versailles St-Quentin; CNRS/INSU, LATMOS-IPSL, 4 Place Jussieu, 75252 Paris Cedex 05, France |
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| Abstract: | The dynamics of Venus’ mesosphere (70–110 km) is characterized by the superposition of two different wind regimes: (1) Venus’ retrograde superrotation; (2) a sub-solar to anti-solar (SS–AS) flow pattern, driven by solar EUV heating on the sunlit hemisphere. Here, we report on new ground-based velocity measurements in the lower part of the mesosphere. We took advantage of two essentially symmetric Venus elongations in 2001 and 2002 to perform high-resolution Doppler spectroscopy (R=120,000) in 12C16O2 visible lines of the 5ν3 band and in a few solar Fraunhofer lines near 8700 Å. These measurements, mapped over several points on Venus’ illuminated hemisphere, probe the region of cloud tops. More precisely, the solar Fraunhofer lines sample levels a few kilometers below the UV features (i.e. near ～67 km), while the CO2 lines probe an altitude higher by about 7 km. The wind field over Venus’ disk is retrieved with an rms uncertainty of 15–25 m s?1 on individual measurements. Kinematical fit to a one- or two-component circulation model indicates the dominance of the zonal retrograde flow with a mean equatorial velocity of ～75 m s?1, exhibiting very strong day-to-day variations (±65 m s?1). Results are very consistent for the two kinds of lines, suggesting a negligible vertical wind shear over 67–74 km. The SS–AS flow is not detected in single-day observations, but combining the results from all data suggests that this component may invade the lower mesosphere with a ～40 m s?1 velocity. |
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