The distribution of carbon monoxide in the lower atmosphere of Venus |
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| Authors: | Daniel V Cotton Jeremy Bailey D Crisp VS Meadows |
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| Institution: | 1. School of Physics, University of New South Wales, NSW 2052, Australia;2. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, United States;3. Department of Astronomy, University of Washington, Box 351580, Seatlle, WA 98195, United States;4. NASA Astrobiology Institute, Virtual Planetary Laboratory Lead Team;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: | We have obtained spatially resolved near-infrared spectroscopy of the Venus nightside on 15 nights over three observing seasons. We use the depth of the CO absorption band at 2.3 μm to map the two-dimensional distribution of CO across both hemispheres. Radiative transfer models are used to relate the measured CO band depth to the volume mixing ratio of CO. The results confirm previous investigations in showing a general trend of increased CO abundances at around 60° latitude north and south as compared with the equatorial regions. Observations taken over a few nights generally show very similar CO distributions, but significant changes are apparent over longer periods. In past studies it has been assumed that the CO latitudinal variation occurs near 35 km altitude, at which K-band sensitivity to CO is greatest. By modeling the detailed spectrum of the excess CO at high latitudes we show that it occurs at altitudes around 45 km, much higher than has previously been assumed, and that there cannot be significant contribution from levels of 36 km or lower. We suggest that this is most likely due to downwelling of CO-rich gas from the upper atmosphere at these latitudes, with the CO being removed by around 40 km through chemical processes such as the reaction with SO3. |
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