Water and its isotopologues mesospheric distributions at the Venus terminator as measured by SOIR/VEx
Abstract
SOIR was an infrared echelle spectrometer on board the ESA Venus Express mission (2006-2014) (Nevejans et al., 2006). It performed solar occultations of the Venus mesosphere and thermosphere in the 2.2 to 4.4 µm range (Mahieux et al., 2008). It studied both sides of the terminator and the database covers all latitudes. Its very high spectral resolution (approx. 0.2 cm$ ^{-1}$) and spectral sampling (approx. 0.04 cm$ ^{-1}$) resolved the ro-vibrational lines of the atmospheric gases. Vertical profiles were retrieved from the spectra. SOIR was sensitive to the main species absorbing in the upper atmosphere (Vandaele et al., 2016): CO$ _{2}$ (Mahieux et al., 2012), CO (Vandaele et al., 2015), H$ _{2}$O (Chamberlain et al., 2020), HCl, HF (Mahieux et al., 2015c), SO$ _{2}$ (Mahieux et al., 2015b), and the aerosols (Wilquet et al., 2012). Considering the CO$ _{2}$ vertical profiles calculated from the SOIR measured spectra and the hydrostatic equilibrium, we could calculate the kinetic temperature profiles (Mahieux et al., 2015a). SOIR was sensitive to two isotopologues of water, $ ^{1}$H$ ^{16}$O$ ^{1}$H and $ ^{1}$H$ ^{16}$O$ ^{2}$H, which it could measure simultaneously and collocally. During many observations, SOIR also concurrently measured the CO$ _{2}$ density, such that the local temperature could be computed. Consequently, we were able to precisely compute the HDO/H$_{2}$O ratio in the Venus mesosphere at the terminator. Our individual ratios show a large variability as a function of time and space. We do not observe any systematic variation of the HDO/H$ _{2}$O ratio as a function of latitude or terminator side. Our mean values for the HDO/H$ _{2}$O ratio are in agreement with previous observations in the lower mesosphere (between 73 and 101 km, e.g. Donahue et al. (1982), Bjoraker et al. (1992), Bertaux et al. (2007), Fedorova et al. (2008), Krasnopolsky (2012)), and equal to 0.12, with a standard deviation of 0.08, constant with altitude. Above 100 km, we observe a steep increase of the HDO/H$ _{2}$O ratio, reaching a mean value of 1 at 120 km, with a standard deviation of 0.5. On top of presenting the SOIR retrieved values, we will compare the mean results with a 1D vertical model that includes molecular and eddy diffusions and chemical reactions to explain the SOIR/VEx retrieved HDO/$H$ _{2}$O vertical profiles. Bertaux, J. L., et al., 2007. Nature. Bjoraker, G., et al., 1992. Bull. Amer. Astron. Soc. Chamberlain, S., et al., 2020. Icarus. (submitted). Donahue, T., et al., 1982. Science. Fedorova, A., et al., 2008. J. Geophys. Res. Krasnopolsky, V., 2012. Icarus. Mahieux, A., et al., 2008. Applied Optics. Mahieux, A., et al., 2012. J. Geophys. Res. Mahieux, A., et al., 2015a. Planet. Space Sci. Mahieux, A., et al., 2015b. Planet. Space Sci. Mahieux, A., et al., 2015c. Planet. Space Sci. Nevejans, D., et al., 2006. Applied Optics. Vandaele , A. C., et al., 2016. Adv. Space Res. Vandaele, A. C., et al., 2015. Planet. Space Sci. Wilquet, V., et al., 2012. Icarus.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.773M