JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

P (Space and Planetary Sciences ) » P-PS Planetary Sciences

[P-PS06] Science of Venus: Venus Express, Akatsuki, and beyond

convener:Takehiko Satoh(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Kevin McGouldrick(University of Colorado Boulder), Hideo Sagawa(Kyoto Sangyo University), Thomas Widemann(Observatoire De Paris)

[PPS06-09] Determination of the homopause altitude on Venus from SOIR/VEx observations

★Invited Papers

*Arnaud Mahieux1,2, Hiromu Nakagawa3, Nao Yoshida3, Ann Carine Vandaele1, Roger Yelle4, Séverine Robert1, Shohei Aoki1,5, Arianna Piccialli1, Loïc Trompet1, Yasumasa Kasaba3 (1.Royal Belgian Institute for Space Aeronomy, Brussels, Belgium, 2.The University of Texas at Austin, Austin, Texas, 3.Tohoku University, Sendai, Japan, 4.University of Arizona, Tucson, Arizona, 5.Université de Liège, Liège, Belgium)

Keywords:Venus, Mesosphere, Homopause

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 (~0.2 cm-1) and spectral sampling (~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): CO2 (Mahieux et al., 2012), CO (Vandaele et al., 2015), H2O (Chamberlain et al., 2020), HCl, HF (Mahieux et al., 2015c), SO2 (Mahieux et al., 2015b), and the aerosols (Wilquet et al., 2012). Considering the CO2 vertical profiles calculated from the SOIR measured spectra and the hydrostatic equilibrium, we could calculate the kinetic temperature profiles (Mahieux et al., 2015a).

The homopause is an altitude region separating the homosphere and the heterosphere. In the homosphere, eddy diffusion exceeds molecular diffusion, such that all the gases are all well mixed. Their vertical distribution all have the same scale height. In the heterosphere, the opposite occurs, and gases are not well mixed anymore. Consequently, each species follows its own scale height, function of the species’ molecular weight.

In this work, we present computations of the mean homopause altitude at the terminator based on the CO and CO2 simultaneously measured number density profiles, and the corresponding temperature profiles. We found out that it is located at a pressure level of 10-4 mbar (~120 km). The results are compared to a 1D vertical diffusion code, which accounts for eddy and molecular diffusions.

Chamberlain, S., et al., 2020. SOIR/VEx observations of H2O at the terminator in the Venus mesosphere. Icarus. (submitted).

Mahieux, A., et al., 2008. In-flight performance and calibration of SPICAV/SOIR on-board Venus Express. Applied Optics. 47, 2252-65.

Mahieux, A., et al., 2015a. Update of the Venus density and temperature profiles at high altitude measured by SOIR on board Venus Express. Planet. Space Sci. 113-114, 309-320.

Mahieux, A., et al., 2015b. Venus mesospheric sulfur dioxide measurement retrieved from SOIR on board Venus Express. Planet. Space Sci. 113-114, 193-204.

Mahieux, A., et al., 2012. Densities and temperatures in the Venus mesosphere and lower thermosphere retrieved from SOIR on board Venus Express: Carbon dioxide measurements at the Venus terminator. J. Geophys. Res. 117, E07001.

Mahieux, A., et al., 2015c. Hydrogen Halides measurements in the Venus upper atmosphere retrieved from SOIR on board Venus Express. Planet. Space Sci. 113-114, 264-274.

Nevejans, D., et al., 2006. Compact high-resolution space-borne echelle grating spectrometer with AOTF based on order sorting for the infrared domain from 2.2 to 4.3 micrometer. Applied Optics. 45, 5191-5206.

Vandaele , A. C., et al., 2016. Contribution from SOIR/VEX to the updated Venus International Reference Atmosphere (VIRA). Adv. Space Res. 57, 443-458.

Vandaele, A. C., et al., 2015. Carbon monoxide short term variability observed on Venus with SOIR/VEX. Planet. Space Sci. 113-114, 237-255.

Wilquet, V., et al., 2012. Optical extinction due to aerosols in the upper haze of Venus: Four years of SOIR/VEX observations from 2006 to 2010. Icarus. 217, 875-881.