Structure of the upper atmosphere of Venus as measured by the SOIR/VEx occultation experiment

The study of Venus' mesosphere and thermosphere plays a crucial role in understanding the planet's atmospheric processes, including the escape of water, as evidenced by the anomalously high [HDO/H₂O] ratio (Fedorova et al., 2008; Mahieux et al., 2024). Research on these atmospheric layers also helps improving photochemical models of Venus’ upper atmosphere.

The most extensive observational dataset was obtained by the SOIR spectrometer aboard Venus Express (Nevejans et al., 2006). SOIR recorded absorption lines in the infrared range (2.2–4.2 μm) using solar occultation, covering altitudes of 65–170 km. In addition to CO₂, the instrument detected minor constituents and isotopes such as H₂O, HDO, HCl, and SO.

This study presents vertical temperature and density profiles retrieved from CO₂ absorption spectra (2006–2014). The retrieval algorithm, developed at IKI, utilizes the temperature dependence of absorption line intensity under the hydrostatic equilibrium assumption. This method has been successfully applied to data from the ACS/ExoMars experiment on Mars (Fedorova et al., 2020; Belyaev et al., 2022). Unlike the alternative ASIMAT algorithm (Mahieux et al., 2010, 2023), which is limited to unsaturated absorption lines, the IKI method covers a broader altitude range.

The updated atmospheric structure will improve estimates of minor gas abundances, including verification of the anomalous [HDO/H₂O] ratio.

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