Observations of CO2 clouds on Mars from TIRVIM and NIR solar occultation measurements onboard TGO

<p>Carbon dioxide is the major constituent of the Martian atmosphere. Its seasonal cycle plays an important role in atmospheric dynamics and climate. Formation of the polar CO₂ frost deposits results in up to 30% of atmospheric pressure variations as well as in dramatic change in surface reflectance and emissivity. Another case of carbon dioxide condensation is formation of a CO₂ clouds that are still poorly studied, despite the fact that they have been observed by a number of instruments [1&#8722;6] on the orbit of Mars.</p><p>In this work, we will present first results of CO₂ clouds observations from a combination of thermal-infrared (1.7&#8722;17 &#181;m) and near-infrared (0.7-1.6 &#181;m) spectra measured by TIRVIM and NIR instruments onboard the ExoMars Trace Gas Orbiter (TGO) in solar occultation geometry. These instruments are part of the Atmospheric Chemistry Suite (ACS), a set of three spectrometers (NIR, MIR, and TIRVIM) that is conducting scientific measurements on the orbit of Mars since the spring of 2018 [7].</p><p>This work was funded by Russian Science Foundation, grant number 20-42-09035.</p><p><strong>References</strong></p><p>[1] Montmessin et al. (2006). Subvisible CO2 ice clouds detected in the mesosphere of Mars. Icarus, 183, 403&#8211;410. https://doi.org/10.1016/j.icarus.2006.03.015</p><p>[2] Montmessin et al. (2007). Hyperspectral imaging of convective CO2 ice clouds in the equatorial mesosphere of Mars. Journal of Geophysical Research, 112, E11S90. https://doi.org/10.1029/2007JE002944</p><p>[3] M&#228;&#228;tt&#228;nen et al. (2010). Mapping the mesospheric CO2 clouds on Mars: MEx/OMEGA and MEx/HRSC observations and challenges for atmospheric models. Icarus, 209, 452&#8211;469. https://doi.org/10.1016/j.icarus.2010.05.017</p><p>[4] McConnochie et al. (2010). THEMIS-VIS observations of clouds in the Martian mesosphere: Altitudes, wind speeds, and decameter-scale morphology. Icarus, 210, 545&#8211;565. https://doi.org/10.1016/j.icarus.2010.07.021</p><p>[5] Vincendon et al. (2011). New near-IR observations of mesospheric CO2 and H2O clouds on Mars. Journal of Geophysical Research, 116, E00J02. https://doi.org/10.1029/2011JE003827</p><p>[6] Jiang et al., (2019). Detection of Mesospheric CO 2 Ice Clouds on Mars in Southern Summer. Geophysical Research Letters, 46(14), 7962&#8211;7971. https://doi.org/10.1029/2019GL082029</p><p>[7] Korablev et al., (2018). The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev. 214, 7. doi:10.1007/s11214-017-0437-6</p>