High-altitude CO2 clouds on Mars: OMEGA and HRSC observations

Abstract : The Martian climate hosts a rare phenomenon of condensation of the bulk atmosphere. CO2 condenses on the polar ice caps, but also forms clouds in the atmosphere. The existence of low-level, convective CO2 clouds in the polar night was indirectly discovered by MOLA [1,2] and modeled in some studies [3-5]. Recently several satellite instruments [6-9] have observed CO2 clouds also near the equator, but at high altitudes where the temperatures are low enough for CO2 condensation. Montmessin et al. [7] identified spectroscopically from MEx/OMEGA observations these high-altitude clouds to be composed of CO2 ice crystals by modeling the CO2 ice spectral signature that was observed in a deep CO2 gas absorption band at around 4.3 μm. In this work we have used the OMEGA [10] and HRSC [11] observations to map the occurrences of the high-altitude CO2 clouds and their properties. We have also compared the observations to the predictions of the LMD Mars Global Climate Model (LMD-MGCM) [12] and in particular its improved version that extends to the upper atmosphere [13].
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Anni Määttänen, Franck Montmessin, B. Gondet, H. Hoffmann, F. Scholten, et al.. High-altitude CO2 clouds on Mars: OMEGA and HRSC observations. Third International Workshop on Mars Polar Energy Balance and the CO2 Cycle, Jul 2009, Seattle, WA, United States. pp.37-38. ⟨hal-00484879⟩

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