A study on CO2 supersaturation in the Martian southern polar night using Mars Global Surveyor radio occultation profiles rederived with Mars Climate Sounder temperature climatology

We investigate CO2 supersaturation in the Martian southern polar night using rederived vertical profiles from Mars Global Surveyor (MGS) radio occultation (RO) measurements. Supersaturation, which affects not only local condensation but also the polar and global atmospheric dynamics, occurs when temperatures fall below the CO2 saturation point. Conventional MGS-RO retrievals suffer from uncertainties in atmospheric composition, as they do not account for CO2 depletion due to its condensation onto the seasonal polar ice caps, and from the use of fixed or empirically chosen uppermost temperatures. To address these limitations, we apply a revised retrieval scheme that incorporates a latitude- and season-dependent estimate of the CO2 mixing ratio based on Mars Odyssey GRS argon data, along with a temperature climatology derived from Mars Climate Sounder (MCS) observations aboard the Mars Reconnaissance Orbiter. We find that the original RO data underestimated supersaturation occurrence by 10-20% inside, and overestimated it by a similar fraction outside, the polar night. The updated profiles reveal that CO2 supersaturation commonly occurs up to 15km altitude and ∼65◦S latitude, with seasonal and vertical variations peaking before the southern winter solstice. A comparison with MCS-derived surface ice temperatures shows general consistency, although notable vertical gradients and near-surface cold layers indicate complex boundary-layer thermodynamics. These results demonstrate that reducing key assumptions in RO retrievals yields improved constraints on Martian polar processes, providing new insights into the spatial and temporal behavior of CO2 supersaturation during southern winter.