Figure 10. Water vapor vertical profiles and saturation ratio obtained by SPICAM IR occultations in MY29 (B) and ACS NIR observations in MY35 (C) and MY36 (D) at Ls=75°-100° in northern and southern hemispheres. Panel A presents the latitudinal coverage of occultations.

On the contrary, Poncin et al. (2022) did not find evidence for large or widespread supersaturation in the Martian atmosphere. From CRISM analysis they conclude that during the aphelion season the atmospheric water is close to saturation when clouds are present and can reach the supersaturation ratio of 2 to 3 at most at 10–50 km. During the dusty season subsaturation was prevalent, in agreement with previous CRISM study by Clancy et al. (2017). Also, comparison of NOMAD water profiles and MCS atmospheric temperatures during the GDS decay and the “C” storm of MY34 has shown one case of saturation ratio reaching 5 at the top of the cloud layer and below 2 in other cases. These results were more in line with traditional understanding that water vapor is close to saturation in presence of water ice clouds. However, the analyzed water-temperature combinations from CRISM-MCS or NOMAD-MCS datasets were not completely simultaneous. Also, results of Poncin et al. (2022) and ACS TGO do not exclude each other. As shown in Figure 10, the water vapor mixing ratio and its saturation state are very dynamic and change dramatically from occultation to occultation with latitude and Ls not only in the dusty season presented in Fedorova et al. (2020) but in the aphelion season as well. Solar occultation observations at terminator may reflect both the morning and evening conditions where a strong temperature contrast can stimulate fast processes. Connour et al. (2020) have reported twilight cloud bands routinely forming past the evening terminator (18:00–19:00 local time) during the MY 34 GDS as a result of rapidly changing temperatures. The cloud bands in the IUVS/MAVEN images were often latitudinally continuous, spanning over 6,000 km, and reaching 40–50 km altitudes. Such clouds were also detected in the ACS observations during GDS (Fedorova et al., 2020; Luginin et al., 2020), together with strong lifting of supersaturated water. The morning-to-evening difference of the saturation state observed by ACS (Fig. 9) supports that supersaturation cases can be related to semidiurnal thermal tides in the atmosphere.

The recent study of the MY34 GDS with Mars Assimilated Remote Soundings (OpenMars) dataset of Mars GCM group in the Open University (Holmes et al., 2021a) has shown that discrete layers of supersaturation above 60 km exist across all latitudes during the MY34 dusty season with diurnal variation in the saturation state of the atmosphere. This is consistent with ACS NIR observations not only for MY34 but also for MY35. General consistency of the assimilation and observations gives promising perspective of the water vapor saturation modeling.