Monitoring of Martian water ice clouds over one Martian Year with TGO/ACS-MIR

The Atmospheric Chemistry Suite (ACS) MIR channel onboard the ESA-Roscosmos Trace Gas Orbiter (TGO) (Korablev et al., 2018, 2019) probes the Martian atmosphere in the 2.3 – 4.2 µm spectral range using the Solar Occultation technique. ACS-MIR has now provided infrared observations of the Martian atmosphere over more than one and a half regular Martian Year since the end of the 2018/MY34 Global Dust Storm (GDS).

We analyzed this ACS-MIR dataset to detect the presence of water ice particles in the Martian atmosphere and retrieve their size from the 3 μm atmospheric absorption signature. Each observation results in a vertical profile of ice particle size within the cloud layer, with a vertical resolution of a few kilometers. The temporal and spatial sampling provided by the 2-hour period of TGO’s orbit allows us to observe the seasonal and latitudinal trends of the water ice clouds, with variations of about 20 to 40 km of the cloud’s altitude.

The method was first applied solely to the 2018/MY34 GDS year (Stcherbinine et al., 2020). This first study notably revealed the presence of small-grained clouds at very high altitudes (above 100 km) at the onset of the MY34 GDS, along with the presence of large water ice particles (r_eff > 1.5 µm) up to 65 km during the storm.

Data acquired during MY35, where no GDS occurred, provides a reference to be compared with the observations obtained during the MY34 GDS. We observe that the maximum altitude of the water ice clouds increases by about 10 km during the GDS compared to a nominal year, which suggests that the GDS significantly impacts water ice cloud distribution.