Martian CO profiles from the solar occultation experiment of NOMAD on board TGO

Carbon monoxide is one of the important minor species in the Martian atmosphere due to its role in the photochemical stability of the \ce{CO2} atmosphere and can also be used as a dynamical tracer. The SO spectrometer onboard the Trace Gas Orbiter (TGO) scans the Martian limb in the infrared provides transmittances with fine vertical sampling ($\sim 1$km). In the spectral region, the sounding of \ce{CO} is found to be reliable due to its strong and well separated absorption lines. Here, we present the retrieval scheme for \ce{CO} from the solar occultation observation. Our scheme obtains density profiles up to 100 km with a vertical resolution better than $5$km and errors below $15\%$. The observations for the last two seasons of Mars Year 34 (MY34, April 2018 - March 2019) are analyzed here. We found important results such as a strong depletion of CO density during the global dust storm (GDS) and a clear dynamical influence of global Hadley circulation on the CO distribution.