Presentation #113.03 in the session Martian Atmospheric Models, Local to Global.
The ExoMars Trace Gas Orbiter (TGO) was launched in 2016 and began science operations in April 2018. NOMAD (Nadir and Occultation for MArs Discovery) is one of four instruments onboard, made up of three spectrometers built to probe the atmosphere and surface of Mars in the infrared and ultraviolet wavelengths using solar occultation, limb and nadir viewing geometries (Vandaele et al., 2018). The main objective is to characterize the composition and structure of the Martian atmosphere, including the seasonal trends of atmospheric gases, dust and clouds.
The GEM-Mars Global Circulation Model (GCM) is a crucial part of the mission, supporting the observational planning, data retrieval and interpretation of results. GEM-Mars is a multiscale grid-point model, representing the atmosphere from the surface up to around 150 km (Neary and Daerden, 2018; Daerden et al., 2019). Scattering and absorption by both dust and water ice clouds are included. The dust distribution is computed with dust lifting by winds and dust devils and can be scaled to a climatology to represent specific conditions of a particular Mars year. Other physical parameterisations included in the model are gravity wave drag and low-level blocking, a 14-layer soil model with subsurface ice, CO2/pressure and water cycle as well as gas phase and photochemistry. The chemical species are transported and mixed by the resolved circulation, eddy diffusion and in the upper atmosphere, molecular diffusion. With the condensation/sublimation of CO2, the mixing ratios of the other non-condensable gases are adjusted.
GEM-Mars was recently applied for the analysis of the NOMAD observed distribution of water vapour, D/H and ozone during the 2018 global dust storm (Neary et al., 2020; Aoki et al., 2021; Daerden et al., 2022a,b). The seasonal cycle of carbon monoxide was also simulated and compared to NOMAD nadir observations (Smith et al., 2021).
We will present an overview of the model and recent improvements, as well as results from simulations performed for the interpretation of NOMAD observations.