Modelling the Martian Atmosphere with the GEM-Mars GCM in Support of the ExoMars TGO/NOMAD instrument

The ExoMars Trace Gas Orbiter has been observing the atmosphere of Mars for more than two Martian years, providing new insights into the phenomena driving its climate and composition. Simulations using a Global Climate Model (GCM) are a key part of this mission, supporting the observational planning, producing atmospheric fields to drive the data retrieval process and to help with the interpretation of the observations by filling in the spatial and temporal gaps in the data. This in turn helps with the evaluation of the model, leading to the improved numerical representation of the physical processes occurring in the atmosphere.

The GEM-Mars GCM 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.

We will present an overview of the GEM-Mars GCM in the context of the NOMAD mission, with some of the most recent results and the latest progress on model developments and improvements.